T-Pain Is On A Boat: Re: [Electric Boats] Propulsion Marine 5 KW Electric Drive

Tuesday, October 26, 2010

Re: [Electric Boats] Propulsion Marine 5 KW Electric Drive

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@gmail.com>
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@yahoo.com.au> 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@yahoo.com>
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@yahoo.com.au> wrote:

From: Rob Johnson <dopeydriver@yahoo.com.au>
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@toolboat.com>
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