The problem with the silicone sealant is that it is meant to used as a
compression gasket material. The port light plastic tends to pull away from
the complex curves of the fiberglass surface since the materials expand and
contract at different rates. The plastic fails to compress the silicone
over time and the seal fails. The silicone material may last 50 years but,
in my experience, the seal fails in 3 to 4 years.
An alternative sealant suggested by Rummy for the hull joint but may work
fine here is as follows (thank you Graham):
For those who want more information on the sealant Rummy used for his deck
hull join now called Master Seal NP-1 (formerly Sonolastic NP 1) the spec
sheet is available here:
http://assets.master-builders-solutions.basf.com/Shared%20Documents/EB%20Con
struction%20Chemcials%20-%20US/Construction%20Systems/Data%20Guides/MasterSe
al/basf-masterseal-np-1-tds.pdf . (Note: The link is still valid on
1-10-19, copy attached)
The sealant seems to have all of the properties that would be advisable for
such an application such as high flexibility, can be immersed in water,
tenacious, sticks to anything and is available in a range of colours such as
off white. It appears to be available at Home Depot and is much cheaper than
the traditional marine sealants.
It is not clear that Beckson Marine would recommend it but it probably
wouldn't hurt the plastic.
Mike
s/v Wind Lass ('91)
Nissequogue River, NY
basf-masterseal-np-1-tds.pdf
