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Renewable Energy Boats Part I

By David Shaw

Updated 2014/02/17 to include GaA 
 Updated 2013/06/05 with a worked example in the Old Port
Updated 2013/05/08 to include reference to NASA
Updated 2013/05/05 to include reference to solar airplanes

Updated 2013/04/15 to include hybrid schematic
Updated 2013/10/11 to include Solana solar field 

***

Designing the M/Y Sharina: A Guide to Key Differentiating Factors in Designing Your Trawler describes the development of a specification to build a 55-ft trawler yacht. Includes a spreadsheet application to calculate electrical and HVAC requirements. 240 pg., ISBN-978-0-9694443-1-2.

EPUB format (eBook). DRM-free, meaning it's not tied to Kindle (I have it on my iPhone) and you can lend it to your friends.

USD $9.99 on Amazon. Stock #B0040V4B96

***

 Hybrids Are Cool

 There have been a lot of new developments on the renewable-energy front, so I thought I would take another look at renewable energy for boat propulsion. A few years ago I wrote that powering a trawler with solar energy would require towing a solar-barge larger than the boat. In the meantime, I ignored stories about solar boats because I figured they must all be hybrids of some kind. Hybrids are the cool way to go.

A diesel-electric hybrid with solar. In an emergency it is capable of using the house bank for propulsive power.

But still the headlines persisted about the miracle of renewable wind and solar energy:

• Holographic foil that is twice as efficient as typical photovoltaic (PV) solar cells, using light selection, deflection, and concentration. The Dresden-based company Apollon GmbH & Co claims this has 28% efficiency compared to a typical 17%.
• Modern silicon and indium-tin-oxide-based solar cells are approaching the theoretical limit of 33.7% efficiency but a research team at Princeton has used nanotechnology to create a mesh that increases efficiency over organic solar cells nearly threefold.
• Houses all over the world are being powered by roof-top solar panels, and selling excess energy back to the grid.
• PlanetSolar is the biggest solar ship in the world.
• Solar Impulse HB-S1A airplane left on a transcontinental flight acorss the USA on May 4.
• New solar cells adjust sensitivity for latitude.

So I thought maybe I was out of the loop too long and should have another look at this subject. I think there are only two possible renewals for powered boats:

• Solar
• Hydrogen

Wind is a non-starter because, well, if you want to use wind power, get a sailboat! Right?

Before I got back up to speed on solar, I did all kinds of calculations and scenarios before I got myself grounded again. Here's the short version (which has been getting longer).

According to NASA, the earth's surface receives a maximum of 137 Watts per square meter (W/m²) at noon at the equator when the sun is perpendicular. At other latittudes and sun angles the energy is less.

In practice, for an 8-hour summer day, 40 degree latitude, the sun delivers a total average of 600 W/m². Currently the best commercial solar panels are ~16% efficient. At an efficiency of ~16% on a perfect sun day this is a yield of 96 W/m² averaged over 8 hours (0.768 kWh).

Now, metric horsepower, widely used in the auto industry, is defined as 0.73549875 kilowatt (kW). Assuming we need 200 horsepower (hp) to drive a 70-ft boat, this is ~147kW. At 96 W/m² this equals 1,531 m² (16,472 ft²) of panel acreage [1 m² = 10.76 ft²]. And this is just for propulsion during daylight hours. There is no extra for storage in a battery.

The highest density commercial solar cell I can find has a capacity of 174 W/m² or ~16 W/ft². I don’t know the conditions, but let’s assume this marketing claim is realistic output even though it doesn't align with the preceding paragraph or the NASA figures. For our 147 kW motor we would need 845 m² (9,092 ft²) of panels. At most a 70-ft yacht would have less than 1,000 ft² of surface area, so you can see why most boats using solar have hybrid propulsion systems.

New developments promise to change this solar-scape but not enough.  The cost of silicon-based photovoltaics (PVs) has dropped enormously, making  them very cost-competitive. However, their efficiency of conversion remains very low and doesn't look to increase organically. One way of increasing efficiency is to use external and cumbersome focusing mirrors to concentrate sunlight.

Other technologies offer better promise. Gallium arsenide (GaA) PVs are around twice as efficient as silicon but their high expense has restricted them so far to applications in space. Several new fabrication techniques promise to make GaA cost-competitive with efficiencies as high as 40%. One approach uses a small plastic sphere on each cell to focus more light.

This still doesn't shift the calculus enough. Even at 100% efficiency at the equator noon we need 5.4 m² to drive one horse. Two hundred horsepower would require just over 1,000 m² .

 -- From Wikipedia

On land, Computerworld reports that Abengoa Solana has flipped the switch on a massive solar field near Phoenix AZ built with federal loan gurantees of $1.45 billion and a 30-year guaranteed contract for the output. The plant covers 3 square miles and generates 280 mW, or 3.347 W/ft^2.
Back on the water, the huge carbon-fibre catamaran PlanetSolar MS Tûranor has 537 m² (5,780 ft²) of 38,000 photovoltaic panels with an 18.8% yield. These are mounted on deck and on large fold-out wings [http://www.planetsolar.org/]. The panels feed six blocks of lithium-ion batteries, like those used in the Boeing Dreamliner. The reported maximum daily yield during one 24-hour period was 661 kWh. According to the logs, recharging each day typically took until noon. Build cost was of the order of USD $16 million.

And in the air, the Solar Impulse HB-S1A airplane can carry only the pilot. Using high-technology materials it weighs 3,527 lbs and has a gigantic wing span of 208 ft -- as much as an Airbus A340 or a Boeing 747. It has four 10-hp electric motors driving propellers. These are powered by 11,628 monocrystallane solar cells spread across every available surface. "With 200m² of photovoltaic cells and a 12 % total efficiency of the propulsion chain, the plane’s motors achieve an average power of 8 HP or 6kW," according to the design team. So if we had 100% efficiency the plane would have 67 hp average available. Build cost is reported to be 90 million Euros (USD $118 million).

People reading this stuff are seized by the vision and write things like, "This is awesome. Let’s get electric passenger airplanes as soon as possible." Or boats. Or cars.

Let’s cut to the chase with a real worked example. Assume a boat moored in Montreal’s Old Port at 45.5 degrees N and 73.35 degrees W. The sun’s azimuth angle varies between 20 and 68 degrees from winter to summer. Assume 365 perfectly sunny days and solar panels that are horizontal on the boat deck and do not track the sun’s azimuth and east-to-west travel. The average available energy over a year is 3.40 kW/m²/day. At 16% solar-panel conversion efficiency, this is only 0.56 kW/m²/day. This is why renewable energy needs government subsidies, and why it is a supplement on a boat.

Montreal - Incident Solar Energy on Horizontal Surface (kWh/m²/day)

Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sept	Oct	Nov	Dec
1.58	2.48	3.58	4.44	5.05	5.63	5.54	4.88	3.71	2.31	1.44	1.23
Average = 3.40

http://solarelectricityhandbook.com/solar-irradiance.html

The reality (do the math yourself) is that even with solar panels at 100% solar-conversion efficiency it isn't feasible -- for practical purposes -- to fully power a trawler only with a solar platform that is sized within the hull's boundary. It doesn't compute.

Next time we will look at hydrogen.

eBook Designing the M/Y Sharina Now Available

"Designing the M/Y Sharina: A Guide to Key Differentiating Factors in Designing Your Trawler" describes the development of a specification to build a 55-ft trawler yacht. Includes a spreadsheet application to calculate electrical and HVAC requirements. 240 pg., ISBN-978-0-9694443-1-2.

Has received good peer reviews, and early drafts of some chapters are found below. The Excel spreadsheet alone is worth the price.

EPUB format (eBook). DRM-free, meaning it's not tied to Kindle (I have it on my iPhone).

USD $9.99 on Amazon. Stock #B0040V4B96

Cheers!

HVAC Systems

HVAC Systems

The heating, ventilation and air-conditioning systems are a blend of loosely coupled systems to provide maximum energy efficiency and redundancy.

2009 © David Shaw
N.B. This article references an Excel spreadsheet available from the author.

