The Comfortable Pocket Yacht 
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Flicka Sailing
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Dual Auxiliary Propulsion This is another one of my pipe dreams where I take a simple and cost effective solution and make it complex and cost prohibitive. In other words, what follows is basically a rant and I will need to carefully examine this before actually trying to use one of these dim witted solutions to a non-existent problem. As I see it, the issue is: how can I get the comforts of some auxiliary propulsion with the least investment in cash and energy from fossil fuels. As a baseline, we should all remember that a human athlete in very good condition can produce work totaling about 0.35 horsepower for extended periods. One author claimed that the world record for human power was an output of 2 horsepower for 6 seconds. Against these standards, the smallest diesel engine typically found on a sailboat produces 9 horsepower. This can be envisioned as being equivalent to having about 25 strong backed men rowing your sailboat. To me, this seems a bit or overkill! As I define it, the problem is that I want to use auxiliary propulsion as little as possible. However, my experience is that internal combustion engines that receive little use will fail to start at the most critical times. Also, if they do start, they will stop for an unknown reason at an equally critical time. In other words, Murphy is alive and well and lives on board a boat. On my Com-Pac 19, I met my goals by using two engines. Mostly, I just needed to motor out of the marina and move out far enough to where I could make sail. On the return, I would sail in close to the marina entrance, drop sail, and then motor in to dock. All of this was accomplished with a 47 pound thrust trolling motor operating at the lowest two (out of five) speed settings only. Using the instantaneous reverse and slow speed capabilities of this motor made docking a breeze. For those occasions where I needed to motor longer distances, I would use a 4 HP Mercury two stroke gas motor. For the following discussion I will assume a Flicka 20 with a cruising displacement of 5,500 empty weight and an additional 1,000 pounds for crew, equipment, supplies, and beer. For those that have waded through my pages on The Math Of Sailboats system , you will know that the calculations show reaching hull speed with an input of about 9.5 HP under water tank conditions (no current, wind resistance, or other excess drag). Likewise, calculations show hat a respectable motor speed of about 4 knots can be achieved with only 4.5 Horsepower. Therefore, I'll assume that 6 horsepower is a compromise that will deliver 4 knots even when conditions deteriorate. Also, the use of 3/4 horsepower trolling motors that deliver about 45 pounds of thrust will be sufficient to move the boat around in a marina situation. In water tank conditions, this motor is capable of pushing the Flicka at about 2 knots. A 4 stroke gasoline outboard engine is the most cost effective solution for auxiliary propulsion on the size boats that I am considering. This engine is relatively cheap and much lighter in comparison to a diesel of similar output. Also, major service is simpler since the engine can be removed and transported to the mechanic rather than the mechanic making a "house call" to the boat in the case off an inboard diesel engine. The down side of the outboard is that the motor is positioned at the transom and the weight will make the sailboat stern heavy. Even with an extra long 25 inch shaft length, the outboard’s propeller is also closer to the surface of the water and will tend to come out of the water in a heavy seas. Outboard engines also do not provide anything like the battery charging capability that is standard with an inboard diesel engine. The down side of the inboard diesel is that the motor, transmission, and propeller shaft must be mounted aft and on the centerline. Additionally, the engine requires sufficient extra space to allow for service from at least one or two sides. More space is also required to provide for sound insulation between the cabin and the engine compartment as well as space for 10 to 20 gallons of fuel in an inboard tank with associated fuel filters and other plumbing. The space used by the engine and it’s fuel tank is therefore some of the most desirable real estate on a small boat. The fuel tank generally takes up space that could be used to make a larger lazarette and the engine takes up space under the cockpit that would be ideal for additional batteries and storage of sails and long term cruising supplies/spare parts. One solution that has been proposed to diesel engine location is to use hydraulic pumps for power transmission. In this model, the diesel could be located anywhere that is convenient on the boat and the power transmitted to the needed location with hydraulic fluid. As I see it, this has potential benefits as far as space utilization, but a hydraulic leak in cramped quarters is not a pretty picture. Also, propeller speed control is somewhat more difficult to achieve with this system. Many years ago, electric propulsion was the desired method for small harbor boats and pleasure launches. This was due mainly to the poor reliability and efficiency of small internal combustion engines of that era. Even today, electric propulsion of small specialty vessels such as research submarines is the only way to go. The down side of even the most efficient totally electrical propulsion systems is the life cycle operating cost