I'm *so* sorry to hear your boat has blisters. When I read it, it was like
hearing that a member of the family was ill. I would be *so* upset if it were
my boat.
I have read that blisters appear in many forms. One form, and that may be
what you're seeing on your boat, is multiple blisters the size of pencil
erasers. From what I've read, you always want to be present when your boat
is hauled out (this is for bigger boats than the Potters), because they can
shrink quite rapidly after haul-out. I sounds like this is the case on your
boat. Unfortunately, just because they shrank down, it doesn't mean they're
gone.
I don't have a lot of references in my boat library on repairing blisters, -
just one - the Gougeon Bros/West System booklet _Gelcoat Blisters: Diagnosis,
Repair and Prevention. It's a comprehensive 45 pages on the causes (physical
and chemical) and detailed how-to instructions on repair and preventing future
re-occurances.
Whether you do the repairs yourself or hire a boatyard, I highly recommend
reading it. It's going to be an expensive or time consuming repair, and you
want to do it right the first time. Let's hope the first time is the last
time!
>From the limited knowlege I have, the long and short of it is that you're in
for a lot of work. In all probablity, the blisters are caused by water
permeating the exterior gelcoat and reacting with water soluble material
within the polyester resin, creating pockets of acidic fluid.
The damage usually starts at the interface between the gelcoat and the
laminate. If you catch it now, you can probably repair it before significant
damage is done to the laminate. The damage usually starts at the outer
surface and progresses inward uniformly. Since you describe damage over all
of the area below the water line, I'd guess that's how it happened on your
boat.
If you have isolated blisters (and what you describe doesn't sound like this),
it's possible to repair individual blisters. IN your case however, it sounds
like you might have to grind off the gelcoat down to the laminate, then clean
and dry the area, then apply a moisture barrier, then apply a good bottome
paint. You may have to repair some of the laminate itself. It's a big job.
For the other listserv members reading this post whose boats don't have
blisters: The booklet makes recommendations for preventing blisters. It
boils down to two things -- (1) Keep the interior dry and maintain the
moisture barrier (in this case getcoat). That means no water in the bilges
and maintaining proper ventilation inside, including under the berths etc.
and (2) maintain a continuous barrier coating (fix scratches ASAP), dry haul
for winter, be careful if you sand your bottom and apply anti-fouling paint.
As for as maintaining the moisture barrier, the booklet say that once you sand
and bottom paint it, you've got to maintain it. I wonder if your problems
stem from repeated sanding and re- bottom painting. Perhaps at some point,
you sanded enough of the gelcoat off to make it too thin. For boats that have
been sanded, it's important to be sure you re-apply a barrier coat (rebuild to
20 mils thickness) before you apply the next years bottom paint.
Again, I'm sorry to hear about the blisters. The West system booklet would
help you assess your situation and make a decision about how to proceed. The
book says that as many as 1/4 of all boats eventually develop blisters, but I
know that it's no consolation to know that you're not alone in fighting this.
Fair winds,
Judy B.
Judith Blumhorst, DC
HMS18/P19 Sail Captain, Potters Yachters
WWP-19 #266 "Red Wing"
SF Bay, CA