Design Considerations

The basic heating, ventilation and air conditioning system is described below. Remember, the design goal is a year-round live-aboard in north-eastern North America. For completeness in understanding the trade-offs made, the engine cooling system, hot water and refrigeration and watermaker are also shown. Some of the design considerations are:

• One single fuel type on board
• Minimize AC loads
• Minimize sound transmission
• Pre-heat water for the water maker
• Maximize energy usage
• Maximize efficiency
• Minimize dependencies
• Provide redundancy

The requirement for a single fuel type effectively eliminated propane heating in favour of diesel. As discussed elsewhere, diesel is anyway much safer. It is also more efficient, providing around 140,000 BTU per gallon, compared to 91,000 for propane.

The Solution

Distribution

The first major issue was whether to use forced air or circulating water to distribute heating and cooling. In the beginning, memories of cold radiators in grade school in the dead of a Canadian winter, and the comfort of humidity control with forced air in modern homes predisposed me to forced air. Over time, I changed my mind several times. In the end, circulating water was chosen to:

• Reduce the size of ducts in the insulated space
• Eliminate a path for airborne noise and dirt from the engine room
• Reduce the general level of air-borne dust
• Eliminate the need for a cold-air return
• Minimise openings in watertight bulkheads
• Deliver a more even heat by reducing stratification
• Eliminate cold drafts on start-up

Like electric heating, hot-water heating is very dry. This is offset by ventilation, which introduces fresh air. A programmable thermostat is located in the forward passageway. In each living area, opening/closing individual radiators will control temperature manually.

Fig 10-1 – The Harworth Bubble stove is one of the few diesel fireplaces available– Photo with permission © Harworth Heating, http://www.bubble-stoves.co.uk/

In addition, to provide backup in the case of failure in a severe cold spell, a diesel bulkhead fireplace in the salon, such as the Kabola Old English Diesel Room Heater [4] or the Harworth Bubble [5] is also plumbed into the distribution system. Other types of bulkhead heater are available from Dickinson [6], Refleks [14] and Sigmar [15].Initially a fireplace was desired for lifestyle reasons, but as the design evolved it became a backup system. The Dickinson Bristol Diesel Cook Stove [6] in the galley can also heat the forward accommodation, but it is not part of the main distribution system. The main distribution system also routes through the towel rails in various compartments. These are switched out of the circulating water system in summer and heated with AC elements.

Ventilation

Fresh air ventilation is required to replenish oxygen removed by people and sources of combustion, and to dilute odours and pollutants. Local exhaust ventilation is required in heads and the galley to remove airborne odours before they spread through the boat. From a ventilation viewpoint, the most effective method is an integrated HVAC system with air distribution and local controls in each cabin. Such a system can include an air-to-air heat exchanger to precondition the temperature of the air and recover energy, and a humidifier/dehumidifier to control levels of indoor moisture. Humidity control is especially important in hot humid climates where unconditioned ventilation can deliver 1-lb of water per cubic foot of intake air.

Excess humidity causes condensation on windows and water pipes. It can blister paint, rust metal and warp wood, and cause electrical faults. Dust mites, fungus, mildew and mould thrive in humid conditions, aggravating allergies and sometimes damaging lungs. Insects like clothes moths, cockroaches and fleas also like high humidity.

People prefer a relative humidity of 30 to 50% and find anything much higher to be very uncomfortable.

Unfortunately I decided against an air distribution system in favour of a water system for heating and air cooling. This was to minimise the scope of pass-throughs in water-tight bulkheads but like many design decisions this had further consequences. It made an integrated ventilation/humidification system impossible.

The alternative to running fairly large air vents the length of the boat is local ventilation in the main zones of the boat. This is far from ideal. In both summer and winter the air intakes will be working against the air conditioning and heating systems, respectively, and deck-mounted dorades for intake and return air are multiple hull openings. The ventilation system must be designed carefully to minimise these risks of water entering.

Humidity control is also difficult with local ventilation; although it may be possible to incorporate small electronic dehumidifiers into the vents. Electronic dehumidifiers use small peltier heat pumps but consume a fair bit of electrical energy. For small vents, mechanical dehumidifiers don’t scale down, and desiccated dehumidifiers are overly complex.

If you plan to spend your time in hot humid climates, you should consider a solution that incorporates a dehumidifier.

Fig 10-2 – The combined HVAC system

Air Conditioning

A water-based chiller provides air conditioning. The chiller circulates chilled water through a water distribution system to the cabins, to cool them in summer. All pipes should be insulated to prevent condensation. (Similarly, if you opt for forced air, the ducts should be insulated.)

The heat exchanger can be water-air or water-water. A water-air exchanger would have to work against the heat in the engine room, so it makes more sense to use a water-water heat exchanger with a keel cooler as a heat sink. This is overall more efficient (the temperature differential is higher with water), and avoids generating extra heat in the engine room.

Additional cooling for one zone is provided by the Glacier Bay cold-plate refrigeration system [8]. (A high-efficiency 12-VDC old-plate design was chosen for the refrigeration to reduce AC loads, while not imposing a continuous DC load. Excess capacity may be used for air conditioning.)

Hot Water

Hot water is heated in several ways. In port in summer, the water is heated by standard electrical elements operating off the AC. In winter, it is heated by the water jacket on the diesel oven. If the oven is not in use, and there is no other source of heat, the hot water tank defaults to the electrical elements.

Under way, engine coolant circulates through the hot water tank, and hence to a water-water heat exchanger with keel cooler. Another feature of this design is that raw seawater is not circulated through the engine. There is a bypass circuit around the water heater that closes thermostatically when the heater is at temperature.

(The next article will describe a tankless design for a hot-water heater with a solar collector and engine pre-heat.)

In winter if the boat is out of the water, the engine may have to be run to charge the batteries. In this case, an optional water-air radiator in the engine room provides engine cooling.

Use an anti-scald, balanced-pressure shower valve (not a tempering valve!) on the showers to regulate the water to 120 F. This will avoid scalding people, and reduce water consumption. Bathers will be able to mix the water faster to a comfortable temperature.

Watermaker

For cold water expeditions, the water intake to the watermaker should be preheated.

HVAC Scenarios

With this integrated design, the following scenarios apply:

Fireplace in use:

• Central furnace is turned down

Oven in use:

• Central furnace is turned down
• Central hot water AC is turned off

Main engine in use:

• Central hot water AC is turned off

Central furnace fails:

• Fireplace and oven provide central and space heat

Central furnace and distribution system fail:

• Fireplace and oven provide space heat

Shore AC power fails:

• Oven provides hot water
• DC-AC inverter provides electrivity to hot water elements

Heating Requirements

Methods of calculating requirements for both heating and air conditioning tend to the arcane or the very simplistic. There are too many variables to consider, e.g., the colour of the deck paint affects the amount of heat gain inside. The author has developed a spreadsheet application that tries to strike a balance between simplicity and accuracy. When calculating heating requirements, it ignores heat gain through southern exposure windows in the daytime and heat loss through all windows at night. It also ignores sporadic heat gain from equipment and appliances.

The spreadsheet uses the following formula to determine heating requirements invBritish Thermal Units per hour (BTU/h) [1]:

BTU = V * T * K * B

where:

V = volume of the accommodation in cubic metres

T = temperature differential in degrees Celsius

K = dispersion coefficient (how heat ‘lossy’ is your boat)

B = 4 (conversion factor to BTU)

To calculate the Volume, for each living space multiply Length * Width * Height in feet as shown in the below table. Use judgement in deciding whether to list each space individually or as part of a section. The calculator will do the conversion to metric.

For T, if you need to convert degrees F to degrees C, the formula is:

C = (F – 32) * 5/9

The dispersion coefficient K is adapted from housing construction as follows:

K = 3.0 - 4.0 (Simple construction, simple windows - Not insulated)

K = 2.0 - 2.9 (Simple construction, simple windows - Poorly insulated)

K = 1.0 - 1.9 (Standard construction, double-pane windows - Moderately insulated)

K = 0.6 - 0.9 (Advanced construction, triple pane windows - Well insulated)

With K=3, the calculator yields 19 BTU/ft-sq while experts recommend 20 BTU/ft-sq, so we have good agreement at one end of the range. How aggressive you should get towards the other end is impossible to say. However, with the three heating systems specified for the boat there should be ample scope for increasing or decreasing the heat without upsetting the balance of the system. In a system that is under-sized, the furnace will run for long periods. In an over-sized system, the furnace will cycle frequently and run for very short periods. In general, a heating system should be sized 154% of the requirement, so it runs at about 65% duty cycle.

