[aerohead]

1) We'd need the fineness-ratio for their 'strut' .
2) That would allow us to find it's 2-D drag coefficient for the 'stalk' portion.
3) We could probably come up with the 3-D drag coefficient for the motor housing easy enough, which isn't any different from a typical electric trolling motor.
4) And, say, the 'frontal area' of the higher 2-D Cd cylindrical 'strut' for a conventional electric trolling motor would be 'smaller' than for their lower drag streamlined strut, so it's frontal area would have to be ascertained.
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I would prefer that the 'battery' be in the boat, and 'shrink' the dimensions of the submerged streamlined strut to it's structural minimum.
And there may be more hydrodynamically efficient 'propeller' designs.