Bill,
Any idea who makes those Les Schwab batteries? If they are from a decent manufacturer, that is a great deal. I will need another set or two in the spring, so I'll do a little snooping also and report back if I learn anything.
Back to the original poster's question regarding gear reduction, most likely you'll need to gear it down a little. If you can design your setup so you can change out the pulleys/sprockets you'll be able to dial in the ratio by experiment. Roller chain and sprockets are pretty cheap but noisy. Regular old vee belts work too up to a few HP and are also fairly cheap. Buy one big sprocket/pully and an assortment of small ones if you want to experiment. If you have a "Tractor Supply" or some such local farm store they'll likely have everything. Otherwise McMaster Carr has a good selection.
For inboard displacement hulls in the 20 to 30 ft range the reduction ratio is commonly in the neighborhood of 2:1. For an outboard you'll have to take into account the lower unit ratio plus the fact that the prop is likely on the smallish size. I don't know how to calculate it accurately, but if you know the prop pitch and do the math for "miles per rev" etc, factoring in your target speed to get target RPM, and put in about a 50% slip factor, you might get in the ballpark.
With the trial and error method, you simply start with your best guess and then play with the ratio until you find something that keeps your batteries out of trouble at full throttle, as indicated by your amp draw. For GC batteries I like to keep them under 120A or so max, and limit my continuous running to about 50A. That's pretty conservative.
Hope this makes some sense.
Jim
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