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Catalina/Capri 25/250 Sailor's Forums

General Sailing Forum

Blisters -- Help, please!

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deastburn
Captain

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USA
334 Posts

Initially Posted - 01/18/2004 : 00:56:53

I am looking for information on blisters. Not for my C25, but for its possible successor. A boat I am interested in has lots of four-inch blisters (osmosis). I have never had such a problem with my C25 and hence have no experience in repairing thems.

How much of a job is it to repair each blister? What are the pitfalls of a boat, however nice, that already has lots of blisters. The boat has been living somewhere in Texas. If I buy it, it will live in the southwest coast of Florida. It is a 1985 30' Nimble.

Dave on "Wood Duck" (#2616 - SR, FK)

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Gary B.
Admiral

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USA
969 Posts

Response Posted - 01/18/2004 : 01:16:59

Dave: 4" blisters? Whoa-ba-do-bah! Those are honkers! It is no big deal to fix the dime/quarter sized ones by grinding them out, letting them dry, then filling in with thickened epoxy. But I would suspect that boogers this size might well involve structural problems in that they may be deep enough to have "infected" deep layers of glass. Have you had a survey by a reputable surveyor? I would.......then again, I would probably walk very quickly AWAY from this boat!

I'll bet that a moisture meter would show LOTS of water in this particular hull....My guess (and it's just that, although I have SOME boatyard experience) is that this puppy needs to have the hull peeled and reglassed and gelcoated. I suppose if you could get the boat cheaply enough to add that very significant cost, and had the time for the boat to dry properly (it would take months, I suspect, even under a heated, controlled environment). it MIGHT be worth considering....

Good luck,

Gary B.
Vice Commodore

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Mark Loyacano
Navigator

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USA
247 Posts

Response Posted - 01/18/2004 : 01:20:46

An experienced surveyor, knowledgeable about osmosis will identify the kind(s) of blistering you see. Gel coat blisters are common and not so difficult to treat. If the boat you are considering used poorly saturated chopped mat under the exterior gel coat and the woven roving another blistering will occur. If the glass woven material was contaminated before resin was applied there will be yet another sort of blister to consider. Different causes require different kinds of repairs. Even the use of moisture meters can be deceptive. Sometimes resins don't fully cure, they remain as a thick gel and show up later as moisture ... it is nearly impossible to fix.

It isn't all bad news though. There is a saying, no boat ever sank because of blisters.

Recently I inspected a severely blistered boat that showed large areas of white "dry" chopped mat beneath the dried blister spots. That bottom was most likely the result of resin that "kicked" before the matting could be saturated. Planners can peel through the defective layers and new glass be applied. It is very expensive to do this and the whole hull is weakened unless it is done right.
A competent survey and accurate estimates by a reputable boat yard will help you avoid ugly surprises later on.

Edited by - on

Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 01/18/2004 : 02:44:42

Dave,

I've watched discussions of hull blisters bring out lots of strong conflicting opinions. Here's mine.

I've seen and repaired hull blisters as wide as 6" and as deep as 50% to 60% hull thickness. When walking through haulout yards here around Port Canaveral, Florida it's not uncommon to see hulls that look like huge spotted leopards while under going blister repair.

My approach is to grind a shallow saucer shaped depression at each blister until all signs of oozing, resin starved, or delaminated fiberglass have been removed. No matter how wide and deep. If the grinding didn't need to go deeper than the thin layer of CSM (Chopped Strand Mat) between the gelcoat and outer most lamination of roving, then I fair that spot with thickened epoxy putty.

If woven fiberglass was removed, then woven fiberglass and epoxy resin goes back in, with the patch tapered 10:1 to 12:1 into the surrounding good original laminate. I prefer to patch with fiberglass cloth rather than roving, because I believe it results in a better fiber to resin ratio. I deliberately cut the fill patches slightly oversize so that the ragged cut edges end up proud of the final contour, and are not part of the finished repair.

After the repair cures enough to sand, I use a 4-5" right angle disk grinder or a 7" disk sander to rough fair the patch. In the case of deep or oddly shaped repairs, these steps may need to be repeated a couple of times, as it can become hard to eyeball how much depth and what shape remains to be filled near the center of the patch without first removing the rough excess around the edges, and then checking with a batten.

Once the patch is built up and rough faired to near the original hull surface, I finish fairing with thickened epoxy.

Once all blister and other needed laminate repairs are complete, it's time to final fair and apply barrier coat.

If everyone walked away from blistered boats, the landfills would be overflowing with them, and there'd be a very few expensive unblemished used boats on the market to choose from.

The blistered boats to walk away from are the ones that would look like swiss cheese by the time they were ground down to any remaining good laminate.

But, that's just my opinion!

-- Leon Sisson

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osmepneo
Past Commodore

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USA
1420 Posts

Response Posted - 01/18/2004 : 06:51:08

After I first hauled <i>osmepneo</i> and power washed the slime, I discovered lots of small blisters 1/4" to 1/2" in diameter. The fix is easy, really, and mine were strickly in the gel coat, and were along the water line.

However, "lots of 4" blisters" is another story. I would want the marine survey, with specific instructions to look at the blisters and a competent marine yard's estimate of cost to repair, even if you plan to do the work yourself.

Edited by - on

OJ
Master Marine Consultant

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USA
4382 Posts

Response Posted - 01/18/2004 : 14:34:02

Dave, the best $3 I ever spent was for this manual:

<u>Gelocat Blisters: Diagnosis, Repair and Prevention </u> (product #002-650) by Gougeon Bothers.

http://www.westsystem.com/

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deastburn
Captain

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USA
334 Posts

Response Posted - 01/21/2004 : 22:42:04

Thanks all for your help. One of the advantages of Northeast and great lakes boats is that they spend more time on the hard than southern boats, hecne tend to have fewer blistering problems. The Nimble 30 I was interested in has major blistering problems, and it seems best to me to walk away from it. If the hull has been allowed to deteriorate that badly, it does not speak well for the rest of the boat--engine servicing, for example. And there are lots of nice boats out there that don't have blisters.

Once again, this site is a fund of useful knowledge, information and advice. Thanks to all who responded.

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