I've been hearing more and more boaters talk about using butyl tape
for sealing hardware bolts, boat windows and similar items on boats.
It it used only where two items are screwed or bolted together. It is
the soft, tacky stuff used by window installers. I've been using it
on my boat lately. It is very easy to apply and work with, compared
the usual 3 sealant types (silicone, polyurethanes, polysulfides), but
I am interested in what others think.

According to some internet research, some boaters have used it for
years, and after years under a fitting it remains pliable. According
to one manufacturer, it has these properties (quoting their website):

# Adhesive: Butyl rubber has excellent adhesion to most materials,
(But it is not an "adhesive" like 5200) such as: all of metal, wood,
glass, zinc, concrete, etc. (fiberglass is not quoted here.)
# Heat & Cold resistance: Because of heat-resistance and
cold-resistance, Butyl rubber can be used under any temperature
conditions.
# Excellent Dielectric insulation
# Anti-corrosion: Butyl rubber prevents surface corrosion from
moisture and steam.
# Easy application.
# Excellent resistance against UV rays.
I would add "conformability".

I found this at a competitor's site: "In recent years, all butyl tapes
have become taboo to our industry, and for good reason. Butyl tapes
are not an adhesive and should never be used to install a windshield
or any glass that is not mechanically fastened to the vehicle.". But
I use it only around bolts, to prevent water ingress.

The truth??

Jim