Re: Screw size and speed

[VBra676539@aol.com]

In a message dated 7/16/99 10:03:04 PM, shawl@torchlake.com writes:

<<The most costly part in my entire main drive unit was the ceramic face shaft
seal at around $80.00 new. The big 3 blade brass prop was something a diver
friend found on the bottom of a lake. And another friend that had a prop
service made it as good as new, polished it and everything. He figured it was
worth about $400.00 at that point, but it cost me zero. >>

For what it's worth, I've used both styles, and however good the new, 
rare-earth motors in the 1 to 2 hp range, I still prefer the big wheel. Perry 
boats turned 36 X 36 3-bladed bronze props (they weighed 175 pounds!) that 
were driven by 10 hp 120V Reliance motors through reduction gears and 
controlled with SCR packages and produced over 600 pounds of thrust (that's a 
900 pound bollard pull, calculated down, and don't ask me how they do it).

The 12-boats would stop in their own length from a knot and a half or so and 
they weighed 8 tons. Figure on spending more and carrying more weight if you 
want one, as the whole rig probably weighed over 500 pounds. The shaft seals 
were crane 12-springers and there were a pair of them with bearing sets and a 
mounting flange and an inch and a quarter shaft. The seal package cost $10K 
or so as I recall, so $80 ain't bad, all things considered. The smaller boats 
turned smaller wheels, but not by much. Both PC-14s, for instance, used plain 
old 36 volt golf cart motors. 5000 rpm if memory serves with 17 to 1 gear 
reduction. They turned a 28 X 24 bronze wheel and ran nearly 5 knots on the 
surface. 

And either one of them would sure pull you off a dock if you were silly 
enough to hold onto the rope. And a lot more besides. 

Vance