[PSUBS-MAILIST] Peddling to pump oil

["Dan H." <machine@epix.net>]

Good day Stan,

The last lines of your last posting on this site inspired me to post to
you.  I too am building a sub, although not designing from scratch,  for
almost the same reasons.  I like to create.  The more off the wall the
better.  I also find much of the satisfaction in a project like this is
in the learning and doing the research as I go.  It's not that I'm
brilliant but I like to dig for knowledge.

Anyway,  About your hydraulic Idea...........  I don't know if it's
worth it to go through all that trouble just to save having to deal with
one rotary through hull.  A seal for a rotating shaft that is good for
around 400 feet of depth is only in the $35 range.  All the hydraulics
will cost you a bundle.  Even more important, keep in mind all the
things that can go wrong with this more elaborate system that you
wouldn't have to deal with using one stainless steel shaft going from
your peddle arrangement to a prop blade.

I don't remember what depth you were talking about for this sub you are
designing but most hydraulic motors are sealed to keep oil in not water
out.  They usually have a case drain that takes any oil that leaks out
of the pressure circuit and delivers it back to the tank or low pressure
line.  The actual shaft seal isn't capable of holding total hydraulic
pressure.  I think you might find that you would be feeding sea water
into your hydraulic system through the shaft seal of any standard motor.

Another thing to consider is that to overcome internal leakage in the
pump, and somewhat in the motor also, most pumps aren't very efficient
when only turning at a slow RPM.   For this reason you would probably
have to use a speed up drive from your peddles to the pump.  You can
size the motor to do the reduction back to peddle speed for what ever
prop size you wanted to drive.   Each time your install more than a
shaft you loosing efficiency.  Unless you have all that mussel power to
throw away, not to mention extra oxygen consumption, I'd go with a $25
shaft and a $35 seal.

Dan H.   In Pa.