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Why are stuffiing tubes no good for subs?

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Why are stuffiing tubes no good for subs?

Postby flying jeep » Tue Feb 22, 2011 10:21 pm

I have a real newby question: Why are stuffing tubes no good for subs? My type IX sub has some really long tubes that are a really close tolerance with some heavy grease and have not leaked on the surface. Is the pressure a foot under water that much greater to push all that grease into the water tight compartment? If you've seen my other post, you'll see I'm up against a 20 year old re-engineer and rebuild on this great hull and I only want to do it once. I just received a sample copy of the Sub Committee Report and was suprised to see another modeler with a working design similar water tight compartment as mine. But he didn't show the drive shafts.

Thanks,
Jay
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Re: Why are stuffiing tubes no good for subs?

Postby Bob the Builder » Wed Feb 23, 2011 1:01 pm

Your water pressure increases dramatically even a few feet under the water (0.43 psi per foot of depth).

In normal operation, cruising your boat at periscope depth or just under, you'd probably be okay. Venture deeper, or (heaven forbid) bottom your boat in a deeper pond and you've got perhaps ten feet of water pressure pushing on the grease now. You'll flood your boat for sure.

The shaft seals available commercially are cheap and very effective. They also take up far less room than a long stuffing box while providing far less resistance to rotation.
Bob Martin,
RCSub homepage: http://www.rc-sub.com
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Re: Why are stuffiing tubes no good for subs?

Postby flying jeep » Wed Feb 23, 2011 8:54 pm

Okay, I'll buy that. I remember my scuba lessons on depth and pressure. It gets ugly fast.
Jay
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