Accommodation Space Calculation
Area	L (ft)	W (ft)	H (ft)	V (cu ft)
Forward
Aft
Pilothouse
Salon

Ventilation Requirements

Ventilation rates can be expressed in several ways:

• Cubic feet per minute (CFM) or litres per second (L/s) of outside air brought into the boat
• CFM per person: CFM/p
• CFM per unit floor area: CFM/ft²
• Air changes per hour (ACH)

Standards for ventilation differ, and have varied over time subject to lobbying, energy efficiency doctrines and the emergence of sick building syndrome. A reasonable yardstick is somewhere in the range of 0.5-1.25 ACH or, more precisely, 1.0 ACH translating to around 1.66 CFM per 100 cubic feet of cabin volume. You can double check this to ensure at least 15 CFM/p.

For example, assume a boat having 6,000 cubic feet of volume and berths for five people. Using 1.0 ACH this yields 99.6 CFM and 15 CFM/p yields 75 CFM.

Maximum air velocity in ventilation ducts and vents should not exceed 2.6-3.3 ft/s (0.8-1.0 m/s) to minimise noise and differentials in air pressure. Air ducts for combustion systems can run as high as 40-66 ft/s (12-20 m/s).

Let’s work a complete example. Assume a salon of 1280 cubic feet. At 1.0 ACH this requires 21.3 CFM:

CFM = Volume * ACH/60 minutes

The corresponding vent area with a velocity of 2 ft/s is:

Vent Area = CFM/(Velocity * 60 seconds)
= 21.3/120
= 0.18 sq ft
= 25.6 sq in

Close enough.

In this case, we could put a 5- x 5-in intake vent at one end of the salon and a vent of the same size at the other end with an exhaust fan driving 2 ft/s.

Air Conditioning Requirements

Calculating air conditioning is more complex and so the answers are more varied. The next table gives three sets of estimates to illustrate the issue.

• Column A gives a series of BTU values derived from the buyenergyefficient.org web site [2].
• Column B is based on an expert rule of thumb of 14 BTU per cubic foot, plus an extra 1000 BTU for good measure.
• Column C uses the spreadsheet calculator.

Except for the last two data points, methods A and C are in good agreement, but I leave you to your own judgement.

This spreadsheet calculator is adapted from Air Conditioning Your Home [3], published by the Energy Office of Natural Resources Canada (NRCAN) and available from its web site. It appears to fall within the general range of the other methods, based on area alone. Most rules of thumb are designed for single rooms, or two rooms joined. The author's calculator considers numerous more factors:

• Number of occupants
• Area of each accommodation
• Area of windows and degree of sun exposure
• Energy efficiency of windows
• Shading of windows
• Degree of insulation in the boat
• Heat gain through the engine room bulkhead
• Heat gain from AC machinery in the accommodation
• Heat gain from DC machinery in the accommodationHeat gain from DC lights in the accommodation

Several approximations were made in adapting the NRCAN model. For example, houses have a fixed position, allowing us to calibrate the different heat gain from windows facing any compass quadrant. Boats are mobile, allowing windows to face any direction at any time. The calculator assumes the worse case, with one full side of the boat having maximum southern sun exposure, the other minimum, i.e., it is moored east-to-west.

The degree of insulation is set with the K factor in the heating calculation. The factor for heat gain through engine room bulkheads is a pure guess. The heat gain from AC and DC equipment is factored at 3.4 - 4.3, while NRCAN suggests 3.0 for AC appliances in a house.

Recommended Cooling Capacity (BTU/h)
Area (ft2)	Method (ft)
	A	B 14 BTU/ft2	C Calculator (K=0.7)
100 - 150	5,000	3,100	3,465
150 - 250	6,000	4,500	5,775
250 - 300	7,000	5,200	6,930
300 - 350	8,000	5,900	8,085
350 - 400	9,000	6,600	9,200
400 - 450	10,000	7,300	10,395
450 - 550	12,000	8,700	12,705
550 - 700	14,000	10,800	16,170
700 - 1,000	18,000	15,000	23,100
A. Based on http://www.energyefficient.org/ [2] B. Expert rule of thumb C. Sharina's Excel spreadsheet [3]

Zones

For heating, ventilation and air-conditioning distribution and control purposes, Sharina is divided into the zones in the next table. With a K=1, Sharina requires approx. 37,810 BTU/h of heating. The main diesel furnace supplies this, sufficient for the coldest weather.

HVAC Zones
Description	Zone	Distribution	Air Conditioning BTU (K=1)	Heating BTU(K=1)
Forward cabin	1	44%	24,349	16,637
Aft cabin	2	17%	9,408	6,428
Pilothouse	3	18%	9.961	6,806
Salon	4	21%	11,621	7,940
Engine room	5	-	-	?

But what happens in an emergency? In the event the furnace fails, the Bristol Pacific model diesel stove in the galley can provide 6,500-16,250 BTU to heat the forward accommodation. At the lower heat setting it could maintain a temperature differential of 21 C, while the higher one maintains Sharina’s design differential requirement of 55 C in the forward compartment.

At the lower setting, water pipes, etc., are protected down to -20 C, a not infrequent winter temperature, which is why the design requirement is the higher 55 C differential. Because the galley stove alone cannot heat the whole boat in the event of a furnace failure, additional heat has to be supplied by the diesel fireplace in the salon. A fireplace such as the Bubble produces only 3.5 kW (11,946 BTU), good for a 17 C differential overall. So it will only heat the pilothouse and salon, not the aft cabin.

Therefore in an emergency in the coldest weather we have a heating shortfall of 21,560 BTU (6 kW). This is not critical above deck in the salon and pilothouse, since there are no water pipes there. But it is critical in the aft head.

Finally, some heating has to be provided to the engine room to keep water tanks and pipes from freezing. Obviously some further development is required in the design of the back-up heating. Increasing the output of the diesel stove is not a good option, as this would tend to make it less useful as a cook stove. Perhaps the Bubble should be re-located to the aft cabin, but this negates its lifestyle purpose. More practical solutions are to shut off the water to the aft head and run the engine to keep the engine room warm. Another solution is to have an aft engineroom and a contiguous forward accommodation space.

Summary

The HVAC system uses a blend of loosely coupled systems to provide maximum energy efficiency and redundancy for a year-round live-aboard. Fresh-air ventilation uses small zone-based air vents but this makes humidity control difficult. The heating and cooling systems use a shared circulating-water distribution system to minimise bulkhead pass-throughs. Heating is by a diesel furnace with backup from a diesel fireplace. Cooling is by a chiller with keel cooler, with backup from the cold-plate refrigeration system. Hot water is heated by the engine, the diesel oven, a solar collector or AC elements using shore power or the house bank. The provided calculator gives heating and air conditioning requirements in BTU/h.

References

1. TenPoint Ltd, http://www.tenpoint.co.uk/BTU_formula.htm

2. Consumer Federation of America, http://www.buyenergyefficient.org/buy.html

3. Adapted from Air Conditioning Your Home, Natural Resources Canada, http://oee.nrcan.gc.ca/english/

4. Old English Diesel Room Heater, Kabola, http://www.kuranda.co.uk/kabola_heat.html

5. Bubble Stove, http://www.bubble-stoves.co.uk/databb

6. Bristol Diesel Cook Stove, Dickinson, http://www.dickinsonmarine.com/

7. Zarsky Water Chillers, http://www.waterchillers.com/

8. Arctic Air, Air Conditioning, Glacier Bay, http://www.glacierbay.com/

9. Hurricane Heating Systems, International Thermal Research Ltd., http://www.hurricaneheater.ca/home.htm

10. Webasto, http://www.webasto-us.com/am/en/am_marine_heaters.html

11. Kabola Heating Systems, http://www.kabola.nl/

12. Wallas and Ardic http://www/scanmarineusa.com/

13. Espar, http://www.espar.com/

14. Refleks, http://www.hamiltonmarine.com/

15. Sigmar, http://sigmarine.com/

Data Network

It is relatively easy to build an inexpensive high-speed broadband network in your boat for Internet and streaming media like audio and video.
2008 © David Shaw

Design Considerations

The goal in this section is to design a data network with Internet connectivity, for the boat’s activities, business meetings and home entertainment.

A basic system consists of a satellite-based Internet Service Provider (ISP), an antenna connected to a receiver and modem, a router connected to the modem, a network connected to the router, and various devices connected to the network. These devices can be computers, printers or for home-entertainment. Any file servers or other critical devices should be on a Universal Power Supply (UPS).

