Hi James,
Have you conducted drag tests comparing a given diameter prop with a corresponding diameter bucket? That sound like something I'd like to try (unless you have already done it).
Can you give us a comparison of power regenerated when using the two props you mentioned?
Thanks!
-Tom
--- In electricboats@yahoogroups.com, James Lambden <james@...> wrote:
>
> When you have an electric boat you have to make a decision whether or
> not you want to be hooked into nature's energy.
>
> Having a big prop does exactly that. A big propeller turning slowly
> adds enormously to the efficiency of the system, perhaps twice as
> much in the case of Kapowai going from a 12x 6 to a 12.5 x 14.
>
> A big prop also increases regeneration. Regeneration is directly
> proportional to size and shape of the propeller.
>
> However, it does come at a cost, and that cost is sailing speed with
> the propeller not turning. It will slow the boat down as much as a
> bucket dragged behind the boat of the same diameter.
>
> With Kapowai, we have a 20 KWH battery bank so it could run at zero
> thrust for over 200 hours. Ultra-efficient drives, have very low
> phantom loads, making this possible.
>
> One 200 watt solar panel aimed at the sun would more than compensate
> for the energy required to zero-thrust the propeller over a 24 hour
> period.
>
> An additional 200 watt solar panel, aimed at the sun, could add an
> additional 1 knot of boat speed over a 24 hour period.
>
> James
>
>
>
> On Oct 26, 2010, at 7:16 PM, Rob Johnson wrote:
>
> >
> > JC , I would have to answer YES to both questions , thus I believe
> > having the e-motor on , under sail , would be a big advantage.
> > Regards Rob J.
> >
> > From: Joao Carlos d'Almeida <joaocarlosdalmeida@...>
> > To: electricboats@yahoogroups.com
> > Sent: Wed, 27 October, 2010 12:05:54 PM
> > Subject: Re: [Electric Boats] Propulsion Marine 5 KW Electric Drive
> >
> >
> >
> > Does a larger prop create more drag when the e motor is not on? And
> > will this slow down a sailboat very much?
> >
> > JC
> >
> > On 26 October 2010 16:33, Rob Johnson <dopeydriver@...>
> > wrote:
> >
> >
> > Yes , so I thought.
> > I've used the diesel on my boat to motor sail , and while it allows
> > me to gain a couple of knots , and point a little higher low revs
> > for a long period of time is not good for the diesel .
> > But should be ideal for the electric motor , I believe.
> > I've just this minute got the pricing though on a hybrid setup ,
> > the price has doubled , over the diesel alone.
> > I guess I'll wait , its sure to come down.
> > Regards Rob J.
> >
> > From: Daniel Michaels <nov32394@...>
> > To: electricboats@yahoogroups.com
> > Sent: Wed, 27 October, 2010 10:00:07 AM
> >
> > Subject: Re: [Electric Boats] Propulsion Marine 5 KW Electric Drive
> >
> >
> >
> > It will usually make sense to use the electric drive while sailing.
> > It takes very little power.
> >
> > Dan
> >
> > --- On Tue, 10/26/10, Rob Johnson <dopeydriver@...> wrote:
> >
> > From: Rob Johnson <dopeydriver@...>
> > Subject: Re: [Electric Boats] Propulsion Marine 5 KW Electric Drive
> > To: electricboats@yahoogroups.com
> > Date: Tuesday, October 26, 2010, 4:10 PM
> >
> >
> >
> > Just to go off on a tangent slightly.
> > Assuming we have a motor sailer with a hybrid diesel of 50hp
> > diesel , and 10hp electric .
> > Under sail , wouldn't we get maximum value from the electric
> > motor , turning the large prop ?.
> > The motor isn't so much driving the whole show , as contributing ,
> > and instead of there being prop drag , there is prop drive .
> > What I envisage is an electric drive contribution for most sailing
> > time .
> > Does this make sense ?.
> > Rob J.
> >
> > From: James Lambden <james@...>
> > To: electricboats@yahoogroups.com
> > Sent: Wed, 27 October, 2010 6:49:02 AM
> > Subject: Re: [Electric Boats] Propulsion Marine 5 KW Electric Drive
> >
> >
> >
> > Dick,
> >
> > That would be true. More propeller area means less propeller
> > slip and higher efficiency.
> >
> > However, you can accomplish the same thing by having a larger
> > propeller turning slower. ( A larger propeller will require a
> > higher reduction gear ratio )
> >
> > James
> >
> >
> >
> >
> > On Oct 19, 2010, at 10:34 AM, Dick B. wrote:
> >
> >>
> >>
> >> Jim:
> >> You said:
> >> < < However, as an electric drive consumes more power, the
> >> thrust per kilowatt decreases. This is because the propeller gets
> >> less efficient the faster it turns, which is a result of more
> >> propeller slip. Also, the electric motor becomes less efficient as
> >> it creates more power.>>
> >>
> >> This would indicate that a more efficient electric drive system
> >> to power a boat would be to have several motors running at a
> >> fraction of their max output driving several peopellers turning at
> >> slower speed. Is this true?
> >>
> >> Dick
> >>
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
>
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