John-
With 4000# and 20' waterline, you're not looking at needing huge amounts of power. My 26ft wood barge cruiser is about 4000# & 19' waterline. I have powered this with a now old "Etek" 8HP brush motor for going on 11 years now and have only burned thru about half of one set of brushes.
If weight savings is key, the 55# minimum motor weight Mike mentions is more than 2x what you could get away with---my 8Hp motor is nom. 20#---much lighter than the 60# series-wound motor I started out with. I agree with much of what Mike says below.
Initially when I converted my outboard to electric, I started out with 6 golf cart batteries (36v), later expanded it to 2 strings of 6 for what should have been 300-400ah practical. Since my batteries weren't prime, my range wasn't as good as I had hoped. Later, I retired those batteries and went with just one string of used golf cart batteries for several years, using my genset whenever going any big distance. Most recently, I've retired the lead acid and now use 2 surplus Lithium modules in parallel, for a total capacity of 140ah at from 48 to 30v. These 2 modules weigh maybe 160# together and take little more space than a couple of golf cart batteries. I'm still working out the details for this system in terms of charging, cell balancing, disconnects & etc. In the meantime, I'm very pleased with the performance of lithium and am happy I went there even though it was a $2600 expense and even though so far it's a cobbled together 70ah single-module setup. The very cool thing about going electric is you can easily upgrade to new technology as you go along. It took less than 6 months of use before I decided that the 60# motor had to go in favor of the 3x lighter B&S Etek. I also upgraded my controller pretty quickly also. Batteries, chargers, BMS, DC:DC, etc…all upgradeable.
There are all sorts of safety and performance considerations that are important, so heed the advice of folks on this forum about cabling, protection devices, etc.
-Myles Twete, Portland, Or.
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of mike@electricyachtssocal.com
Sent: Sunday, January 19, 2014 11:45 AM
To: electricboats@yahoogroups.com
Subject: [Electric Boats] RE: lower voltage batteries
John,
This is Mike from Electric Yachts of Southern California. You listed the benefits of electric conversion for you:
Easy of installation, this is with all the plug and play systems.
Weight, this varies according to the selection from about 55 pounds to about 200 pounds for the motor. Battery packs with from 100 pounds (LiFePO4) to 250 pounds (AGM's) - do not recommend flooded for your boat. I do not see needing 245AH 8D batteries (see projections). You can push your boat with either a 36v or 48v system with ease.
Speed and Power (hull speed <6kts) (range 80% DOD)
480w 3.1kts with 100AH AGM battery bank 24NM
960w 3.9kts with 100AH AGM battery bank 14NM
1920w 4.9kts with 100AH AGM battery bank 8NM
2880w 5.7kts with 100AH AGM battery bank 6NM
A small portable generator will drive at over 3kts with the right charger
Easy of use, with a small boat like the Stone Horse the electric is simple, instant, less stress the boat, and more convenient to use.
I am not sure what is meant by the "split configuration". Are you thinking of having the batteries pack built with a significant run between the batteries? If so, that is not a good way to do it. The batteries should be only separated with modest cables lengths and the cable must be marine grade,well constructed, and aproperately sized.
The big question is "Is it still an experiment". Not really. The issue is that the diesel became the defacto system in the 1970s and therefore still prevelant. The same for the ICE in the car industry. Today would you consider the hybrid to be "experimental" likely not. Would you consider the all electric "experimental", maybe? It really is a feeling because as far as I know there are very few diesels the do not have electric starters (very dependable), electric fuel pumps, alternators, and electronic controls. IMHO, for a small boat like yours the idea of the diesel noise, vibration, and fumes would keep me from enjoying the boat to its fullest.
Mike (somewhat biased)
Electric Yacht of Southern California
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