Internet Service Provider

As we will see, it is relatively easy to build an inexpensive high-speed broadband network in your home, small office or on your boat. The components are widely available, costing in the hundreds of dollars each, not the thousands.

On land, the bottleneck is always the so-called last mile. The wiring or cabling between your Internet Service Provider (ISP) and your location determines whether you can use low-speed 28k or 56k dial-up, or a high-speed service like DSL.

For a boat, the bottleneck is the satellite service, and its geographic coverage, as provided by a global ISP. Typically with satellite service, the download speed (e.g., 2 Mb/s) is faster than the upload speed (e.g., 512kb/s). The Internet connectivity is sometimes bundled with telephone and fax service. Telephone service, called Voice Over IP (VoIP) is also feasible over the Internet. In North America, major telephone companies were readying VoIP service in late 2004.

Global satellite ISPs include: KVH [23], VSAT [24]. Satellite Signals has a web site listing regional providers around the world [25].

Router

A router is a kind of computer device that routes packets of data from one device to another. Think of it as a kind of switch. Routers also serve as gateways to the Internet. Routers suited for a small office or boat usually include four ports for direct cable connections and a firewall.

A firewall prevents intruders on your network as follows: Internet services are assigned a standard TCP/IP port number. For example, web browsing uses the http service at port #80, which you have seen in your browser as http:// in front of a www address. A firewall restricts access to the ports. If you close all ports except #80, outsiders cannot get direct access to your network while you can still surf the web. The UPnP protocol is insecure, so make sure you can turn it off. Typical vendors suited to a small office or boat are: Belkin, D-Link, LinkSys and NexLand [2-5]. If you have both a local and a satellite ISP, you may want to consider a balancing router like the NexLand, which will make switching more seamless. Routers are also available with a wireless function.

Switch

If you need more ports for direct connections than provided by your router, you can daisy chain a five-port Ethernet switch [3-5]. Typically, the router has a designated port for this.

Network Connectivity

Wireless is the Way to Go

Because we’re fitting out a new trawler, we can install a high-performance network for streaming media like video and audio. For every day use, phone-line, power-line and 802.11b wireless suffice. But for streaming media, in rank of performance, the choices in connecting a network are:

• Cable
• Gigabit Ethernet
• Fast Ethernet
• Wireless 802.11g
• Wireless 802.11b

Gigabit Ethernet and Fast Ethernet both require Category 5e cable, terminated in RJ-45 jacks.

Using Ethernet over cable gives the highest performance (bandwidth and speed). Think of speed as the length of time it takes you to go to the fridge for a beer. Think of bandwidth as the number of beers you bring back at one time. Think of performance as how fast you get drunk…. [9]

However, wireless (Wi-Fi) has the great advantage that you can work anywhere in the wireless reception area without being hooked up to or trailing a cable. Although 802.11b is too slow for streaming media, newer protocols like 802.11g are satisfactory. The other big advantage is that more and more devices, such as TVs and stereos, are available every day with wireless connectivity. Wireless is the future.

Wi-Fi has a range of 300 ft. Of course, wireless signals are degraded when they have to pass through walls, and will be reflected by steel bulkheads and hulls. These are not issues in a fibreglass hull.

The problem in a custom steel hull is that we don’t really know how the wireless will perform after everything is built. We can only assume that coverage will not be uniform. For example, a single wireless router in the pilothouse is unlikely to propagate through a steel hull via a companionway to the forward accommodation. But it’s remotely possible because the wavelengths are very short. To box clever, run Cat5e or Cat6 plenum cable from the incoming router to the salon and pilothouse, and also the fore and aft accommodation. At every termination point, you will need an AC power outlet, unless you use Power over Ethernet (PoE).

PoE uses an Injector located near the router to put a DC voltage on the Cat5 cable. Your wireless access points may be able to use this directly, through the RJ45 jack (looks like a telephone jack on steroids). These devices are sold as PoE-Compatible or Active Ethernet Compatible.

Devices that are not compatible can use a small converter called a Picker, Tap or Active Ethernet Splitter to connect to the regular DC power jack.

These termination points can be used for individual network connections or wireless access points. In the worst case, if the wireless router does not have enough coverage through the hull, you can install a wireless access point anywhere there is a termination for a data cable. This should ensure adequate coverage. Each access point should be set to a different channel, thereby setting up zones to cover different parts of the boat. In a steel hull, position access points so they have a good line-sight through doorways.

In addition, we may want to put a wireless antenna on the mast, to give coverage outside on the boat deck and in the aft cockpit.

To retrofit an older boat, pull plenum data cable through to distribution points wherever you can, and put Active Ethernet wireless routers at these nodes. If you can’t get cable through, or the wireless coverage is insufficient, consider using phone- or power-line adaptors with the resulting lower bandwidth.

Security

Because wireless networks broadcast their presence with a radio signal, other people can access them if you don’t secure them properly. Buy only access-point devices that have Wi-Fi Protected Access (WPA, WPA2) with MAC, and are capable of closing the network. Don’t buy devices with the older WEP security standard.

MAC (Medium Access Control) allows you to create an access control list (ACL). To do this, you enter the MAC address of all wireless devices allowed to access your network. If other devices attempt to log on, they are call-blocked.

Most wireless networks ship with a default password provided by the manufacturer, and automatically broadcast a default network name, called a Service Set Identifier (SSID). This means that an outsider can detect your network by looking for the radio signal and its default SSID, log-on using the SSID and default password, and gain access.

Fortunately WPA makes it easy to secure your network if you follow these steps [1]:

• Enable WPA, following the manufacturer’s instructions.
• Change the default password.
• Change the default network name (SSID).
• Close the network by blocking automatic broadcasting of the SSID. (You will still be broadcasting a wireless signal, but it will have no network name.)
• Enter the MAC address of all devices into the access-control list.
  

Finally, review the port settings in the firewall included with your router. Note that none of these measures will protect you against penetration by a skilled opponent. But unless you have state secrets aboard no one is going to go to the effort.

Devices

With a network in place, consider attaching some of these devices.

File Server

A file server is a computer where you store your files. Usually it will have a tape unit, or writeable DVD for backups. The file server is connected directly to the router with a network cable, so the two should be co-located. Whether you chose Linux or Windows for the server depends on your level of comfort. In my office, we run both. We regularly re-start (reboot) the Windows servers every month or so. Some of the Linux servers have been running for two years without a reboot. Network Area Servers (NAS) are available as network appliances. Usually these are Linux based but because they are designed as appliances they hide the operating system from you. You don’t have to be familiar with Linux to use them.

Print Server

An inexpensive wireless print server allows you to connect a printer to the network without using a print server (a dedicated computer) or connecting the printer to the file server. Wireless print servers are available from: Belkin [2], D-Link [3], Hewlett-Packard [7], LinkSys [4] and Netgear [8]. Hewlett-Packard makes printers such as the DeskJet 5850 with a built-in wireless server.

Fax Server

An inexpensive fax server will let you send and receive faxes from any Windows program or attached scanner [32].

Voice Over IP

Voice over IP (VOIP) is a mechanism for routing telephone calls over the Internet instead of through the switching circuits and trunk cables of the telephone companies. It’s a new technology that has matured very rapidly. Its chief advantage is very low-cost flat rates for long-distance calls. Its chief disadvantage is possible delays in the signal. VOIP went commercial in 2004. VOIP also operates over Wi-Fi, where it is called VoWIP. VoWIP should be available from HP, Mitel, Motorola, NEC, Nokia and others in mid-2005. To work with VoWIP, your wireless access points must have SpectraLink Voice Priority (SVP).

Cameras

Wireless cameras are an excellent way to provide security or monitor blind spots. Some places to consider are:

• Boat deck
• Aft cockpit
• Side decks

Numerous cameras are available for indoor use. For outdoor use, consider the Toshiba IK-WB11A Wireless Network Camera [6]. With its half-inch CCD sensor, it delivers outstanding image quality. Its rated operating range for temperature (-4° to +122° F) and humidity (up to 90 %) make it suitable for all but the most extreme environments.

The IK-WB11A supports resolutions ranging from 160-by-120 to 1,280-by-960 pixels. It delivers 112 degrees of pan and 54 degrees of tilt, plus a 5X digital zoom control. It's based on 802.11b technology, which is compatible with an 802.11g network. Unfortunately it only supports WEP not the more secure WPA. This is an acceptable risk in a boat.

