The effect of the drag also depends on the boat..I do most of my sailing on heavy displacement full keel boats and they really do not slow that much even in light air..
Richard
--- 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
Received: Tuesday, October 26, 2010, 11:48 PM
Well James , for me , fishing under sail all day , moored on a swing mooring , I'm not going to get much solar energy , or opportunity for mains recharge. So , if I have drained the batteries somewhat , I'd just use the diesel for long enough at the end of the day , to get a recharge.
Solar panels on a boat on a remote swing mooring is vulnerable to theft , using them under sail not so practical . So hybrid sounds good to me , but OH , THE PRICE !. Rob J.
From: James Lambden <james@toolboat.com>
To: electricboats@yahoogroups.com
Sent: Wed, 27 October, 2010 1:46:31 PM
Subject: 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
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