Diesel Electric - practical?

[richardandtracy]

In general I agree with Paulka.
The addition of extra equipment has the effect of dropping the usable energy at the prop, needing a larger/ more expensive/ less efficient installation. I may quibble a bit about the electrical efficiencies of generators/ motors (nearer 90-95%), but even so it's still not good news.

Also think of the added complexity. With a diesel, you have to worry about the engine & fuel. With the suggested installation you've still got the engine & fuel, but you've added unreliability by including a battery storage system, motor and generator too. Their individual component reliability may be high, but its still going in the wrong direction. The simpler systems are usually more reliable.

Now, if someone could come up with a motor like the new ones in washing machine outer drums, where it's entirely encapsulated in plastic and so has no need for hull penetrations I'd go for it like a shot, and ignore the extra inefficiency. Having no underwater holes through the hull would make me very happy.

Regards

Richard.


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[pvb]

It\'s not a myth in this case...

I mentioned the pleasure of manoeuvering silently in a marina, and it would be quite feasible to do this using just the batteries. Half a ton of batteries gives you quite a bit of silent power!

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[oldharry]

Re: It\'s not a myth in this case...

Agreed if you have room for a half a ton of batteries! Power to weight ratios start coming to mind here....

Come to think of it though, are not the side thrusters fitted to larger stinkies electrically powered? Is there not scope for adpating one of these units someway?

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[spark]

Nick,

There are valid bits in most of the arguments for and against above - I have heard and considered them all over the last couple of years while researching the desirablity of electric drives for sailing boats.

Early on I went to Solomon Technologies but was scared off by the price/bulk/weight of their electric motor, to which they are committed (having developed the thing and struggled to find an application for it).

After much research we have decided to develop our own system (which I won't detail here for fear of transgressing the rules of the forum), the prototype of which will be tested this winter.

The diesel/electric concept works well for larger yachts that typically carry a drive engine and a genset. For your own boat I'd still argue that it is viable.

The power required to push a boat through the water rises geometrically with speed. For example, our prototype boat has a theoretical hull speed of 6.6kn with a calculated drag (in flat water) of 915N. The drag at 5kn is only 250N

If you are happy with a cruising speed of c. 75% of your 'hull' speed then you can use a diesel genny with a power rating of c. 50% of a drive engine (which must be powerful enough to drive you at full speed). For the occasions when you need an extra burst of power (e.g. manouevring or getting out of the way of a bigger boat) the battery bank will provide the extra oomph.

We are going down the DC motor route for simplicity and cheapness. The only maintenance issue is brush wear - easy and relatively cheap to replace.

You will need to have room below the waterline for a battery bank to give you a useful DC voltage (possibly 120V in your case) without compromising the stability of the boat. We have designed the batteries into the boat as ballast.

If you keep the boat on a pontoon and typically go from marina to marina, sailing as much as possible, there is an argument for increasing the size of the battery bank and doing away with the genset. The shore power can recharge the batteries overnight. A portable suitcase genny can be carried as a backup to get you home if the batteries are getting low.

If you want to discuss this further please email me - mh@qei.co.uk

Malcolm

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[vyv_cox]

Re: It\'s not a myth in this case...

They are certainly not silent. One of the loudest and most intrusive sounds in most marinas.

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[Coppershield]

I agre with ccscott49

Hi, I agre with Colin, conseder hydraulic system If i understan correctley you want to youse the generator. Most gensets in your boat size will not have the nesesary output but thet can be overcome and then run a properley sized electrick motor power hydraulic pump in turne thet will power the hyd. motor and prop.this is only a outline you will also need controll sys. filters, heatexchage and more.
However, I have sean Solomon tech. is work two years ago this month nice guys. but the system at the time wase small (10 to 15 Hp I thinck). ps conseder Yanmar (No relasion).
Goooood luck
Muzaffer


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[ccscott49]

Re: It\'s not a myth in this case...

It's not the motor, thats the problem, it's the prop cavitating and ventilating. Different than an aft prop, as you know.
But I would go the hydraulic route, then you can have a hydraulic bow thruster, anchor winch, genny, all run from one soudproofed engine, mounted in the best possible position for weight distribution with almost silent, water split exhaust system, heaven!. Could even have the genny running on the engine direct or for real belt and braces, a seperate genny, for electrical loads, with a small get you home, manouvering hydraulic pump, soundproofed of course.

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[jonjo]

Re: Diesel Electric Narrowboats

Some narrow boat owners are doing this, see:

http://www.nb-whisper.com/design.html

http://homepages.cs.ncl.ac.uk/harry.whitfield/home.formal/Elektra/engine.html

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[oldharry]

Re: It\'s not a myth in this case...

I know - I often wondered why they have to be quite so harsh?

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[NickCharman]

Re: An american solution?

My boat is 43' - displaces 13.3 tonnes. Currently a Perkins 4-108.


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[NickCharman]

Many thanks....

I am really impressed with the range of sites I've been given to look at. The views are all helpful, and I suspect that while this technology may be possible, it will be a trade off of price and performance for silence, and possibly reliability.

I now have some reading on the topic.

Really interesting stuff.

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