Fair comment. Don't have numbers for an atomic 4, but engines from that
period were typically below 20%.
-----Original Message-----
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com]
On Behalf Of Eric
Sent: Wednesday, 4 August 2010 5:48 p.m.
To: electricboats@yahoogroups.com
Subject: [Electric Boats] Re: hull design
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 A bit out of date with thermal efficiency.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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