Entertainment

Personal Video Recorder

A Personal Video Recorder (PVR), also called a Digital Video Recorder (DVR) performs the same function as a VHS tape recorder, but instead stores the program in a compressed digital format (MPEG) on a hard drive like that in your computer. Unlike VCRs, DVRs let you easily skip around, wind back, pause, jump ahead, and skip commercials. (A proposed USA federal law makes it illegal to skip commercials!) Some of them are combined with recordable DVDs. Others are combined with satellite and cable receivers, and work only with a subscription service. Stand-alone units record off-the-air.

Products are available from: EchoStar, Fusion, Hughes DirecTV, LG Electronics, MythTV, Pace, Panasonic [13], Pioneer, ReplayTV [28], Sky [29], Thompson, TiVo [14], Toshiba, Zenith.

The Electronic Frontier Foundation publishes a cookbook for building your own before the USA FCC restrictions of July 30, 2005 are imposed on manufacturers [26]. ExtremeTech also has DIY guide [27].

Music Receiver

Products are available from: Apple [20], Creative Labs [12], LinkSys [4], Slim Devices [22], NetGear [8] and others.

Media Receiver

A media receiver (also known as a media hub or media adapter) lets you stream digital audio, photos, and video files from the file server or a networked computer to a stereo system or TV set. Typically a media receiver plays MP3, WMA, PLS, RMP, and M3U audio formats; displays pictures in JPG, GIF, BMP, and PNG graphic formats; and plays composite Video, S-Video, and RCA audio on the TV. Products are available from: ADS [19], Creative Labs [12], D-Link [3], Hauppauge [16], Hewlett-Packard [15], LinkSys [4], Omnifi [18], Philips [20], Prismiq [10], SMC Networks [11], Sony [17] and others.

DVD Player

Most DVD players have an embedded code that matches the code, called a region lock, in DVDs that you buy locally. This means that a DVD player sold in the USA won’t play DVDs bought in Europe or any of the other four regions (six total). This allows the media companies to charge different local rates for the same content. The movie you buy in the USA for $12 might be legitimately available in Mexico for $2. It also means, for a passage maker, that you can’t buy locally on your next world voyage. Fortunately, some code-free DVD players are available from outlets like CodeFreeDVD [30].

Digital Music System

A digital music system consists of a hub attached to a PVR or other network area storage (NAS) device. The hub drives multiple remote speakers. Systems such as the SONOS™ use wireless distribution up to 32 zones and can play different tunes in different zones [31].

Summary

Internet connectivity supports the boat’s activities, business meetings and home entertainment. Basic system is a satellite-based Internet Service Provider, antenna, receiver and modem, router and network. Network is gigabit Ethernet over Cat5e cable and 802.11g wireless nodes. Security is provided with a firewall, WPA and MAC. Connected devices include computers; file, printer and fax servers; VOIP, cameras, personal video recorders, music and media receivers.

References

1. Wi-Fi Alliance, http://www.wi-fi.org/

2. Belkin, http://www.belkin.com/

3. D-Link, http://www.dlink.com/

4. LinkSys Group, Inc., http://www.linksys.com

5. NexLand Inc, http://www.nexland.com/

6. Toshiba, http://www.toshiba.com/taisisd/netcam/products/wb11a.htm

7. Hewlett-Packard Co., http://www.hp.com/

8. Netgear, http://www.netgear.com/

9. Attribution unknown.

10. Prismiq Inc., http://www.prismiq.com/

11. SMC Networks Inc., http://www.smc.com/

12. Creative Labs Inc., http://www.creative.com/

13. Matsushita Electric Corp. of America, http://www.panasonic.com/

14. TiVo Inc., http://www.tivo.com/

15. Hewlett-Packard, http://products.hp-at-home.com/

16. Hauppauge, http://www.hauppauge.com/

17. Sony, http://www.sonystyle.com/

18. Omnifi, http://www.omnifimedia.com/

19. ADS Tech, http://www.adstech.com

20. Royal Philips Electronics, http://www.philips.com/

21. Apple Computers, http://www.apple.com/

22. Slim Devices, http://www.slimdevices.com/

23. KVH Industries, Inc., http://www.kvh.com/

24. VSAT Systems, http://www.vsat-systems.com/

25. Satellite Signals, http://www.satsig.net/

26. Electronic Frontier Foundation, http://www.eff.org/broadcastflag/hdtv-introHY.php

27. ExtremeTech, http://www.extremetech.com/article2/0,3973,1121844,00.asp

28. ReplayTV DNNA, ?

29. Sky, http://www.sky.com/

30. CodeFreeDVD, http://www.codefreedvd.com/

31. SONOS™, http://www.sonos.com/

32. SnappySoftware.com, http://www.snappysoftware.com/

DC/AC Systems

An efficient electrical system can be designed to run for a day off a house bank. A separate AC generator is not required.
© 2008 David Shaw

Design Considerations

In the previous chapter, we established that “the design objective of Sharina’s electrical system is to run as much as possible on the DC system and use an inverter for AC while, hopefully, eliminating the need for a separate AC generator.” In addition, it should run on shore power anywhere in the world.

We then outlined a scenario that maximised the use of DC, and used AC only where it made most sense. This minimises the size and cost of the inverter.

The assumption in not having a genset is that the boat will be underway at least one hour every day, or shore power will be available, or you can simply run the engine for an hour if you are moored.

If you plan to be moored extensively in other circumstances, then you should consider a genset. It doesn’t make sense to run a 200-300 horsepower (hp) engine for long periods to provide charging when a 20-hp engine will suffice. But remember that you should run the main engines to operating temperature at least once a day to eliminate condensation in the cylinders, anyway, so we might as well use this period to charge the batteries.

In designing the system, the DC and AC systems should be loosely, not tightly coupled, with no single point of failure, as discussed in Chapter Two. Both AC and DC systems should have surge protection. A trickle-charge system will provide some degree of backup to the alternator and charger.

The worst-case scenarios we want to cover for Sharina’s intended usage are:

• The AC system fails, but the boat’s critical systems continue running on DC.
• Both the AC and main DC systems fail, but there is a backup DC system for super-critical instruments and navigation systems.
• The main charging system and/or shore power fail while the boat is unattended, but there is a backup trickle-charge system.

The shore-power requirement is complicated by the various standards around the world. But first, some background.

Because the voltage at your house will be lower than at the power station, 120 VAC is sometimes referred to as 110, 115 and sometimes 117 V. Similarly, 240 VAC is often called 220 V.

AC does not have the same energy as direct current because it reverses polarity, swinging from positive to zero to negative to zero and back to positive. To equate the two, most AC voltages are given as the root-mean-square (RMS) voltage, which simply means the equivalent-to-DC voltage (Vrms = 0.7 * Vpeak). This makes power calculations easier, i.e., a Watt is a Watt is a Watt.

In North America, AC systems are 60-Hz and either 120 or 240 Vrms. Because the 240 VAC circuit consists of two 120-VAC circuits stacked together, the AC is double-phase. Service is usually available in 30, 50, 100 or 200 amps. While homes used to function adequately on 50 A, most modern homes have 200-A service. In Europe and elsewhere, service is usually 50-Hz 230 VAC single phase, i.e., a single circuit.

For simplicity, in most of this chapter we will refer to AC only without specifying the voltage. DC systems are usually 12, 24 or 48 V. Again, for simplicity, we will refer just to DC.

In general, DC is somewhat safer than AC in that an accidental shock is less likely to fibrillate the heart. All the same, note that in either case:

• 1 mA causes a tingle
• 5 mA causes a slight shock
• 50 to 150 mA can result in death through muscle breakdown and renal failure
• 1 to 4 A can cause death through fibrillation of the heart
• 10 A causes cardiac arrest

As a good practice, treat both AC and DC with the same trepidation.

The DC Primary System

12 or 24

The boat's primary electrical system is DC. In the size of boat we are discussing, 48 VDC is uncommon, so we will be choosing between 12 or 24 VDC. Generally, 24 VDC is preferable but, as noted in the previous chapter, some equipment may be available only in 12 VDC.

24-VDC is better because for a given amount of energy consumption in Watts, it requires fewer amps running through the wires than a 12-VDC system. The lower the voltage the higher the current (amps = Watts/Volts). For example, a 100-W device draws approximately 8.3 A at 12 V and 4.2 A at 24 V.

