I would not hesitate to use the presence of blisters as a bargaining
tool if I was buying a boat but also would not let their presence keep
me from buying.

wrote:
I think that if you buy a boat, you directly ask the surveyor his
opinion on whether or not the blisters are a structural issue.


Definitely. And part of the out-of-water inspection must include opening
a few blisters, if present.


I have owned two boats with blisters. The first I repaired by drying
for 3 months and then grinding them out and filling with epoxy and then
several epoxy barrier coats (I know, not the same as a gelcoat peel)
and when it looked beautiful, it went back in the water and all my work
was hidden. A total waste of time as none of the blisters was into the
lam. The inside of the boat showed no problems at all.

If blister get all the way to the inside, you'd definitely have a problem!

A fellow was repairing a blistered boat near us, his had blisters the
size of softballs. I showed him how far into the cloth they were (when
you grind them out the cloth looks smooth), IMHO it was a serious
structural issue. My private opinion was that the boat was trashed, but
it's difficult to say that politely to a friend. He "repaired" it by
putting into each blister a little cut-out circle of auto body grade
cloth (maybe 8oz), two or at most three layers... to replace a couple
inches of matt & roving! Then putty to smooth it all over.


My current boat has some blisters and my strategy is to repair any that
look bad and ignore the others. I had a surveyor look over the boat
(not a real survey) for insurance purposes recently and he stated "No
obvious blisters" even though I had seen them .

If they're not up to golf ball size, then they're not all that obvious.
I've seen boats that had what looked like little teeny bubbles in the
gelcoat, smaller than your pinky tip... open them up and they start
looking like the Grand Canyon. Others where the bubbles really were
teeny little bubbles in the gelcoat, not what I'd call blisters at all.


... I think that if a boat
is over 20 yrs old and the blisters have not becom a structural prob,
they arent likely to ever be.


Depends... what about a boat moving to warm water. If it already has
small blisters in New England and you move to Florida, I guarantee those
blisters are going to become a major problem. Warm water seems to
magnify & accelerate blisters.

The only way to *cure* blisters is to put the boat in a body-bag and
pump in hot dry air to remove all moisture from the laminate. Just
letting it "dry" in open air in a climate averaging 50% humidity ain't
gonna do squat. OTOH plenty of people get lucky doing it that way...
shows that the blisters weren't that bad to start.

Fresh Breezes- Doug King

I find that David Pasco has the most comprehensive knowledge of
blistering alongh with experimental data. Most other pundits on this
topic quote heresay. Pasco says that in 95% of the cases, the blisters
are of no structural concern. He says Blisters rarely penetrate the
laminate unless the laminate is very poor. He has a picture of a boat
where the structure was not normal laminate but short lengthh fibers
over foam, sorta like applied with a chopper gun resulting in very low
strength.
I did find another site that says that blisters sometimes penetrtae the
laminate but they do not define what they mean as well as Pascoe does,
One reference was to a Cal that had serious lamination problems but the
owner stated he thought it was a layup problem and not the direct
result of blisters.
Pascoe has little good to say about blister repairs and from the way I
read, it seems that you are better off doing nothing unless something
indicates hull failure. Other than the one pic Pascoe has, I saw no
documented evidence of hull failures although there were apocryphal
statements about keel/hull failures but again, no evidence.
I therefore stand by my statements about not worrying too much about
blisters unless you have real evidence of a problem.

http://www.hotvac.com/process/default.aspx

"HotVac treats boats by…

* The thorough removal of absorbed water from affected hulls.
* The removal of acids, glycols and other organic compounds that
cause corrosion, glass to resin bond weakening, delamination and
blistering. "

XXXXXXXXXXXXXXXXXXXXXXXXXXXX

http://www.boats.com/content/default...tentid=1899how to
tips
Fiberglass Blisters
Effective prevention and treatment

"The hull must then be dried, to get the saturation of the laminate
below 50 percent, which can take considerable time, as reflected by
the following table:

Temperature 50% Relative Humidity 25% Relative Humidity
100 F l6 days 9 days
83 F 32 days 18 days
65 F 64 days 36 days
47 F 128 days 72 days"

I dont have the reference handy but the amount of water a hull can
absorb is quite significant, and yet not have any ill effects although
not universal. I guess some of the issue is where the boat is
seasonally hauled out and whether it is fresh or salt water...

