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Old 16-09-2004, 10:00   #1
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Hull Blistering

Hello all,

I would like to ask some questions regarding Blistering.
Is this a problem that occurs on ALL boats over time or is there more of a problem with older boats.
What is the best way to repair blistering and what are the potential problems in purchasing a boat that may have Blisters.
I had someone tell me that the Quarter size blisters on the bottom of his boat that he was selling were deemed "Not a problem" by the yard and that no treatment or fix was being advised at that time.
How could this be? From what I gather blistering and it's affects are considered to be detrimental to the hull.

Anyone mind elaborating on this issue?

Fixes, causes, problems or complete avoidance?????


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Old 16-09-2004, 10:24   #2
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The Pox

Best paper I've seen on this subject
Zahnisers is a very well respected yard in the Chesapeake.

Rick I
Toronto in summer, Bahamas in winter.
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Old 16-09-2004, 19:15   #3
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A few blisters now are a good sign of more blisters later. Some manufacturers have had zero blisters. Do as much research as you can. I would suggest you do not buy a boat that has had or has any blisters unless you like spending $$$. Ocean Navigator had a two part article on blister repairs earlier this year. Take a look at and search for blisters. Look under articles. After you have read heeps about the subject lets talk some more.
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Old 16-09-2004, 19:45   #4
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NO, not all boats had blister problems.

It had to do with the lay-up and the gel coat and if them moons and stars were aligned and all that.

Some of the "cheaper" boats ended up with more blisters than the expensive ones....Surprice, surprice.

Morgans for instance, in many cases are infected.

It also have to do with fresh water / salt water...Cold water / warm water, etc.
As well as currnent or flow along the hull when the vessel is sitting at the dock.

Many variables, but with a thin hull, ya have less margin to repair them blisters..With a thick hull ya can scrape the cancer out, fill with epoxy and go sailing.

With a thin hull, the blisters can go almost through and weaken the structure..
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Old 20-09-2004, 15:58   #5
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Interesting side note, prior to 1982, blisters were practically unheard of. In 1982, two things happened at once, an oil shortage, and a new regulation regarding fire safety in the manufacture of gel coat ... consequently, the formula for gel coat was changed. It was thought to be as water impermeable as the old formula, but was not. It took several years for the problem to appear .. and the formula to be changed once again. Boats built between 1982 & 1985 have the most problems. My boat is a 1982, and I was thrilled to find a receipt in it from a yard that had replaced the rudder stock bushings and had done a complete strip of the old gel coat (below the water line) and done an epoxy bottom job on her.

L S/V Eva Luna
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Old 20-09-2004, 19:35   #6
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We did a blister job on our boat when we bought it. It was a big job but WOW what a nice bottom she has now!! Our surveyor said that it was something that would need to be taken care of sometime down the road but was nothing to worry about at the time.
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Old 21-09-2004, 05:10   #7
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Just to touch on a couple points here. Blistering does not occur on all boats. There are several forms of blistering and it is important to understand which form a boat has.

The most common form of blistering occurred on US built boats constructed after 1972 and up through the mid to late 1980's as a result of the reformulation of polyester resins that occurred as the result of the oil crisises of the 1970's. This type of blistering can generally be treated by barrier coating the below the waterline hull and the bilges of the boat. This form of blistering usually produces comparatively large diameter blisters that will progress through the laminate if left unrepaired. Grinding should be minimized on this form of blisters since the heat can produce blisters deeper within the laminate. Peels and sandblasting are a better course of action followed by a lay-up of F.G. cloth and either epoxy or vinylester.

The second form of blistering tends to occur boats built before the 1970'e reformulation. It typically is the result of over accelerated resins and resin rich laminates. This form of blistering rarely crosses more than one laminate lay-up and can occur as localized patches. In the worst case, where the boat was laid up with over catalized resin or over accelerated resins the problems can move quickly deeper into other laminate layers. Early Columbias and Coronados are considered to frequently have this problem. Many Oriental boats were prone to this problem long after the US had come to realize the problems with using over accelerated resins and resin rich laminates.

A lot of later boats have simple gelcoat to laminate blisters. This occurs when the Gelcoat goes off or gets contaminated before the laminate gets applied. This is sometimes called a 'friday boat' syndrome meaning that it is assumed that the gelcoat was applied on a friday and the layup occured the next week. This is a pretty benign form of blistering that can be repaired by popping off loose sections of gelcoat with a sharp chissel, lightly sanding the laminate and filling with thickened epoxy. This form of blisters are generally, shallow, small in diameter and appear more densely on horizontal surfaces.

There was mention of fire proofing of fiberglass. That was not a code requirement nor an industry wide problem. Only very few manufacturers experimented with a fire resistant polyester resin, Valiant being the best known. It was not just the gelcoat that was fire-resistant resin. In many cases fire resistant resins were used throughout. This is a very serious form of blistering since it can effect the entire structure of the boat and there really is no good way to permanently fix this problem.

There was also mention that blisters were more of a problem with inexpensive boats. Strictly speaking that is not the case. Price seemed to be less of a determinant that the materials and construction methods chosen. Valiants for example were a very high priced boat for their day. Late 1970's era Hinckleys have been known to have very serious blistering problems.

Higher quality thinner hulls were less prone to blistering problems since greater care in the lay-up was required and resin rich layups were avoided. Cored hulls tend to be less prone to blister problems and are generally easier to repair if a problem occurs.

Otherwise, if you only have a few shallow blisters, open them up, clean the area well, allow to dry out and fill with thickened epoxy, check the boat regularly and then move on in life.


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