Higher current has disadvantages. The higher the current draw, the thicker the wiring is required (and the bigger the spark when you accidentally ground it). Thick wiring is more expensive and hard to install and maintain – think jumper cables for boosting your car.

Higher voltages are also feasible. Large ships have long used a higher voltage DC bus. Glacier Bay [25] is pioneering the adaptation of this technology to smaller yachts. Its OSS system runs at around 150 VDC. Some of the advantages this yields are smaller wiring, more efficient thrusters and windlasses, and compatibility with most shore power around the world and existing resistive devices like stoves.

Wires also have resistance and, when a current passes through them, this causes a voltage drop along the length of the wire. The higher the current, the higher is the drop in voltage. This voltage drop limits the practical length of a wire. The maximum run for 12-VDC wiring is around 30-35 ft, which translates into a boat length of around 50 ft, given a midships battery, and the need to run wires around corners.

Also, for various reasons the efficiency of DC-AC inverter circuits is better the higher the DC input voltage. Therefore, a 24- or even 48-VDC system is better than a 12-V one. As mentioned, the downside to 24 V is the wider range of equipment available for 12 V.

To accommodate both 12- and 24-VDC equipment, it is possible to design a battery system for 12/24, in somewhat the same way that North American houses have 110/220 VAC. This system would use high-amperage blocking diodes to split the two voltage circuits.

A better approach, if you select a 24-VDC system and some equipment is available only in 12 VDC, is to use individual 24-12 VDC, solid-state, low-noise controllers with voltage regulation. These start as low as $16 for a unit suited to power a radio. Obviously you should keep some spares on board. Using the individual controllers eliminates the need for an extra wiring system, complexity in the house bank, and dependence on a single set of high-performance diodes.

At this stage, in the first iteration, Sharina was going to have a 12-VDC electrical system. This design hit the wall when I worked out the specification for the watermaker. The key differentiating factor here is the number of people on board. More people need more water and, above a certain size, watermakers are 24 VDC.

The trend in the market is to 24 VDC, so that should be your first choice, anyway. However, if your boat is less than 50 ft, 12 VDC is probably still your best price-performance option.

Second only to discussions about one house bank or two, are discussions about bonding or not bonding the electrical circuits. The simple fact is that all electrical circuits have to have a common ‘ground’. On shore, this is often the earth. Bonding means connecting all the ground points together with an extra run of wires.

In all cases, the DC system must be a "floating ground" (DC negative bus) type of system, with an insulated return, fully isolated from the hull and all the hull fittings. This means that no electrical items (including common appliances) have a local ground to the hull (remember the double pin lamps in the previous chapter?). Instead, all ground returns are tied to a Common Grounding Point (CCG).

For example, all engine fittings are double insulated. The engine is electrically isolated from the hull via flexible mounts and flexible coupling. A grounding wire runs from the alternators to the DC negative bus. This might seem confusing, because the CCG itself is grounded to the hull. However, a CCG avoids stray electrical currents running through the hull and causing electrolysis. It also provides a grounding point for the lightening-protection system.

Having selected the voltage, the next phase in the design of the electrical system is to determine the requirements for the DC battery primary system – the house bank. The main considerations are:

• Load
• Battery type
• Layout
• Capacity
• Alternator
• Trickle charge

Load

Load is measured in total daily amp-hours (AH), which is simply the average current drawn per hour times 24 hours. Calculating this is a major task subject to much second-guessing. The first step in calculating load is to determine the combined DC and AC AH load for all ‘appliances’. Use a spreadsheet to list each item and its wattage or current draw, depending on which is available. For the DC, make sure you work entirely in either 12 or 24 V.

For each item, estimate the duty cycle (how long it will be used each day). Do a separate tally for fixed loads (e.g., instruments) and intermittent loads (e.g., coffee maker). If in doubt it is safer to over-estimate the duty cycle. But don’t go overboard. If you overestimate too much you might have to go back and tweak the numbers more realistically when you realize that you need to tow a substation behind you on a barge to supply your electrical requirements. All estimating processes must be subject to a reality check. It’s better to get each number as exact as possible, then add a fudge factor to the total, rather than fudge numbers individually.

In addition, you need to calculate the peak and surge requirements. To estimate the peak demand, determine which of the largest appliances will be used simultaneously. To estimate the surge demand, determine the surge on start up of large AC motors. (DC motors do not have a surge.)

Use whichever number is the highest for all future calculations. Let’s call this the Total Daily Load.

Battery Types

Battery types can be classified half a dozen different ways, so we will cut to the chase. On board a trawler, we need rechargeable lead-acid batteries for three different applications:

• Starting the engines
• Emergency lighting in the passageways
• Powering the equipment

These applications require different types of battery.

Starting the engines requires a vehicular-type battery that can provide a very short burst of very high current to crank the engine and provide ignition. This is sometimes called an SLI battery (starting, lighting, ignition). SLI batteries are slow to recharge. Other vehicular types are traction (also called RV and marine) and stationary (also called standby and float). Traction batteries are used in golf carts and (I guess) RVs.

For emergency lighting and backup power supplies, standby batteries, e.g., lead-calcium, are used. Typically they will provide juice to a lamp for 1.5 hours.

For the house bank, although traction batteries are sometimes used, what we really need is a true deep-discharge (DD) battery. Unlike an SLI, a DD provides high levels of current for a long period, and re-charges very quickly. Traction batteries have a slightly lower cost, but overall efficiency and performance will be better with DD batteries.

All of the above types are available in flooded or sealed sub-types. Flooded batteries are an older design. Internally they emit oxygen from the positive electrode and hydrogen from the negative one. This has to be vented to the outside to release pressure, i.e., they lose water and you have to top them up regularly. They have a relatively high internal resistance, which causes them to lose their charge by as much as 1% per day. During charging, they can lose 15-20% in heat losses.

Sealed batteries are just that, and they require no topping up. They use gel or absorption glass mat (AGM) to immobilize the acid solution. Unlike flooded batteries, they are not prohibited from air shipment. Gel batteries use a thickening agent like fumed silica to immobilize the electrolyte.

AGM batteries were originally developed for use in aircraft. In AGM batteries a fine fibreglass mat between the lead plates absorbs and immobilizes the acid. This makes the acid more available, enhancing the reaction between the acid and the plates. Consequently AGM batteries can be discharged and recharged at higher amperages than other types of construction [1]. They are also resistant to vibration, operate in any position and will survive submerging.

Gels and AGMs have a lower internal resistance, losing only 1-3% per month due to internal discharge. Gel cells lose 10-16% to heat during charging while AGMs lose as little as 4%, meaning that the charging system can be smaller.

All of these types are built in different physical sizes. The most appropriate size for a boat’s starter and house banks is 8D. Types cannot be mixed in a house bank, because they have different discharge and charging rates. In fact, all batteries in any battery bank (not just on a boat) should be of the same brand, type and size and, preferably, batch number. Lifeline, Optima® and Rolls Surrette are typical AGM brands.

Lead battery lifespan is reduced at temperatures over 77 F, so put the batteries low and as close to the keel as possible to keep them cool. It is a good practice to have the house bank fused internally as well as externally. This will keep a battery gone bad from shorting and discharging the entire bank. Some batteries are built so you can replace individual cells.

Layout

There is a lot of discussion about whether you should have one or two separate house banks. The idea behind two banks is that you also have two separate charging systems, thus there is good redundancy in the system. But it is clear that for maximum electrical efficiency and battery life, you should have one virtual house bank [2]. One house bank also satisfies Occam’s razor (see Chapter 2). If necessary, this virtual house bank can be divided into two physical banks to better distribute weight.

The exception is that you could put a separate battery in the Pilot House, for all instruments and emergency lights. Normally, it would be in the charging circuit for the house bank, but in an emergency it could be switched out and isolated using a fail-open relay with a manual bypass switch. In an emergency, this will preserve communications and navigation instrumentation independently of other demands.

The major disadvantage is having to run long heavy-duty cables from the engine room to the pilothouse. The distance will not be too long with a midships engine room, but an aft engine room could require 40-50 ft of cable. In this situation, you are strongly advised to plan for a 24-VDC or higher system.

Bilge pumps may be wired directly to the batteries, and if so, are provided with in-line fuses. The battery banks are fully metered.

Each engine fitted has its own starter battery, and a 1-2-Both switch that will allow it to be started by either start battery or, in an emergency, the house bank.

