Join Date: Sep 2008
Location: Victoria B.C. Canada
Thanked 109 Times in 100 Posts
Rep Power: 10
Butyl does need to be in compression to be effective.
A good idea would be to form a glass riser where the chainplate emerges through the deck - it will avoid water pooling around the chainplate. You can put a plate on if you wish. The link below explains - scroll down a bit.
Maintenance Log for Syzygy
Living aboard in Victoria Harbour