Tom Mitrukowski, Mark Frasca, et al,
Mark Stafford here really loving this large boat thread. The under 30 foot sailboat crowd deserves credit, but there are advantages for big electric boats too! Just ask the biggest ship of all, the Queen Mary 2 (4 big diesels (90K hp) and 2 slightly smaller gas turbines (60K hp), all combined in various ways to power the 4 big underwater swiveling electric pods.)
I myself am repowering a 55 foot Herreshoff three masted schooner with a 23hp series DC 96-120V GE direct drive with cooling fan and 16 to 20 6volt golf batteries and a three blade 20 inch diameter prop. Adequate, though not ideally efficient... it is just what I've scrounged over the years.
No water data yet.
I pulled out a 50-60hp GM271 (WWII). Fueled motor ratings are theoretical ideals that exclude normal losses like fuel, water, and oil pumps, alternator, poor airflow, used injectors, non-ideal temperatures, exhaust turbine back pressure, water and oil circulation losses, transmission inefficiencies, installation compromises, and perhaps more. The point: my propeller might see 30 hp on a good day with wide open throttle, but probably more likely 25.
Then there is the condition, pitch, and size of the prop, which really makes a difference!
I can get 100 propeller hp out of a 23 hp electric motor, and for more than 10 seconds if I use proper cooling techniques (water coils and auxiliary forced air). Comparatively, a propeller will never see more than 3/5ths of an ICE's rating.
A new friend in Santa Barbara knows more, and has been trying to participate in this discussion, but keeps getting lost in e-hell. James Lambden, a marine electrical specialist and e-boat enthusiast, now has two websites dedicated to rEpowers:
http://www.abovethe
http://www.propulsi
James has been refining a simple geared reduction transmission, as well as sourcing electrical components. He is currently E-powering a 43foot racing sloop and hopes to cover the "up to 100 foot" market.
Carry on,
Mark Stafford
--- In electricboats@
>
> Mark thanks for the input I was about to post a qestion regarding prop size and real world results but I got my answer. If any one else would have any experience with various props on an electric syustem and the results I would appreciate it. I am planning to go to a 16" CDI perfect pitch prop next time the boat is out of the water. My goal is not to go over 40 amps while using the motor and it would be nice to get 4knots at that amp draw.
> Tom
>
> --- In electricboats@
> >
> > Tom,
> >
> > That sounds like a small prop for your boat. I had a fixed 2 blade 11"x10" prop on my Ericson 27 and would get 3knts @ a 20amp draw and just over 4knts @ full power. I changed to a 12"x10" fixed 3 blade prop and now get 4knts @ a 20amp draw and 5.8 knts @ full power.
> >
> > Have you tried different props?
> >
> > Mark
> >
> > -- In electricboats@
> > >
> > > Tom I have a challenger 32' that displaces around 14000 lb. It also had a Perkins 4108. I converted it to electric this year. You can see the pictures in the picture files under the folder Second Wind. I built the rig myself from parts I could get cheap on ebay( with exception of the controller). I used 8 batteries for a 48V system. It should give me 250 amp hours of use. Minus all the losses its probably much less. I think it will run at 40 amps for over 3 hr ( I haven't tested it for this long yet) At 30 amps I get close to 3 knots at 80 amps I get about 4 knots. The prop I am using is a 12" with a 9" pitch and has three blades. My boat ispretty wide with 11' of beem that I think is thre reason for the large amp draw and slow speed. I think your boat will get similar results to mine as far as amp draw is concered and the speeds you can expect.
> > >
> > > Tom
> > >
> >
>
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