Capacity

When you have determined the Total Daily Load in AH, multiply it by the desired Charging Interval (days) to determine the Battery Drain Between Charges. Once a day seems like a common-sense choice. With less than a day, there will be a tendency for charging cycles to run into each other, along with all the extra fuss for your neighbours at the anchorage. With more than a day, you will need an ever bigger and more expensive house bank and alternator. With once a day, you exercise the system every day, keep the engine from rusting out, produce minimal fuss, and keep battery and alternator costs in a reasonable range.

Basic layout of the house bank: (a) engine starter, (b) house supply, (c) instruments, (d) 1-2-both switch, (e) isolation switch and/or fail-open relay

There are several approaches to determine the House Bank Required. A common one is to size the bank so that it cycles between 50% and 80% charged. Using this approach, you would simply multiply the Battery Drain Between Charges by 333% and throw in a 15% fudge factor for good measure, i.e., multiply the Battery Drain Between Charges by 350%.

However, batteries are constrained by their discharge/charge rate. For example, flooded-cell batteries cannot discharge at a rate more than 25% of their capacity. A better way is to base the size on the discharge/charge rate of the selected battery type. For a flooded cell, you would apply a factor of 400% to determine the total capacity required. (Refer to Table 8-1 for a working example.) For gel and AGM cells, you could go as low as 300%; although in all cases more battery is better than less. The resultant is the House Bank Required.

Divide this number by the AH rating of your chosen battery type, to determine the number of batteries in the house bank. Typically, for a passagemaker under 65 ft, the house bank will have four to ten 8D deep-discharge batteries with a capacity of 1,100-2,800 AH.

Alternator

Each engine (if there is more than one) has a high-capacity dual-output alternator and multistage regulator, with separate charging circuits for the starter and house batteries. The charging sources (alternators, trickle and charger) are automatically switched. A backup manual switch and regulator are provided. The regulator must be suited to the type of battery: Flooded cells require an equalization charge after the main charge; whereas gel and AGM cells usually do not. Typical vendors are: Ample Power [3], Balmar [4], Ferris [5], Hehr [6], JackRabbit Marine [7], and SALT [8].

Sharina is designed to be left unattended for a week. So to keep the batteries charged at least one engine must autostart.

The Charging Factor determines the required capacity of the charging system (see again Table 8-1). This rate of charge will damage the battery if it is too high. If it is too low, the batteries will be chronically under charged. The rule of thumb is to charge a deep-discharge flooded-cell battery at a rate of 25% of the listed AH. A gel cell can be charged at 40%; while an AGM can take an unlimited charge.

To determine the Basic Charging AH, multiply the House Bank Required in AH by the Charging Factor. To this, add the battery load while charging, i.e., the Fixed DC Load, Fixed AC Load and Other DC Loads. This total gives you the Required Charging Capacity AH. The larger this is, the bigger and more expensive the alternator required.

Finally, we need a reality check. How long will it take each day to re-charge the batteries? An hour would be nice. Several hours would be insufferable, and counter-productive. To determine the daily charging period, divide the Battery Drain Between Charges by the Required Charging Capacity (other loads net out). In the example shown, a flooded cell bank will take 55 min to charge, a gel cell 34 min and an AGM cell 28 min. Obviously a gel or AGM is the way to go, provided you can manage the larger alternator and charger system. Remember that these times are for a hypothetical house bank of 1100 AH capacity. A real example is likely to be several times larger.

Trickle Charge System

In case the main charging system fails while Sharina is unattended, a DC trickle-charge system is provided. Trickle charging is also a good idea because there are usually parasitic loads on a battery system that will slowly discharge it. Deep discharge batteries do not want to be trickle charged at a high rate: 3% is recommended. Thus a trawler with a house bank of 1000 AH requires a trickle charge of 30 AH.

Table 8-1 House Bank Calculation - Example
Line	Item	Amount	Calculation	Comments
A	Total Daily Load AC AH	200		Normalize to 12 or 24 V
B	Total Daily Load DC AH	50		Normalize to 12 or 24 V
C	Total Daily Load AH	250 A+B
D	Charging Interval (days)	1
E	Battery Drain Between Charges AH	250	C*D	Amount to recharge
F	Battery Efficiency Factor	1.1		Typically 90%
G	Charging (Safety) Factor %	400		Use 350-400+
H	House Bank Required AH	1100	E*F*G
I	Battery AH	275		Use the AH rating of selected battery
J	Number of 8D Batteries	4	H/I
K	Battery Capacity	1100	I*J	Reality check in case H and K are not equal.
L	Charging Factor %	33		25% is the norm for flooded cell; 40% for gel cell; 50+% for AGM
M	Basic Charging Rate AH	363	K*L
N	Fixed DC Load AH	5		Load while charging
O	Fixed AC Load AH	50
P	Other DC Load AH	0
Q	Required Charging Capacity AH	418	M+N+O+P
R	Time to Charge Hours	0.7	E/M

Wind turbines and solar panels are ideal for a trickle-charge system; although they are not suited as a main power source.

Unfortunately, as a main power source, each of them has a significant performance drawback in the context of a small- to medium-size long-range trawler. They simply need too much real estate.

Air X Marine wind turbine – Photo with permission © Northern Arizona Wind & Sun, http://www.solar-electric.com/

For traditional horizontal-axis wind turbines (HAWT), the drawback is the size of the rotor, the noise they make, low efficiency (25-40%) and the constant output. As a main power source, you would need a propeller the size of a house. To be economical, commercial wind turbines need an average wind speed of 25 km/h.

Vertical-axis wind turbines (VAHT) are more efficient (43-45%) and scale better, but not available yet in marine models.

But for trickle charging, a 400-watt HAWT like the Southwest Windpower AIR-X produces a maximum of 33 AH, just right for our house bank of 1000 AH [9, 10]. The catch is that the AIR-X has a noisy 46-in rotor whizzing above your head. Larger units have comparably larger rotors. Rotors can be made smaller if the turbine is engineered to turn faster, but this requires a stronger wind. Wind turbines make noise when they flutter, and sometimes they growl. They have to be mounted as high as possible, and produce vibration.

They are active generators, producing power whenever the wind blows. If the batteries are fully charged, the output of the turbine must be diverted somehow, e.g., to a water heater or some other electrical system.

They also have no output when the wind stops. Denmark invested in 6,000 wind turbines on the national grid, theoretically providing 19% of demand. But they have to keep conventional plants running at full capacity in case the wind drops.

Water turbines, like the Ampair Aquair 100, are also available. But these are designed primarily for cruising sail boats [11]. They use the energy from the forward motion of the boat to turn the turbine. Since in a powerboat the engine generates that forward-motion energy, a water turbine doesn’t make sense. It’s better to mount the generator on the engine directly.

Because of the real-estate constraint, solar panels can’t provide primary power either. This is too bad because the sun delivers around 1000 Watts per square metre at the surface of the earth. A 100% efficient panel 5 x 2 m would deliver 10,000 Watts (833 AH). But commercial solar panels are only about 13% efficient with an optimum sun angle. A trawler needing 1000 AH at 12 V would need more than 100 panels on a barge as a primary power source.

For a trickle-charge system, solar panels are less intrusive than a wind turbine. Unlike turbines, solar panels are passive devices. They produce no current when they are disconnected.

So both wind turbines and solar panels are suited for trickle charging the house bank. Because of their passive nature (no noise or vibration, no moving parts, no active current) solar panels are a more elegant choice. They are also lightweight, easy to install, clean, low maintenance and have a long life. Their disadvantages are limited power, poor performance on cloudy days, and no performance at night.

Most solar panels from 5 to 120 Watts are 12 V, the rest up to 200 W are 24 V. After that, you’re into units designed for tying into the electrical grid. A single high-efficiency 125-W solar panel like the Kyocera KC125G measures 56.1 x 25.7 x 2.0 in (1425 x 652 x 52 mm), and outputs 7 AH while the sun is up [12]. Note that ratings are given for one peak sun hour at 25 C so performance deteriorates at off-peak hours and with temperature changes. Peak time is noon, when the distance from the sun to your location is the shortest.

