T-Pain Is On A Boat: Re: [Electric Boats] Re: does anyone have current real world performance figures please

Tuesday, April 9, 2013

Re: [Electric Boats] Re: does anyone have current real world performance figures please

Another aspect,

I see your point about 1/2 power to save on the slower lower inertia breaking power requirement . BUT when using 2 motors , the second motor props up the first but definitely does not double the mobility. for eg twin motors 2 x 150 hp doesn"t even come close to a single 300 hp . If you add a smaller motor to a bigger one eg a 10 hp to a 25 hp the boat doesn't even know the 10 h p is on the boat. 0 effect . So although economy may be achieved at the lower end using 1 of 2 motors expect to loose big time at the high power end. I have spoken ... Lol .

On 2013-04-08, at 5:22 AM, Carter Quillen wrote:

Eric,

Please explain why having two battery banks is going to cause a loss of power out due to the Peukert's effect. Perhaps I don't understand what your meaning is when you say "the same bank split in two" because it seems to me that if you put two banks in parrallel, you would reduce the amps by half on each bank. My understanding and experience is that the harder you pull on your battery, the less power you will ultimately be able to get out of it. So it then seems to reason that if you had two banks of batteries in parallel, say two 4 packs of 12V, you would get more power than with one 8 pack of 6V of cmparative weight and capacity, because if you needed 40 amps to run your motor, the two 12V packs would be drawing down at 20 amps each but the 8 pack of 6V would have to supply the 40 amps total. This would also allow you to charge them slower and get the same energy into them in the same amount of time two smaller chargers instead of one big charger. I thought charging slower is better too?

I'm thinking we're not talking about the same circumstance but please clarify in case I'm just missing some facet of Peukert's effect here as it relates to a battery's size or something.

And by the way, can any say how to pronoun "Peukert"?

Carter

From: Eric <ewdysar@yahoo.com>
To: electricboats@yahoogroups.com
Sent: Monday, April 8, 2013 1:57 AM
Subject: [Electric Boats] Re: does anyone have current real world performance figures please

Hi Dan,

To me, it sounds like your plan is unnecessarily complicated. Electric motors are fairly efficient at low power (see my measured performance at 3kts, i.e. 50% hull speed). So a single motor, driving through an efficient reduction will do just about as well as what you are suggesting. I don't know the efficiency specs for a v-drive, but you may notice that on page 4 of Julian's posted pics, the author states that gear boxes should be avoided because they are not efficient. I believe that he is referring to typical marine gear boxes, and if so, I would agree. However, my Browning gear box is 98% efficient, which is difficult to match with belts (Goodyear NRG drives are one of the few belt drives that can consistently boast a 98% efficiency), regular v-belts range from 90-98%, with most operating around 95%. Chains in an oil bath may also reach 98%, but exposed chains often degrade quickly.

Some people here that run 2 equal sized battery banks for "redundancy", they give up range due to Peukert's effect, a single bank has greater range that the same bank split in two. But if one believes that the loss to Peukert's is justified by the protection against catastrophic failure of one of their battery banks, then it might be worth it, but not to me. Likewise, your two motors will lose more through two reductions than a single properly sized motor running through an efficient drive, even before throwing in he v-drive. At least, that's the way it looks to me. That said, your plan will work, just not as efficiently as other, simpler systems.

Fair winds,
Eric
Marina del Rey, CA

--- In electricboats@yahoogroups.com, "dan.randolph" <danlrandolph@...> wrote:
>
> Hi Eric,
> Thanks for all your excellent information and advice in this group.
>
> In this post you commented that V-drives may have a loss of efficiency.
>
> I am curious, as I am considering a V-drive, with two small motors (it seems that for most of my use I only need less than 1/2 the power available, with only those "bad" times when full power would be good to have). One way I have considered is a V-drive with one fixed belt to one motor, and one motor on a belt that can be engaged with a gear for when needed. The smaller motors are more efficient at very low amps, for moving at 1/2 hull speed or less.
>
> Thoughts and critiques of this plan appreciated.
>
> - Dan
>
> ---

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