I suppose we ought to put some graphs in the files section as this question gets asked quite a lot . The IC motor is rated at its maximum power . Its efficiency is greatest at mid speeds and low at low speeds . so your 50hp will allow you to run (inefficiently) at low speeds and up to plane at relatively high speed. Battery size makes planing speeds impractical for electric boats except over a short range so it is in the low and mid speed range where one should make the comparison.Perhaps to a 30foot boat with a 12 hp motor . The 8hp electric runs comfortably at 8hp and can sustain say typically 12 hp for a period wheras the 12 hp IC cant run comfortably at its rated 12HP.Because of its linear power curve the electric is particulary good at low speeds maintaing torque down to very low revs.
Hope this helps in your understanding . i think viewing the superimposed power curves of the Ic and comparable electric gives the clearest illustration.
Chris S
--- In electricboats@
>
> Hey Dave, I am intrigued at the prospect that a rated 8 hp electric motor
> can have the same pulling power as a 'rated' 50 hp Diesel motor!
> Now I may not understand what "Bollard Pull" is... but I do understand
> that there are a few things people s-t-r-e-t-c-
> is about Gas Mileage and evidently the other one is the power electric
> motors produce. lol. Ok Dave, I'm only kidding but please help me to understand
> how this can happen? I mean 'Efficiency' can only do so much!
> Is this '300 lb Bollard pull' at startup, full speed or someplace in
> between and if this is true, why am I looking at a bigger motor? A 300 pound
> pull is a lot of pull/push...
>
> So let me recap:
> If you took a 20' line and hooked your sailboat (8 hp) to your friends
> sailboat (50 hp) Stern to Stern and you both opened throttle; Nothing would
> move until either you ran out of electricity or your friends sailboat ran
> out of Diesel.
> -Tom- (not my real name)
>
>
> In a message dated 5/27/2009 11:08:35 A.M. Eastern Daylight Time,
> inganear1@..
>
>
>
>
>
> Tom, there are several projects completed and many underway in
> approximately your size range. 48 volt systems seem to be the normal voltage for most
> but some run on 36 volts. Look through the photo section, you'll find
> several to draw ideas from. There are several guys one the site that are
> building a business out of electric conversions making kits/pods and other
> things that may be of interest to you. My boat is a 30 ft ChrisCraft Capri
> sailboat that weighs in at 12000 lbs. I use a Etek brushed motor 8 hp and
> have the same bollard pull as a friend of mine on his 50 hp diesel, (a
> little over 300lbs), so you see it's not just rated Hp that does the job, it's
> also efficiency..
>
> Dave K
>
> --- On Tue, 5/26/09, Tom <_iloveamercedes@
> (mailto:iloveamerce
>
> From: Tom <_iloveamercedes@
> Subject: [Electric Boats] RE: Electric power for over 30'
> To: _electricboats@
> Date: Tuesday, May 26, 2009, 8:15 PM
>
> Hello everyone!
> I know there must be a thread for powering sailboats over 30' with
> electric motors. Can someone direct me to it?
> My sailboat is a Cal 35 Cruising. She is of 15,000 lbs. Displacement.
> I think this project would need around 35 hp. She has a 4-108 Perkins of
> 'Claimed' 50HP hahahaha!
> Anyway, with what little I know about this, I would need a bank of about 5
> Golf Cart Batteries.
> I also want to utilize Solar Panels as well as a Gas Power Generator.
> So let me know how screwed up my ideas are so I can get an idea of where
> to start here.
> Thanks
>
>
> ------------
>
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