Blister Cause / Repair Links

http://www.zahnisers.com/repair/blister/blister1.htm
http://www.yachtsurvey.com/blisters.htm
http://www.marinesurvey.com/yacht/BlisterRepairFail.htm
http://www.hotvac.com/
http://www.osmosisinfo.com/
http://www.daviscoltd.com/nams/Docum...er_Report.html

With soft ball size blisters you'd have to look at them anyway so go
ahead and cut them open. If they are not into the laminate, I'd say no
structural problem.
One web site discusses actual measurements on blistered LAMINATE and
found that the tensile strength was hardly affected but they noted that
flexure might be a problem causing the hull to "oil can" if the
LAMINATE was blistered (a rare condition).
One potential "solution" I have never heard anything about for people
who are concerned about possible structural problems but who
cannot/will not peel the gel and skin coat is to add a layer of
epoxyand glass INSIDE the boat. For a small lower value boat like mine
(28' worth maybe $15000), this might alleviate some structural worries
without spending a huge fraction of the boats worth on a gelcoat peel
that probably will not solve the problem.
Even with a worst case scenario, for a normally built laminate, I do
not think anyone can point to any accident caused by structural failure
due to osmotic blistering. Just in the interest of gathering data, I
invite anybody who has real knowledge of a real structural failure due
to osmotic blistering in a conventional laminate to post such info.
I tend to be a skeptic about blistering woes partially because of a
Practical Sailor article years ago where they decried the longetivity
of fiberglass boats as depressing the market for new boats. At the
same time, they hailed the blistering problem as a possible saviour of
the boatbuilding industry. In other words, there are many people with
a vested interest in creating problems where they may not exist.
My experience with boat yards has never been good although this may be
a product of living in a place with no good ones. I have found that
generally I will do a better job than they will and that they can be
expected to take short cuts. In blister repair, all short cuts will
cause failure of the repair.
Pascoe noted that even some of the best known highest quality builders
had severe blister problems so it isnt confined to low cost or low
quality boats.
In summation, I would not reject a boat with blisters but I would get a
surveyors opinion and use the blisters to bargain.

Let us consider relative risks of boating things. We all know of
accidents caused by keels falling off external keeled sailboats, if
not, google Mike Plant. Yet, I have never heard of an accident caused
by blisters. This means that external keels are far far more dangerous
than even the worst case of blisters. So, should I reject all boats
with external keels? Actually, I would.
I have never heard of anybody being adversley affected by blisters
while they were on the water. Considering that many people here who
would not have a boat with blisters actually sail even when they are
near thunder storms, you have to wonder about their perception of
relative risk. The risk of lightning strike even without thunderstorms
is probably thousnads of times higfher than being affected by blisters.
I have heard of prop shaft breakage sinking boats but have never keard
of problems from blisters while on the water. Considering the relative
risk of blisters causing problems, I have to conclude the risk is
relatively non-existant.

I actually consider all external keels to be more of a hazard than most
cases of blisters. In most cases, it is imposible to detect metal
fatigue in the keel bolts and even going aground softly can cause
failure in them. I think statistics will bear me out on this relative
comparison.
Sailing through thunderstorms intentionally is seriously foolish, even
being on the water when one is near is foolish compared to sailing on a
boat with blisters. Statistics easily show that the number of boating
deaths from lightning NOT originating from thinderstorms is very high
compared to those from blisters. I live in Florida so am very
cognizant of the risk of lightning. Last year I actually calculated
the risk of getting hit by lightning (a long discussion here) assuming
some reasonable conditions and was amazed at how high it was. A
susbesquent examination of insurance claims bore out my calculation.
Compared to lightning, the risk of blisters is nonexistent.
I can think of no reason why boats with serious blisters would get any
less use than others except in extreme circumstances, yet these extreme
circumstances cause vety few of the accident stats.