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Hi Scott. I'm not an expert on the K boats but putting the "O" rings on the
shaft rather than inside the sleeve has an advantage. First off it's much easier
to make the groove on a shaft. The groove needs to be very smooth and as the
mechanism ages it will be easier to clean the groove and inspect it for wear. If
there are scratches or imperfections from the machining process in the groove it
can lead to "weeping" of water past the "O" ring when the pressure differential
is low like at or near the surface.
As for the sleeve, it's surface needs to be very smooth also. The area
where the "O" ring contacts needs to be very smooth. Think of the shaft on a
hydraulic cylinder.....Very smooth.
Whether the groove is inside or outside, a rotating shaft application needs
to be smooth so it doesn't wear out the "O" ring.
If the groove is carved into the shaft then the total diameter is reduced
at that point. If it's critical that the shaft be a certain size then it
will need to be increased in size to compensate for the groove.
Again, not being a K boat builder I don't know which penetration you're
referring to but here's a couple of thoughts. The shafts which rotate the side
motors don't spin very quickly or even make full rotations which tells me the
"O" rings won't receive a lot of wear. On the other hand the shaft penetration
for a motor inside the sub spins rapidly and will wear more quickly. In either
case though, the "O" ring isn't the "bearing" and if the shaft has any clearance
at all ( gotta be a little, right ? ) then the "O" ring will be compressed more
on one side than the other. A sealed roller or thrust bearing would be required
on both sides of the penetration so the shaft remains in the middle of the
sleeve and takes the lateral force on the shaft rather than the "O" ring being
used as a bearing. In the case of an inside motor this would be critically
important as the forces of the motor and propeller would wear out an "O" ring
quickly.
There's a company called "Parker" that has a good web site for all things
related to "O" rings and their information book can be down loaded. It
explains all the different types of material used for "O" rings and how each
material is best suited for a particular application. The book also has
information and diagrams on many different types of grooves ( they call them
"glands" ) and there's charts with exact dimensions for the grooves ( glands )
and many different types as it relates to a rotating shaft, extending shaft,
etc.
As to your question about "hardware store" "O" rings.....sorry, that ain't
gonna work. These "O" rings aren't made for serious applications or exposure to
the rigors of a submarine application. Get the info from Parker ( it's free )
and make your choice with that info. You don't have to buy the "O" rings from
them. In fact....you can't ! They only sell through distributors. You can
get "O" rings from McMasterCarr very cheaply. The "O" rings I bought through
Parker for my hatch were $140 for two and a big hassle getting through a
local dealer.
The same "O" rings from McMasterCarr are $16 each and easy to get.
Frank D.
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