Cool. It's fun playing. I have to say though that there comes a point with the kind of motors and sail boat sizes discussed where direct drive once over say 1.5kW continuous measured at the battery; well then it simply makes sense to gear at 2:1 for example due to copper losses and prop choice and go up on voltage, for example from 24V nominal to 48V. I'm with you on series not parallel with lead by the way.
Direct brushed drive as I have, has its place but to my mind only as a low powered sailing auxiliary if not geared. That is to get myself in and out of harbour with a little additional range. In my case about 15 to 20 miles @ 4 knots calm conditions, with a small Honda genny as backup (cheaper than decent AGM batteries). My primary propulsion is my sails.
Only other thing I note is you have a stuffing box. I use a PSS shaft seal, the later types with a hose spigot. This is really handy in terms of efficiency and as I have a garden hose adaptor on the end of the breather hose, this allows me to hook up a low pressure marina water supply and test motors and shaft alignment whilst on the hard.
Bottom line is it all comes down to how much continuous power you actually need for your preferred cruise speed and range combination, with sufficient short term higher power that one feels comfortable with subject to the type of boat and area of operation.
John R
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