How many Arbys is that? :-)
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From: "Steve" <sstuller@netzero.com>
To: <electricboats@yahoogroups.com>
Subject: [Electric Boats] Re: Proper battery capacity
Date: Wed, Apr 17, 2013 6:17 am
Another guide for figuring out your battery capacity is to use your average boat speed. Assume three knots then given a six hour day and borrowing Eric's data for a power input of 100 watts per ton of displacement (at three knots) and 50% DOD then you have 600 WH/day/ton/.5 or 1.2 KWH of battery capacity per ton. This is the capacity of a 100 AH 12 volt battery or one battery per ton. Using Eric's boat as an example you would have 1.2 KWH/battery times five tons or six KWH of battery capacity. That's reasonably close to his actual consumption. Thanks. Steve S.
--- In electricboats@yahoogroups.com, "Eric" <ewdysar@...> wrote:
>
> Hi Arby,
>
> That seems like a good starting place. I am running an 8kWh lithium pack in my 10,200 lb ketch and I rarely get down to 50% of my usable capacity (I use 80% of rated capacity for my usable capacity) during my typical day sails and weekends of coastal cruising. To get the same range from other battery types at 4kts, I would need 11kWh of AGM or 13kWh of flooded cells. So averaged out, that's pretty close to 1 Wh per lb like you suggest.
>
> Of course, special use cases would require different size banks. But I think that typical recreation sailboaters will do fine with your rule.
>
> Fair winds,
> Eric
> Marina del Rey, CA
>
> --- In electricboats@yahoogroups.com, Arby Bernt <arbybernt@> wrote:
> >
> > We have a nice rule of thumb for power, about 1kw per ton of displacement.
> > I'd like to propose a battery standard.
> > How does 1wH per pound of displacement work?
> > Our test boat, a 7000lb Ericson 27 has 9600wH, and is never worked. A 13000lb Rawson 30 I converted has 12kwH of power, and it gets worked.
> > Other Systems..?
> >
> > Arby Bernt
> > Advanced Marine Electric Propulsion.
> >
>
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