Diesel/electric in small boats

[kulas44]

Has anyone looked into a small turbine to power a generater for this application. They are available in almost any power output one could need and are very well suited to generater usage. Almost no vibration. useing a 480 volt 3 phase genset and apropriate sized 480 volt motors for the load, coupled to variable pitch props would do away with the need to convert to d.c. for motor speed control, and all of the associated electronics. I suppose one could use a standard genset, but piston engines are inherently ineficient and turbines can be very eficient if operated in there proper zone. 480 volt generators and motors would be the easiest and most available units to use, they can be rebuilt or replaced cheaply anywhere and are smaller in size for the power output than 120/240 volt. You could use a stepdown transformer for the 120 volt loads (a.c., lights, pumps, etc.) The most expensive part would be the props. Thoughts ???

[sdowney717]

so with a variable pitched prop you control the speed of the boat. This means the engines spin at a constant speed. How do you go in reverse?

[sdowney717]

Oh, perhaps the pitch allows for this.

[kulas44]

Exactly, the prop takes the place of a gear box, not as much energy loss, lighter, infinitely variable, in a sailboat it can be feathered to reduce drag, lots of positives. The biggest problem with the diesel/electric hybrids is the motor controls and a.c. to d.c. conversion, every step loses energy to heat. I have not seen a setup like I am describing used in a boat but it seems logical. Useing my old tub as an example, it has two 140 hp. diesels and a 15 kw. genset, that all takes up lots of space, weighs about 3500 to 4000 lb.s, and uses a lot of fuel to go real slow, about 9 knots cruising speed getting 2 m.p.g. I could junk all of the old iron, install a 100 k.w. genny with 2 50 hp. electric motors and Helseth or Saab v.p. props, lose a bunch of weight, gain lots of space, get better fuel economy, and most important, it would be much quieter. Hopefully someone with more sense than me knows why this is not a good idea. I haven't done the calculations yet to determine the optimum genset size and motor power but that shouldn't be to difficult.

[crawdaddyjim50]

I would look at using a philips style stirling cycle engine as your genset driver. Very quiet, very few moving parts, can be built robustly, flat tourqe curve, stable rpm, can be run using any heat source.

[Dan McCosh]

Commercial airliners use gas turbine gensets. Problem on a boat isdownsizing--there aren't any really small gas turbines made. The thermal efficiency also goes down with size, which is another problem.

[Clan Gordon]

Apart from the problem of finding a small enough gas turbine, there are a couple of other problems.

1) why does your boat have two 140hp diesels - do you need 280hp to make the speed you need when your boat is heavy laden in a head sea/wind ? If the answer is YES, then two 50hp electric motors are not going to be much use to you. If the answer really is NO, then you could change out your heavy old iron for two 50hp diesels and keep your 15kW genset (or generate your electric power off your diesels). Or just operate the boat with one of the engines ?

2) if the diesel and propeller are well matched for the speed at which you operate, then the diesel will burn less fuel per hp-hour than a gas turbine. Especially since your turbine will need to be bigger than the diesel to produce the same power at the propeller (since there are more losses in the electric transmission chain than in the direct drive)

if you really want to operate your diesels at their optimum RPM regardless of ship speed, you could give THEM a present of a controllable pitch propeller.

There are a lot of diesel engines around in many power/RPM combinations and it is easier to get one that JUST matches your needs. With gas turbines, even Boeing have to design their planes around the standard engine sizes offered by the major suppliers.

At a particular design point a controllable pitch propeller is LESS efficient (because of bigger hub etc) than a simple fixed pitch propeller designed for that speed/revs/power. The CRP is of course more efficient than the fixed pitch away from that design point.

[ 01-01-2006, 09:16 AM: Message edited by: Clan Gordon ]

[Cuyahoga Chuck]

I'm not up on current turbines but those fuel burning tubines of long ago were noted for their ability to gulp vast quantities of air thus producing a lot of heat and a lot of noise which poured out of an extrememly large exhaust pipe.
For a turbine to be acceptible in a modest sized pleasure boat it would have to be as friendly to the occupants as the alternative recip motor.

[Thad Van Gilder]

dumb question, but...
Wouldn't you be just a little worried about that kind of voltage on a boat?

-Thad

[kulas44]

I was an oilfield electrician in a previous life, and a lineman after that. Secondary voltage to 960 was just everyday stuff back then, I worked on transmission lines up to 138,000 volts barehanded, but most of the time I worked with 7200/14,400 volt distribution lines so no 480 doesn't scare me, you do need to pay attention but no more so than the 144 volt d.c. being used on other systems, it'll all kill ya !!!

[sdowney717]

Ballard Power now has a kerosene fueled FUEL CELL.

http://www.ballard.com/be_informed/about_ballard/news/2005/12/19/NOC%20Release

Personally think this is where it will eventually go even with boats. A fuel cell generates the electric power on demand for the electric motors to turn the props.
Power will be quiet, ultra smooth, no vibration and no polution and very efficient.
And lots of onboard electric power for whatever other needs onboard.

[Thad Van Gilder]

I agree. I have been looking at a methanol powered fuel cell from europe for juice production on IVY.

They are production units, and are not that expensive. I'll try to find the link...

-Thad

A good friend is a retired union electricitian who worked in the nuc. plants on that hard core voltage... he doesn't worry about it either...

[kulas44]

I must admit a case of pure ignorance where fuel cells are concerned. I have read a little about the methanol units and a few years back it looked like propane cells might be a viable source of power for residential consumers in remote areas, but I have no idea how they work. Probably, if technology increases they will be a great power source for boats.