Advice on gas/electric hybrid.

I am working on a design for a 27 ft sailing dory. I am thinking of a solid steel centerboard and a center cockpit, under which the centernoard is located/hidden. I want to have auxilliary propulsion, but wish to use the entire aft cabin are for accomodations.
The six foot long area under the cockpit is entirely free except for the centerboard case. My thought is to offset the case several inches. On one side (here the dory has a 4 ft flat bottom, lowest point in hull), I want to locate a gas generator of modest size (3000 watts, 4 hp, etc.). This would be an off-the-shelf item----removable, replaceable, fan-fed at all times, exhaust carried to point above cabin roof.
The offset centerboard would allow a shaft to pass directly on centerline all the way forward to the forward cabin. The companionway of the forward cabin would be offset to the side to allow the electric motor to sit at knee height in full view. Batteries would be located opposite the genset, low down
and close to centerline. An hour of run time might need four batteries.
The idea is to keep weight centered, low and out of the way. Losses due to generation and motor would be acceptable given that the gas engine could run at moderate rpm even while topping out, at least for a couple of hours.
Motor would be 120 volt able to run at about 100 volts--- batteries would be series wired, 24 volts times four (actually probably yielding over one hundred volts or more at full charge--- otherwise, five batteries would be fine too.)
DC capable 120 volt motor then.
All this allows engine to be independantly located, and centerboard essentially centered. Charging could be done by prop as well while underway by sail, with the motor serving as generator.
Concerns are: Higher voltage, reliable bilge air exchange, and efficiency.
Imagined advantages are: 120 volt lighting and tool power, low voltage cabin option, engine to side without prop to side, motor in cabin for access and drier environment, exchangability of genset cheaply at any time, amd quiet operation for harbor maneuvers and reliability of power when needed to instanly reverse or power out of a situation.
Unknows are related mostly to electric issues regarding motors, batteries, controllers, etc., not to mention possible economic issues.

Feedback would be appreciated. It is probably wise to go for a marinized small diesel genset with low voltage output, but I'm not too familiar with pricing, cost/benefit, etc..

Alan

 

http://www.hondapowerequipment.com/gen.asp

 

what kind of dc or ac motor are you going to use? Dc motor hp?controller?

 

That's my question. I want high efficiency, high enough to compete with a normal engine/gearbox. I am in the process of working out what motor/controller would be best, and at what voltage.
The engine gains efficiency by running at peak efficient RPM whenever running----- and also by eliminating the gearbox.
A diesel genset with 10hp would be ideal, and would easily fit to one side of the centerboard. The batteries opposite would balance the engine weight.
The question of AC or DC is dependant on several factors. If AC, I can run direct to motor if AC/DC, but can't store power in the batts without an inverter.
I may be stuck with a DC generator, but would like the voltage to be high (120 at least) for the motor.

Alan

 

Alan
My experience with salt water and electrics is that they end up high maintenance but the experience is mostly limited to low power lighting and instrument circuits in boats under 30 feet. You seem to be well aware of the problems.

I cannot offer any proven boat systems but I did find this site when trolling around looking for nice boat size motors:
http://www.electricmotorsport.com/PARTS/parts.htm
I thought the pricing was very good compared to others I have priced. I expect these would be durable designs but would need special care to avoid corrosion issues on a small boat.

I suggest a brushless motor with the full 4-quadrant drive as this avoids one item of maintenance and will also allow you to recharge from the motor when under sail. Will kill sailing performance in light wind though if you try to charge then.

You can get electric motors with different degrees of protection (weatherproofing) even submersible but the costs go up. Baldor is a brand of DC motors that comes to mind. However I think AC motors with 4-quadrant drives would be my first option with any voltage.

Once you get into higher voltage systems the risk of electrocution goes up and the engineering requirements become more demanding. You will probably not find a 48V generator that is cost competitive with a standard voltage unit so you will need a charger that takes normal AC input and nominal 48V output if you go for this voltage. There is one at the bottom of the page on the link that might be suitable.

Rick W.

 

http://www.asmomarine.com/2005/asmo_uk/00.shtml

 

When did I miss this comment? Thanks, Rick. I appreciate the info.

Alan

 

Interesting. I'm glad to see this is commercially viable. I like the idea of solar panels. That and a wind generator, and also prop generating, ought to provide all that's needed, meaning the genset would hardly ever have to run if I had enough batteries.

Thanks

A.

 

You really will need a good charge controller to get the most from your batteries. It is really easy to damage batteries with overcharging and undercharging. You do not need to have 120 volts in batteries to get 120 volts AC either, the charge controller will do that for you with the magic of electronics.

 

And I'm just guesing, a charge controller is not cheap?

 

I'm not sure what their price is for a boat. In solar photovoltaic home systems, they run a few thousand dollars for the smallest systems. But they are intelligent controllers that charge a battery as fast as they will safely accept the charge, not overcharge, and the voltage output to the batteries doesn't have to be the same as what you are using the electricity at.

 

Thanks. I've considered running a hybrid system and charging a small bank of batteries from the prop while underway. The prop shaft would be direct to a motor/generator, and a genset would supply surplus current to the batteries. The prop would turn the generator when desired and do the same.
The simplest system would do away with the genset entirely, and all recharging would be from the prop to the motor/ generator. This is essentially the same as any common engine charging system except there would be a larger battery bank (enough to provide an hour at cruising speed).
It seems that a gas or diesel engine to the side of the prop shaft (belted to the shaft) would be the better solution.
I don't want to spend so much on controllers and complication when what I really want is to sail most all of the time and motor for such short periods that I can do so electrically, with that current coming from the prop while sailing. I might have a variable pitch prop, in any case, to maximize the charging aspect without slowing the boat too much.