Join Date: Mar 2007
Location: New England
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THru-Hull Conversion Large to Small
So my 1979 Pearson 10M has flush mount cockpit scupper drains on the underside of the hull. They were mounted in with silicone and this year I decided to replace them. They weren't leaking, so the big question is, why screw with it? Well I did and opened up a can of worms.
The old thru-hulls have a angled flange (45 deg) with max diameter of 2.5 inches tapering a ^ 1.75 inches. The new thru-hull has a max diameter of ~3.5 inches, 45 deg angle and the inner diameter at ~ 2.0 inches and small step with a groove for sealant before it meets the threads. the old thru-hull has no step with groove before the threads.
Considering the following options:
- Widen the hole in the hull to accomodate the wider flange
- Machine the new thru-hull to match the dimensions of the old thru-hull. I have a machine shop looking into.
- Forget the flush mount and fill the beveled gap with thickened epoxy and use a regular thru-hull.
I am leaning towards #3 as it minimizes work and cost and reduces the area of seal.
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