Hi Michael,
Always glad to help get another electric boat on the water.
On the charger question, I was referring to some of the modern multi-channel, multi-stage, "smart chargers" that are on the market these days. While you can buy a 48V charger to charge all 4 batteries in series, there is a tendency for the batteries to get out of balance over time, especially if they are not loaded evenly. By using a separate charger for each battery, this effect is eliminated. Here are a couple examples:
http://www.dualpro.com/store/items/2/4/
http://www.marinco.com/product/20-amp-dual-battery-chargepro-charger
The dual pro has 4 isolated channels, basically 4 separate chargers in one package. The Marinco (Guest) has two channels so you'd need to buy two of them. I've used that particular model on two installations so can vouch for them. I've heard positive things about the dual-pro but no personal experience. There are some others on the market I'm sure. Just make sure the outputs are isolated. Some multiple output chargers have a single negative lead and won't work for series-connected batteries. If the specs say "12 and 24V" for a dual or "12-24-36-48" for a quad it should be OK.
Regarding motors, I was assuming you were going for a low-cost DIY type installation hence the desire to use a golf cart motor. I've never done such a conversion personally, but I still think it would be a reasonable approach if you don't need a lot of power, are handy with machinery, and can find a good deal on the components.
The Briggs and Stratton E-Tek was a nice permanent magnet dc brush motor but is no longer sold, though I sometimes see them (or clones) on E-Bay out of China. Mars makes some popular PM Brush motors with the same mounting pattern and similar power ratings. I'm not familiar with all their various models, but lot's of folks on this group are using them. I ran one in my Albin 25 last summer. Power ratings start at more than double the golf cart motors I was talking about previously, but if you want to really use that power you'd need bigger batteries. Even so, if you run a 5HP motor at 1/2 power it will be more efficient than running a 2.5HP motor flat-out. The bigger one will last longer and run cooler, plus you'll have extra thrust for maneuvering when you need it.
You're correct that DC brush motors don't need a controller to run, but I would advise against doing your installation that way. The "lower" batteries will always be discharged more than the upper ones. Discharged batteries have a higher internal resistance so they will limit how much amperage you can draw from the upper ones. Also, if you ran the lower ones way down then tried to run full power you'd actually be "reverse charging" the lower ones. Don't know exactly what would happen then, but it's not a good scenario. Plus you'll need a big-ass switch and there will be a lot of arcing and sparking going on. A little too "Frankenstein" for my taste, though it might be fun if you're into that sort of thing. You could mount 4 big knife switches on the bulkhead and really have some fun!
But seriously, it's better to use a controller. In the unlikely event of a controller failure, you can always bypass it and limp home.
Brushless motors are the next step up in power, efficiency, and cost, but I'll leave the discussion of pros and cons to someone else.
On the reduction drives, If you go with one of the bigger motors as discussed here, a single vee belt probably isn't going to cut it, and you're probably going to want a little less reduction. Most seem to be between 2:1 and 3:1 but it will depend on your particular battery/motor/prop combination. If you design your mount to accommodate that range you should be able to dial it in once you get it running.
Regards,
Jim
--- In electricboats@yahoogroups.com, shea1719@... wrote:
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> Thank you Jim for your informative reply. You have answered so many questions so very clearly that a good picture is beginning to take shape in my mind. Which leads me to some more questions, of course.
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> 1)   I have been informed that the preferred motor for this application is the ETEK face mount configuration, brush type. The advantage, besides the obvious (easy face mount, and no need for an additional external bearing to support the stub shaft, as well as no need for an expensive spline section), is that you don't need a controller, just a high amperage tap switch (I am including a PDF of the schematic diagram).  I kind of like this approach, except that it seems that the #1 battery gets the lions share of the load. Or is it that the batteries still drain evenly since they do remain all connected together. In non-technical thers, the voltage seems to be 'filtered' through the #1 battery (or #1 & #2, etc), limiting voltage to the sum of the number of batteries selected by the wwitch. Anyway, can you (or anyone else) try to explain how this works? Can you (or anyone else) perhaps discuss the advantages and disadvantages of the brush type motor vs the brushless type with the controller??
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> As far as the V-belt approach, as well as your 3:1 reduction estimate, I was already on that page. It's good to hear that other folks also favor that approach.
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> Lastly (for now), just what is meant by a "four-channel" charger??
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> Thanks, Jim for your clear information. I hope that you (or someone else) can answer these other questuions!!
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> Regards -
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> Michael Shea
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> ----- Original Message -----
> From: "luv2bsailin" <luv2bsailin@...>
> To: electricboats@yahoogroups.com
> Sent: Wednesday, March 16, 2011 2:50:01 AM
> Subject: [Electric Boats] Re: Columbia 29 sailboat
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> Michael,
> I think most golf cart motors are in the 2 to 3 HP range, which would would probably get you 3 or 4 knots and plenty of maneuvering thrust. Used as aux power for motor sailing it could be very effective. I'd be looking at the higher end carts, say 3HP and preferably 48V.
> You're going to need a reduction drive to match the motor to the prop. Taking a wild guess I'd say 3:1 would be a good starting point.
> I like belt reductions because it's easy to play around with ratios to get it optimized, and they are quiet. In that power range you could probably get away with a vee belt, especially if it's a good quality "CRE" type. They're much cheaper than the timing belts used on many of the higher-power installations, though maybe a wee bit less efficient.
> Most of the GC motors I've seen bolt right onto a differential and have a splined shaft. Once removed from the differential there is no shaft support bearing, so you'd need to come up with a way to support the output shaft. Also need a way to adapt the splines to a pulley hub. Could probably just turn the splines off and use a compression hub. None of that should pose a big challenge if you have access to a machine shop.
> As for power requirements, 3HP is 2238 Watts, which boils down to about 47 amps on a 48 volt system. If you went with 4 group 31 deep cycle wet-cell batteries (typically 100 Amp Hours), you would want to limit your runs to less than an hour at full power. Cut back to half power and you could do 2 or 3 hours. Better batteries will do better of course, but I'm assuming you're looking for an economical solution. For charging I'd get a 4 channel marine smart-charger of 10 or 15A per channel.
> Jim McMillan
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> --- In electricboats@yahoogroups.com , "ComcastMail" <shea1719@> wrote:
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> > I have a 1964 Columbia 29 sailboat with a 47 year old gasoline Atomic 4 engine. I don't motor much, I sail. I don't like the engine. I only need it primarily to get in and out of the marinas & harbors, and occasional ill winds. I am on a large inland lake where the winds are usually very favorable. I think that a golf cart motor conversion would be ideal. I'm a mechanical engineer, so designing the installation would be pretty easy. I just need to learn more about the electrical system, performance, battery drain, etc. Have any of you ever utilized a golf cart system to power a sailboat? I am happy to be in the group..
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> > Thank you -
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> > Michael Shea
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