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Dean,
It makes no matter if your keeping 200 PSI in or 200 PSI out. Your
seals still have to be able to stand up to a 200 PSI pressure differential so
why pressurized the pod? Why not just build the pod a bit heavier to take
the compression, and don't bother with putting pressure in it. Carbon
against ceramic seals are best if your going to be operating in the 200 PSI
range.
For most applications with small horsepower thrusters, the motors ball
bearings can handle the thrust load. But for 12 Hp you might want to dig
deeper. Determine what bearing is now on the thrust end of the motor shaft
and find it's thrust rating at the RPMs your operating at. It may be
high enough since you have almost no side loading on a prop shaft.
There should be bearing numbers on each bearing. If not, measure ID,
OD and thickness, count the number of balls in it and contact a bearing
supplier. They should be able to help you with it's load ratings. The load
is derated as the RPMs go up. On the other side, a bearing can handle a
very heavy load for a shorter time. You won't need it to operate for
20,000 hours. A few hundred hours of operations is more then most Psub
thrusters will see in their life time.
From there it's simply a matter of comparing the pounds of thrust you'll
get from 12HP spinning the prop your using to the bearings thrust rating.
Dan H.
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