Thus far in the project I have used silicone to bed all the hardware. I prefer silicone to polysulfide (Thiokol and BoatLife Life Caulk) and polyurethane (3M 5200) because the latter two tend to harden in the tube rather quickly. Unless I do a good deal of work in a two or three day period I waste much of these expensive compounds. In addition, the polyurethane is very runny and messy and rather more aggressive as a glue than I like for bedding hardware that may need to be changed or moved in the future. But silicone is far from perfect. It can become separated from bolt shafts and even from the joint between hardware and the deck. I generally assume that about 2 in 10 bedding jobs carried out with silicone will result in leaks that require a do-over.
This is why I have recently been won over by the arguments presented by those who use butyl rubber (see
http://forums.sbo.sailboatowners.com/showpost.php?p=705340&postcount=1). I employed the butyl to seal one of my opening ports. These ports are the old style with a flange that is inserted from the inside of the boat. Then a finishing ring is through bolted to the outside with bedding all round the flange.
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| The Port Opening in the Cabin Wall |
The flange is first wrapped with the butyl. Then it is inserted in the port opening in the side of the cabin. A segment of butyl tape is rolled into a thin strand which is wedged into any gaps between the hull and the flange from the outside. A small string of butyl is also wrapped around each bolt where it exits the cabin wall in a hole that has been chamfered. Finally the finishing ring is tightened in place over the butyl and any excess is pulled away.
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| Butyl Tape Wrapped Round the Port Flange |
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| The Chamfer Bit and Resulting Chamfers |
Hi Jim,
ReplyDeleteWas just thinking about Butyl tape to bed the large portlites at the aft end of the cabin, think I'll try it.
I have always used 420 or sika (doesn't seem to yellow) but it is messy.
Did you put butyl tape behind the outside flange on the ports, or just a bead around the inside?
Rod Munro,
Leading Edge
My portlites have rubber gaskets that go round the inside flange (you can see them in the pictures above). I put the bead of butyl along the inside edge of this gasket so that it would fill the small gap between the flange and the fiberglas.
ReplyDeleteThere is a brass ring that goes round the outside of the portlite (I did not show that in the pictures above I see)but it is meant just to dress the assembly up. I sealed it only round the machine screws where the nuts were applied after first camfering the fiberglass at each screw hole. So there is no attempt to seal the portlite from the outside.
I know that there are many other portlite styles. Some are sealed from the outside. But all of them should be able to make use of butyl rubber to provide an effective seal.