[PSUBS-MAILIST] hard cans vs wet ones

[VBra676539@aol.com]

I thought I'd stick some facts in with all the conjecture here, just for fun.

Perry subs did not, repeat, did not compensate their thruster motors. That means hard cans were used to 3000 fsw, every day. We used a stacked seal arrangement--two crane carbon faced rotating seals, one operating in an oil flooded housing compensated with a simple arrangement of tygon tubing, and the second seal rotating on the back of the secondary seal housing in sea water. This double seal arrangement, which is no more complicated than dealing with internal turbulence and what-not, was all but invulnerable within their tested pressure range.

Hyco, on the other hand, aimed to operate deeper from the start, and developed in-house the Hymak motor which was a serious 5 hp work horse designed to operate immersed in oil. I think we used garter springs for seals, but I'll have to dig the file out to be sure.

Harbor Branch has been using the same thrusters for 20 years and when we were limited to operations at a maximum of 2000fsw, we use plain old o-rings and changed them out after x-number of operating hours as a part of the continuing preventative maintenance program and we rarely, and I mean VERY rarely, had a problem with them. Nowadays they operate to 3000 fsw and have gone to a single rotating carbon on ceramic seal in place of the O-rings.

K-subs use carbon to ceramic rotating seals (just one) in up to 600 fsw plus test depth and they are good for a good bit beyond that.

And I think Phil's Deep Workers are using hard can motors, too, but I'm damned if I can remember so don't hold me to it.

In all instances save the Hymaks, the motors are in pressure resistant containers and operate in air. If the things are designed and crafted properly, they work very well that way. Period. This is not surmise or guesswork, folks. This is fact. I've used them and worked on them and cussed them and absolutely, day-in and day-out, depended on them. I am making zero recommendations here, just suggesting that you not worry too much about it. Pick one and go with it.

To extend the capabilities of the various trolling motors, it may be necessary to compensate. It's a simple deal, really. Drill two holes, thread for 1/4" pipe, screw in two plastic elbows, run a foot or so of soft walled tygon around the can, fill it full of oil and hit the water. (Wiring is the same either way. It ain't rocket science. Buy some bulkhead connectors and deal with it).

Conversely, if you've got the drawings for one of Kittredge's units, chuck it up in the lathe, cut to spec, add paint, prop and sea water, in that order.

Best Regards,
Vance