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Old 12-10-2012, 21:40   #1
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Double bevel butyl?

Hi everyone. I am refitting a forward hatch. The Steel of the boat and the hatch don't quite fit up, so I'm making a 1x2 trim piece out of mahogany.

I'm planning to use Butyl rubber to seal it, I've bevelled the bottom edge, and I'm wondering if it would be advantagious to bevel the OTHER edge as well? It'll be screwed from the bottom up into the wood. THe wood sealed with epoxy (and varnish)

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Old 12-10-2012, 22:45   #2
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Join Date: Nov 2007
Location: boat is in WA
Boat: Skookum 53 ketch
Posts: 145
Re: Double bevel butyl?

Not sure if you are planning to bevel the butyl seal or the wood surface. In either case you will need some sort of dimensional control on the bevel to get a good seal all the way around. Comparing that to my port lights, the seal is flat and the bronze is beveled. Comparing that to my aft commercial hatch (have an ex-commercial fishing boat), the aluminum surfaces are flat and the seal is beveled (actually u-shaped in cross section).
You may want to check on the durometer of the seal material. If you check the McMaster Carr website, they sell all kinds of seal material. I kind of like 50 durameter silicone seal material because you can compress it quite a bit. That being said, I've been fabricating access hatches for my water and fuel tanks. I was looking for sheet material for the water tank, and settled on some FDA approved Buna N (nitrile) rubber. It has no odor. Its 70 durometer,1/8" thick, but the access hatch is bolted together so I can apply more pressure. I have noticed that some ofthe pre-fabricated fuel tank access plates use 70 durometer.
If you are talking about a hatch that you can open up (ie, clamps,dogs, etc,but no bolts), I think you want go pretty thick on the seal; maybe 1/4 - 1/2".
Another place to look on the internet that may have some good information would the manufacturer Parker Seal. The make all kinds of seals. From an engineering standpoint, you try to match up the dynamic compressive range of the seal (function of shape, compression loading, and material) with the mechanical constraints (material and surface finish, plus coefficient of thermal expansion) of the gland (the mating surfaces). I know how they work, but I don't have enough knowledge for my own projects to do more than copy what the commerical hatch manufacturers sell.
Hope this is of some value. Good luck.
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