Kerry,
While I know that giant supercharged 2 stroke diesels like the ones found in oil tankers and container ships regularly exceed 50% thermal efficiency and the latest gasoline vehicle engines that have been tweaked for milage and emmissions are in the 35% neigborhood at peak thermal efficiency, we're typically talking about repowering older boats in this group. What do you think the thermal efficiency of the engine that is in or came out of you latest boat is?
I doubt that the 1990 8hp Nissan outboard laying in my yard ever hit 30% thermal efficiency. On the other hand, the 1974 Yanmar SVE12 that used to live in my ketch has a manual that lists the best fuel consumption at 1900RPM and 7HP (crankshaft) at about 200g/HP.h. With 5250W produced from 15,200W of diesel fuel, the thermal efficiency of that old thumper peaked around 34%, though it was closer to 30% at the 2600RPM that I typically cruised at.
But you raise a good point, since ICE are still improving in efficiency and electric motors don't really have much room for improvement, without advances in energy storage, electric conversions are harder to justify against current engines than against older ones.
I've tried to work numbers that are representative of many of the conversions being discussed here. By showing my process, anyone here should feel free to do their own calculations that more closely represent their specific situation. If you're pulling a TDI diesel out of your boat to switch to electric, you'll have to use different conversion ratios to accurately estimate your motor and storage requirements than if you're replacing an atomic 4.
Fair winds,
Eric
--- In electricboats@yahoogroups.com, "Kerry Thomas" <kjthomas@...> wrote:
>
> Hi
> A bit out of date with thermal efficiency. Gasoline engines are around 36%
> and diesel from 40% to nearly 60% for very large engines.
>
> -----Original Message-----
> From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com]
> On Behalf Of Eric
> Sent: Wednesday, 4 August 2010 11:47 a.m.
> To: electricboats@yahoogroups.com
> Subject: [Electric Boats] Re: hull design
>
> .... Gasoline engines typically operate at a thermal efficiency of 20-30%. A
> hyper-efficient engine at an optimum setting would do better and an engine
> at lower throttle will do worse. I usually use 25% thermal efficiency in my
> estimations of gasoline engines because that seems like a reasonable
> average....
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