of the battery bank, the weight of the battery bank, the low operating range of a battery powered propulsion system, and the cost of the speed control system required to handle large power flows. This is the reality faced by proponents of electric vehicles of all types, cars, boats, and light weight airplanes. With regard to a sailboat, it is of course possible to design an installation where the batteries replace the necessary ballast for the boat so that the total vessel weight does not get out of hand. A Flicka 20 for instance already carries 1,500 pounds of lead in it’s keel. Expressed as battery equivalents, this is about 30 golf cart batteries and could supply 180 volts DC to a motor. With the above assumptions, I would expect the 6 HP motor in our example to draw about 25 amps at full speed and the most we could hope for is to keep this up for 2 hours without damage to the battery bank. Of course, our time under motor power would substantially increase if we do not run at full speed. The obvious problem is that the boat is not being designed from scratch but I am using an existing vessel. In this case, the weight of the batteries is in addition to the ballast and the space taken up by the batteries detracts from the available storage space. This makes a conversion project unfeasible. Further problems with this pure electric approach are due to the cost of the components. An efficient variable speed control that is capable of handling 180 volts DC is extremely expensive. Lowering the voltage does nothing since the total power required remains the same and controls that are capable of handling high amperage at lower voltages are just as expensive. An alternative is to use switches to use a number of batteries in a series/parallel configuration to provide different voltages to the motor. This is possible at a much lower cost, but not practical for very low speeds since the motor may tend to over heat under these conditions. Solomon Technologies has been trying to market this motor as suitable for use in sailboats. As I understand it, this is a special high torque pancake style DC motor and they have been testing it on a 30 foot sailboat on the Chesapeake Bay. Sizes down to 4 KW are supposed to be available. I will be getting more information on this shortly. The system is designed to use propeller drag to recharge the batteries. (Note - as of July, 1999 I have not had any responses to my inquiries for additional information from Solomon.) If the consumption of power for non-propulsion purposes represents a large fraction of the total energy requirement of a boat, then a hybrid design alternative may become attractive. This is already the case on some larger pleasure ships, cruise ships and some of the more sophisticated Navy ships. In this case, it is more efficient to run one engine at it’s optimum speed and power point for fuel economy and use it to produce electrical power only. The electrical power can then be used for any desired purpose - propulsion, air conditioning, refrigeration, lighting, or recharging a smaller battery bank to provide reserve power or low speed propulsion. Similar hybrid designs are currently being considered in cars where the city driving is battery operated and once out on the highway, the required electrical power is supplied by a generator operating at it’s most fuel efficient speed. For this theoretical sailboat, I would use a diesel generator producing 110 and 220 volts to provide the required power as needed. The generator would power a 6 HP electric motor drive operating as a two speed forward only propulsion system using a clutch and belt drive system. Low speed maneuvering power and reverse power when required would be provided by a fractional horsepower electric motor arranged with a clutch to power the same propeller shaft in parallel. This arrangement is cost effective since a single diesel generator serves for both propulsion and energy production. At low speeds, it is also effective since the stored energy from a small battery bank is used for maneuvering thrust during docking operations. As an additional benefit, the generator does not need to be mounted aft and on centerline. Only the electric motor drives need to be in this position, so the utilization of space can be improved under some conditions. Since the diesel operates at a fixed speed, the diesel engine controls are simpler. In fact, they do not need to even be in the cockpit. Only the electric motor controls need to be in the cockpit. If you really want to get creative, the electric controls can even be remotely operated so that no cockpit control panel is even required. In a sailboat conversion effort, this is only practical if the existing diesel motor power needs to be completely replaced. In this case, a boat could be configured with all the conveniences of home including air conditioning, refrigeration, freezer, and other modern conveniences at little more than the cost of a new diesel engine. If I get an outboard powered boat, I will investigate making a wide motor mount board just like I did for my Com-Pac 19. I will add a salt water series trolling motor to this mount and operate just like I did with the Com-Pac. A 45 pound thrust trolling motor will provide all the maneuvering power I should need in a marina. If I get a inboard powered boat, I’ll bite the bullet and live with the diesel as is. However, if I can get a boat at much lower cost with a "dead" diesel, I will think long and hard about the diesel generator option. This bleeding edge option will certainly make me take it in the neck