T-Pain Is On A Boat: Re: [Electric Boats] Proper battery capacity

Monday, April 15, 2013

Re: [Electric Boats] Proper battery capacity

It's still sounds like a good metric, just that there are classes of boat-use that need to be factored in.

Motor power / boat mass (specific power of the whole boat) and (usable, not nominal) battery capacity / boat mass (specific energy storage capacity of the whole boat) allows us to plot drive systems and storage systems from many different boats on a simple 2D chart. I expect clusters will appear and these clusters will indicate the different use-cases, whether cruising, work-boat, club-racers, trolling bass-boats, etc.

You could also look at the ratio of capacity to motor power. As it falls below 1:1 (smaller battery banks), you will want to look for onboard charging sources -- whatever the method, or shorter trips between shore-charging.

The typical rules-of-thumb for systems on this list revolve around 1kw/tonne motor power and 1kWh/tonne battery capacity for most conversions.

There are exceptions to either side of that, but I am willing to wager that these deviations have reasoned use-cases behind them. And I believe that all of these use-cases will form distinct clusters in the above-proposed chart.

Such a chart would very likely help keep things in perspective for the prospective convert, and go a long way to helping them make an informed choice.

/Jason

On Apr 15, 2013, at 11:16, Carter Quillen <twowheelinguy@yahoo.com> wrote:

I can testify that 5000 Whrs is grossly inadequate for a 40,000# boat.

My dream is for two of those 20 kWhr Li Ion fork lift batteries packs for $20,000 but budget reality will probably force me to just get another 8 pack of Trojan T-125s for $1000 which will be twice as good as what I have now but still inadequate. I think I would be good with a total of 20 kWhrs of storage though, which is .5 Whr/# in my case. However I get about 25 kWhrs/day from my solar panels which definitely factors into the equation. So if you're operationg strictly off your batteries, 1 Whr/# is probably a good benchmark to shoot for but if you have another energy source such as solar or a genset, I'd say 1 Whr/# is a bit heavy and the .5 Whr/# is a more like it.

That's just my opinion and I would also add that's when it comes to energy storage capacity, more is always better.

Carter

From: Arby Bernt <arbybernt@yahoo.com>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Monday, April 15, 2013 2:51 AM
Subject: [Electric Boats] Proper battery capacity

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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