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In a message dated 12/23/2004 10:52:30 A.M. Eastern Standard Time, Alec.Smyth@compuware.com writes:
Snoopy was built to the original K-250 plan, with the side thrusters and a rudder, but no rear thruster. The side thrusters work great, but the boat has insufficient speed for the rudder to have any perceptible effect. I'm considering removing the rudder and replacing with a stern thruster, but another option would be to leave the existing rudder in place, and cut a piece out of it to mount the thruster in. hopefully that way I'd still have the use of the rudder when being towed, and also increase the effectiveness of the rudder if the thruster prop wash is flowing past it. Of course doing this cutout job is more work than just putting in a third thruster. What d'you guys think, would it be worth the extra trouble? Add the thruster to your live rudder--it can't hurt, and will definitely be a help from time to time. At slow speeds, the rudder would work better with a thruster in front of it, as it would be giving you "faster" water, as it were, to direct left or right. Even so, the rudder needs to be sizeable. Perry subs used a 12" X 36" rudder behind a 36X36 three-blade bronze prop (on the PC-12s and up) and even then, at slow speeds, we had lateral thrusters fore and aft and a vertical mounted on the bow. The big wheel would kick you around pretty good with a big shot of power, but for slow speed maneuvering, we used the little kickers. Same thing as the dive planes. All the Perry's had them, because they work, or assist, and any edge you can get that would save a little power was worth trying. Keep in mind, we carried over 2-tons of batteries in a standard boat, and 3-tons in the big boats. I spent many an eight-hour day on the bottom, and we don't have to do that with our psubs. Thank your lucky stars for that!!!
Just to illustrate some of the differences is instructive. My three Kittredge thrusters all in a pile weigh less than the Perry main propeller--which went 175 pounds, as I recall. We used a Reliance 10hp motor designed for SCRs and reduced it to about 300 revs through a gear box, which then attached to the shaft and seal package (which cost $10,000 all by itself). You didn't want to stick your finger in there to try and stop that prop, I'll tell you that.
Something to ruminate over through the holidays.
Merry Christmas,
Vance
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