Screw size and speed

[Michael B Holt <michaelbholt@juno.com>]

I've been looking at the pictures of the Hunley.   It had a 30-inch screw
that turned at . . . a low speed, I would think.

I see other small subs with a pair or more of smaller, higher-RPM screws.

It's my understanding that it's fairly easy and inexpensive to buy what
seems to be large trolling motors as power.

But is there an operational reason small high-speed screws are used?

Why can't a large low-speed screw do the same thing?  



Mike Holt
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