John,
We have a 50' powercat with twin 135hp Perkins.
Displacement about 36,500lb.
We have also researched electrifying her.
Our stats are, for both motors running:
1500rpm, 7kn
1900rpm, 9kn
We have also done some calculating power off the Perkins engine curves:
1500rpm = 30hp each engine, so 60hp gives 7n
1900rpm = 50hp each engine, so 100hp gives 9kn
But if we use one engine only, we find that:
1850rpm, 7kn and 46hp from the power curves.
So actually only 46hp is needed instead of 60hp that the theoretical engine curve gives.
46hp = 34kW.
So possibly 2x20kW motors (which are rated less if continuous duty) would be enough for 7kn.
We also had Oceanvolt do an independent analysis. Some of those people who have taken that path have said that the OV analysis was very close to what they subsequently got, so we have good trust in their data.
For us, OV came up with a battery draw of 30kW for 7.4kn, but only 21kW for 6.2kn and 8.5kW for 5.1kn.
So if 5.5kn is acceptable, we could get away with a 20kW generator (peak, continuous again is less).
Some of the best we've read about are the DC gens of Eniquest in Australia, and if we go down that path that's what we'll use.
We are now contemplating a parallel hybrid though, keeping the Perkins for faster needs and adding 2 x 10kW (peak) motors on the shaft via belts, possibly clutched. We had hoped someone like Hybrid Marine in the UK could help but they don't modify on existing motor setups.
The motors, batteries and controls are pretty easy to find nowadays, but we can't yet find a way to mount and attach to the drive shaft with bodgying up something (always an option!).. The Italian transfluid system looks interesting but pretty complicated!
On 10 Apr 2019, at 7:26 am, oak oak_box@yahoo.com [electricboats] <electricboats@yahoogroups.com> wrote:
Robert
On 10 Apr 2019, at 7:26 am, oak oak_box@yahoo.com [electricboats] <electricboats@yahoogroups.com> wrote:
I'm looking at buying a 38' trawler that currently has twin 135hp Perkins diesels.Hull speed - 8.2 knots / 9.5mphWeight - about 20,000 poundsSpeed at 1000 RPM on both engines is about 5 mph, at 1500 RPM is maybe 6.5? Max RPM should be around 2500.I don't have the spec for the props.Just as a mental exercise (brain fart...) - how ridiculous would it be to convert this to a hybrid electric?The thought would be to pull the two diesel engines, replace with electric motors - very possibly AC? And drive them from a generator.Could I drive both engines with a reasonably sized self contained Honda generator? (I would think certainly at slow speed...)It seems like it might be a little easier (and significantly more efficient) if I skipped the battery bank (I'd never be able to afford a big enough one anyway) and just connected AC motors directly to an AC generator.It would still get me away from two huge diesel engines, and eliminate all the through-hulls, pumps, etc...Honda makes 5KW generators for about $3K... And a 9KW generator for $5K.I suspect it probably isn't practical, but thought it might be an interesting thought to propose.I know someone on the list converted a 40-ish foot Chris Craft - but still uses batteries, and only goes a few mph.I'm wondering how fast I could get if I had a 5KW generator or even 9KW generator driving it....Though even with 9KW, that would still be only 4KW per side (and probably not constant load).And then there's the reality that a Honda generator probably isn't intended to be used on a boat in a salt water environment (an inland lake environment would probably be pushing it...).But just as a thought - could I get large enough AC motors that can be speed controlled to work driving a boat?John
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Posted by: Robert McArthur <rjmcarthur@gmail.com>
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