The seal should be between the outer hull and the part of the through-hull that contacts the outer part of the hull. A good bedding compound like 4200, sikalex or life caulk works well. I don’t seal the threads on the inside of the backing nut but that is your choice. My hull is solid glass, not cored so it doesn’t matter if water can get into the hole from the inside.
From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Marek Dziedzic via CnC-List Sent: Monday, April 13, 2015 9:01 AM To: cnc-list@cnc-list.com Subject: Stus-List sealing through-hull Hi, I have a question that may sound basic: One of my through-hulls (drain for the head’s sink) started to leak last spring. I solved the issue temporarily by tightening it – the valve (seacock) screws onto the threaded through-hull. This spring I want to solve this problem permanently. I just went to the boat and disassembled the seacock/through-hull. To my surprise, I found no seal between the seacock and the through-hull. There is a beefy backing plate and the PO (I don’t think it is factory) put some silicone on it. But there is nothing there that is designed specifically to seal that joint. Here is a link to a sketch of how this looks like (don’t lough at my drawing skills): https://www.dropbox.com/s/tgll2zglwvskdcr/throughhull.jpg?dl=0. The question is how do you correctly seal the joint between the through-hull and the seacock. Both are Marelon. The seal is required on the threads of the through-hull or between the backing plate and the valve body (the red arrows in the picture show the spots). An added difficulty is that the valve has a 90 degree elbow and it has to point up. So it is not necessarily possible to tighten the connection and to position the valve correctly. I am thinking of making a seal that would fit between the valve body and the backing plate. However, the correct installation calls for securing the valve body to the backing plate with screws, so the seal should be between the threads. Any suggestions would be welcomed. thanks Marek 1994, C270, s/v “Legato”
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