when I go to sell the boat. But maybe I can still get my use out of it and live in greater comfort than I would imagine. Another alternative that has been used by others is to make a fossil fuel powered battery charger. This is constructed by using a small (2 to 4 Horsepower) air cooled gasoline or diesel engine and running an automotive alternator on the engine with a belt drive. Using a Honda GXH50 2.5 HP engine (at only 12 pounds), this setup might be the most practical implementation that still allows for significant electrical use. The alternator would be limited to a 60 amp type and for ease of installation, should have the newer single wire regulator. Automotive alternators are not known for their efficiency, but this solution is simple to build and does not require a great deal of room. However, even with good mufflers, this is a noisy solution for a small sailboat. Even smaller and lighter solutions can be envisioned. Using a Weed Wacker 2 stroke engine in the 30 cc displacement range, a 35 amp alternator can be driven. These small alternators were common on some import cars from about 1975. The alternators and their mechanical voltage regulators are still available at costs in the range of $50 to $60 complete. The weed wacker engines are often available on clearance tables of your local hardware store or at garage sales. Much has been written during the past two years about the direct conversion Methanol Fuel Cell being developed by the Jet Propulsion Lab and University of Southern California. In principle, this would be the answer to my needs since a 5KW (6.7 Horsepower) fuel cell would convert methanol directly to electricity at temperatures below the boiling point of water. This means no requirement for extensive thermal insulation, no noise, no circulating water coolant system, just a simple feed of methanol and the product is water, carbon dioxide gas, and electricity. Since methanol currently sells for 40 cents a gallon, this seems like a fine solution for a small boat power source. Prototype fuel cells have been running for hundreds of hours without interruption or reduction in output. The energy conversion efficiency of the current fuel cell is above 35% of theory (gasoline engines produce mechanical energy at about 20% of theory and electrical energy with much less efficiency) and scientists believe that 45% efficiency is possible in future versions. Small cells may be available sooner and are envisioned as a replacement for battery banks. A 50 watt demonstration cell (in a 4 x 6 inch package) was produced that required a pint of methanol per day to operate and was intended to produce electricity for military purposes. In 1997, a 150 watt methanol fuel cell was already under development for the US Army. The 40KW cells that would be required for a full size car will take longer to produce but Daimler-Chrysler has already shown a prototype car with hydrogen fuel cells and indicated that the Methanol Fuel Cell would be used if this vehicle went into production. If this technology gets to market in the next five years, then auxiliary electric power for a sailboat will be a "no brainer". The very large fly in the ointment is that the estimated cost of a 40 KW fuel cell would be about $30,000 under mass production conditions. If I can reduce the propulsion power requirements to 1.5 horsepower or less (remember - this is still the equivalent of having 4 strong rowers on board), then an even cheaper hybrid alternative presents itself. A 675 amp hour battery bank (6 deep cycle batteries) can be used in combination with a 200 to 500 watt fuel cell to provide up to 8 hours of operation under motor power at about 2.5 to 3 knots maximum speed. The fuel cell can then continue to operate all night to recharge the battery bank and the system will be available for another 8 hours of motorized travel the following day (as of summer, 1999 - there are rumors of a 250 watt methanol fuel cell to be marketed in the fall by Matsushita). To make this feasible, will probably require a trolling motor with a Kort Nozzle propeller housing design. At sailboat speeds, a Kort Nozzle housing system will increase thrust by approximately 30% with no increase in energy consumption. There is no free lunch, the kort nozzle will reduce efficiency in reverse but this is an acceptable loss since the motor can be turned 180 degrees if really necessary. Of Course this is all my opinion - I could be wrong. Ballard Power Systems Inc. has just announced (09/27/2001) the availability of a 1,200 watt OEM power module under the Nexa trademark. Ballard is only offering the module in OEM format and others will manufacture complete power generation systems based on the module. In the text of the announcement, Coleman Powermate indicated that the Nexa module will be used in a new product to be introduced before the end of the current year. The Ballard module is designed to use hydrogen gas and this might still be the major stumbling block - of course, cost may make this impractical - only time will tell. Additional public disclosures from Ballard indicated that they had provided 133 advance production units to Coleman and 10 other prospective systems integration suppliers. By the third quarter of 2001, Ballard had received purchase orders totaling 1.8 million dollars (Canadian) for production fuel cells. Coleman/Powermate continued to indicate that commercial fuel cells would be available shortly.
This page was last updated on November 25, 2001 06:35 PM |
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Copyright © 1999-2002 Jobst Vandrey |