In our simplified example, a house bank of 1000 AH, a trickle charge of 30 AH would need four of the above panels. On a trawler with a beam of 15 ft (180 in), you could mount six 25-in wide panels side by side on the boat deck or on the flybridge roof, if it had one. This would yield around 42 A for, say, an average of 5 h/day, or 8.75 AH per day. The most efficient way to use this is with a linear-shunt regulator as follows. If the battery is:

• Under load, feed the load directly
• Discharged, charge it
• At rest, trickle charge it

There are three common panel technologies: single-crystal silicon, polycrystalline, and thin-film amorphous cells. Single-crystal silicon cells are rigid and expensive to manufacture but provide the greatest efficiencies and have a stable output during their lifetime. Polycrystalline cells are also rigid, cost less but have lower efficiencies. Thin-film amorphous cells are inexpensive to manufacture, but are not as stable as single crystal or polycrystalline cells. Amorphous panels are made in rigid or flexible panels with the flexible panels costing a bit more.

Solar panels range from 5 to 200 Watts output in full sunlight
– Photo with permission © Northern Arizona Wind & Sun, http://www.solar-electric.com/

An interesting new solar technology is PV-TV, a semi-transparent coating for windows. Developed by MSK Corporation, it passes 10% of visible light while generating 38 W from a 1-m x 1-m window [13]. It provides shading against excessive sunlight, reduces solar gain, gives UV protection, and acts as thermal insulation. It also works as a rear-projection display screen at night (if you want to use your windows as a billboard). To produce a 30-AH trickle charge we would need 10 such windows on the sunny side.

Other improvements are coming. Researchers at the University of Toronto have developed a flexible plastic panel that is 30% efficient [24]. It operates in the infrared spectrum. Nanosolar has developed a printing process to make rolls of thin-film solar cells [26]. In July 2007 the New Jersey Institute of Technology also announced a polymer process to print sheets of carbon-nanotube solar cells. Other companies in Europe, China and Japan are racing to develop thin-film technology.

Any selected solar panels should have a rigid frame, and be designed for marine use with a floating ground. For maximum efficiency, they should be mounted perpendicular to the angle of the sun. In practice, it is best to mount them flat at a 10-degree angle and forget about the complications of tracking the sun. Most rigid panels have an aluminium frame, which must be isolated from a steel hull. The panels should clear the deck by at least 1.5 in, to allow circulation of cooling air, and be free of any shade.

Mounting them at a small angle allows rain to run off. Consider a mount that lets you adjust the angular setting, depending on seasons, latitudes and moorings. Note that fungus tends to grow where the frame meets the panel.

Panels should be fitted with individual inline over-current fuses, to protect against ground faults. Each panel should also be fitted with a bypass diode, to shunt the panel if it fails or is shaded. The overall solar system should also be fitted with blocking diodes, to prevent reverse currents from the battery to the solar cells at night. Some installers are concerned that the resistance of fuses and blocking diodes reduces the available voltage during the day. This is less of a concern in 24 V systems than 12 V ones [14].

The AC Secondary System

The ship's secondary electrical system is AC. In Europe it will be designed for 230-VAC single phase. In North America it will be either 120-VAC single phase or 240-VAC double phase. A manual switch in the Pilothouse selects "boat power" (inverter) or "shore power" as the power source, with automatic detection of the voltage and frequency of the shore power. In the boat, the green AC ground wire is connected to the Common Grounding Point – the white ground wire is left floating. AC wiring should be stranded copper, not solid or tinned, to better resist breaking from vibration. All AC light bulbs adjacent to metal, especially in the engine room, are protected as shock hazards. All AC outlets are equipped with ground-fault-circuit-interruption (GFCI) circuit breakers.

Inverter/Charger

A combination inverter/charger is attached to the house bank for generating AC when offshore, and/or charging the batteries from shore power when in port. Points to consider in an inverter/charger are:

• Peak power output
• Peak charging current
• Continuous charging current
• Battery size AH
• Output voltage
• Output current regulation
• Safety factor of 30%

Sharina’s design requires an inverter with a capacity of about 7,000 W, which is high by normal standards for this size of boat. However, Sharina’s design goal is not to provide the minimum for casual use but to provide at-home comfort at all times.

Shore Power

Because Sharina is intended for passage making, she has to operate on shore power almost anywhere in the world. To do this requires voltage conversion and frequency conversion.

AC voltage conversion is readily done with a transformer having multiple taps that can step-up or step-down a range of voltages. For a specific input voltage, the corresponding tap is selected manually or automatically. The transformer then delivers the correct output voltage.

This fits well with best practices. Although there are several ways of bringing aboard AC, the best way is an ABYC-approved isolation transformer between the shore power inlet and the breaker panel. This avoids polarization issues and doesn’t require a reverse-polarity indicator. AC shore power is brought aboard through an electrically isolated marine-rated receptacle in the side of the Deckhouse. A multi-tap isolation transformer meets this specification.

The incoming AC is grounded (green wire) at the shore end but is not grounded to the hull.

Frequency conversion may or may not be critical. Most modern electronic equipment is designed for 50-60 Hz, and should operate without difficulty (check the label).

The problem areas are timing devices that reference the AC, microwave ovens and AC motors, including those in domestic refrigerators. AC motors designed for 60 Hz will run more slowly on 50 Hz, and tend to overheat. To avoid this, you can:

• Use DC motors only.
• Put AC motors on the inverter power only, not on shore power.
• Install a voltage- and frequency-converting inverter/charger.

Sharina’s approach consists both of using DC motors only and a voltage- and frequency-converting inverter/charger. The design objective of her electrical system is to run as much as possible off the DC primary system. Vendors include: ASEA, Atlas, Charles Industries, Failsafe Power, Magnus Marine, Mastervolt, Stored Energy, Olsun, Xantrex [15-23].

An example of a controller for the electrical system
– Graphic with permission © Ample Technology, http://www.amplepower.com/

Controller

The controller in our scheme is a single point of failure, so a backup controller or a bypass system should be provided.

Distribution Panel

The AC/DC distribution panel is located in the pilothouse. Remote latching relays disconnect the batteries in the event of an electrical fire.

Summary

An efficient electrical system can be designed to run for a day off a house bank. A separate genset is not required. The design maximizes DC services while minimizing AC. The charging period is around one hour per day. The preferred DC voltage is 24 V, with solid-state DC-DC converters for 12-V equipment. There is a single house bank with a high-capacity dual-output alternator and multistage regulator. Trickle charging is solar. Shore power uses voltage- and frequency-conversion for global compatibility.

References

1. DC Battery Specialists, http://www.dcbattery.com/agmtech.html

2. Boatowner’s Mechanical and Electrical Manual, Nigel Calder, McGraw Hill, ISBN 0-07-009618-x.

3. Ample Power, http://www.amplepower.com/

4. Balmar, http://www.balmar.net/

5. Ferris Power Products, http://www.charternet.com/greatgear/hamiltonferris/

6. Hehr Power Systems, http://www.hehrpowersystems.com/

7. JackRabbit Marine, http://www.jackrabbitmarine.com/

8. Sea Air Land Technologies, Inc., http://www.salt-systems.com/

9. Southwest Wind Power, Inc., http://www.windenergy.com/

10. Power Performance Test Report for the Southwest Windpower AIR-X Wind Turbine, National Renewable Energy Laboratory, NREL/TP-500-34756, September 2003, http://www.nrel.gov/docs/fy03osti/34756.pdf

11. AMPAIR Natural Energy, http://www.ampair.com/

12. Kyocera, http://global.kyocera.com/

13. MSK Corporation, http://www.msk.ne.jp/english/company/

14. Blocking Diodes and Fuses in Low Voltage PV Systems, John C. Wiles, Southwest Technology Development Institute, and David L. King, Sandia National Laboratories, Presented at the 26th IEEE Photovoltaic Specialists Conference, September 29-October 3, 1997, Anaheim, California.

15. ASEA Power Systems, http://www.aseapower.com/

16. Atlas Energy Systems, http://www.shorepower.com/

17. Charles Industries, http://www.charlesindustries.com/

18. Mastervolt, http://www.mastervolt.com/

19. Olsun Electronics Corp, http://www.olsun.com/

20. Xantrex Technology, http://www.xantrex.com/

21. Magnus Marine, http://www.magnusmarine.com/

22. Stored Energy Technology Limited, http://www.set.gb.com/

23. Failsafe Power, http://www.failsafepower.com/

24. Ted Sargent, Nature Materials, January 9, 2005, http://www.nature.com/nmat/

25. Glacier Bay, http://www.glacierbay.com/

26. Nanosolar, http://www.nanosolar.com/