Blisters on the hull...

[Mike H.]

Hello to all...   I've got a dumb question.  For the two years (almost) I've owned my CP16/2 I've kept it on a trailer.  My family has a camp and we just had a new permanent dock built & now I have a place to leave my boat in the water all summer if I want to.   My question is how long does it take for blisters to form on a hull? Are blisters inevitable if left in?   My boat has bottom paint on it that I'm sure is quite old but the coverage still seems good(?).  There is a boat launch about 100' down the road from our camp so I can drop it in and take it out as I please w/no problem.  I thought maybe keep it in only when I'm there & park it when I'm gone, or leave it in for a week or two at at time.  Just curious, my boat is in pretty good shape & I'd hate to blister the hull.  

I hope everyone had a great winter and will have a better spring/summer...  I look forward to your responses.

Thanks,
Mike

[curtisv]

Mike,

Your risk of blistering increases with the length of time you boat is in the water, higher water temperature, fresh water, and the type of gelcoat used.  You didn't say where you'd be putting the boat in the water or the year of the CP16.

In any case, blistering varies from highly likely in bathtub warm fresh water in a southern state where the sailing season approaches all year long to very unlikely in Maine salt water where you have to haul out at least during the months when the water may freeze.

Rumor has it that before the 1970s gelcoat and fiberglass were more resistant to blistering, after that it became a problem due to changing process in response to higher material prices, and then got better again in the late 80s or 90s when the type of resin changed.  Maybe someone on this list has the details.  A number of books on fiberglass boat repair cover the topic.

If you are at high risk, you can put an expoxy barrier coat on.  Bottom paint only keeps the critters from growing on your hull when it sits in the water.  It doesn't help much if at all with blistering.

As an example, a couple nearby owned a Tartan 34 (I think, not sure) that was about 15 years old and never blistered in that time.  The original owner had her in fresh water.  This couple sailed her off Cape Cod in cold salt water.  When they took off for the Caribbean one fall they returned the next spring with a huge blister job on their hands.  The warm water had blistered the hull quite badly.

Water temperature matters a lot.  Its more or a risk than a certainty even in warm water.  Its a very low risk in cold water.

So ... where do you sail?

Curtis

[Craig Weis]

The Com-Pac woven cloth impregnated with resign and hand rolled into the mold leaves little doubt that the hull below water will ever blister. To blister water must penetrate the wet layer and lodge between the glass and the substrate, such as a wood core. Com-Pacs have no wood core, and in fact the resign was embellished with micro~balloons. So no core means no water. If there is water then there is a hole in the hull clean through but never 'between layers that don't exist'.
All the wood inside might rot and anywhere where water and wood meet, like the tabernacle reinforcing wood glassed into the deck or under the winch and cleats as hard points but then again the resign surface is cracked, and a crack creates a layer and that can blister by somewhere letting water in. So enjoy the dock and let her float. Glass will absorb a little water and the boat becomes a little heavier but not any measurable amounts

skip.

[beshman2]

Not to contradict anyone here, but I spent the winter of 2008-2009 grinding out blisters on the keel of my 1980 CP16 and refilling them with layers of glass and RAKA epoxy.  The bottom was covered with a rough coat of bottom paint and the boat had been sitting on the trailer for several years.  I stripped the bottom paint and was amazed at the number of blisters.  I put an epoxy barrier coat on the entire bottom below the water line and repainted the bottom.  It looks pretty rough up close, but it is fine from 20 feet and can't be seen under the water anyway.  Not sure where the original blisters came from, but they were there.

[brackish]

To blister water must penetrate the wet layer and lodge between the glass and the substrate, such as a wood core.


Not accurate Skip, the vast majority of production sailboats do not have any core in the hull, just in the top sides, particularly those areas that are walked upon.  The hulls are generally solid glass, and they certainly will blister.  Blisters occur when water penetrates the gel coat by osmotic action and collects in the glass.  I had two solid hull Columbia's, both of them got blisters.

The modern resins are much better at preventing such action, epoxy barrier coats offer even more protection.  There is one camp that says it does not matter.  I sailed my last Columbia for over ten years with blisters, did not seem to get appreciably worse of affect the structure or performance in any way.  Every year I said I was going to fix them......every year I procrastinated till next year.  Think they may still be there.

[curtisv]

Mike,

There have been lots of reports of Compacs blistering.  The majority of Compacs don't blister and as boats go Compac hulls seem to be less prone to blistering on average.  There were a few technical summaries of the cause of blistering on the yahoo group site a number of years back.

There is good coverage of this topic in some of Don Casey's books.  I have a few listed on my web site at http://www.faster-light.net/remote-access/book-reviews.html#fixit.  The book "Sailboat Hull & Deck Repair", by Don Casey has good coverage of this topic and very practical advice on preventing and treating hull blisters.

I've said about all I remember off the top of my head about this.  These books are worth owning so this would be a good excuse to get a copy.

Curtis

[Craig Weis]

I agree. A crack is needed to blister. And yes glass will absorb water. If sealed...you'll not blister. And if blistered and not leaking the blisters don't matter unless your racing. Grind'em down, fill'em, and paint'em.

What I don't like are those tiny tiny little 'spider cracks' in unyielding fiberglass after I 'stupidly' bolted someting down way too tight, cracking the glass. That lets water in and water freezes up here 5 months a year. Or so it seams. I have been using that liquid crack filler and when dry a goodly amount of rubbing compound, elbow grease and Mother's wax. There there but I can't see them. Of course the wife says I'm nearly blind anyway. LOL

Sun 17 Cat writes "It has always been my understanding that fiberglass will absorb water (a crack is not needed). Any surveyor will check the hull to see what the moisture content is and that way you can know how much has been absorbed into the hull. If you don't keep your boat in the water this should never be a problem." That's true.

skip.

[sun17cat]

It has always been my understanding that fiberglass will absorb water (a crack is not needed). Any surveyor will check the hull to see what the moisture content is and that way you can know how much has been absorbed into the hull. If you don't keep your boat in the water this should never be a problem. If you do then a good idea is to have an epoxy barrier coat applied and the problem should never occur. If you buy a new ComPac and have it bottom painted at the factory you will automatically get two coats of epoxy before the bottom paint.

Jim

[curtisv]

No crack is needed.  Some gelcoats are more porous than others.  Fiberglass resin absorbs water unless it is epoxy.  Few boats are made with epoxy resin today.  Next best is vinylester gelcoat I think.  Don't have Don's book handy at the moment.

Curtis

[jpfx]

the armorpoxy paint on my hull had blistered significantly in 6 weeks last season. I don't know yet how deep it goes... I popped a few big ones initially (full of acidic water) and it could be contamination between old layers (of paint). I think poor preparation may have been at the root of the problem.
I would expect a similar reaction within a couple of months with a better prepped hull, to the extent that I plan on keeping it on the trailer.

[Craig Weis]

Like any coating job, preperation is 100% of a 'Good Stick'.
skip.

[mrb]

Just for the record here is another cp-16 that has had blisters.  My boat did come out of Florida waters.  I would recommend a epoxy barrier coat for peace of mind.

Melvin

[douglt]

Am presently grinding out about 1000 blisters on a 1976 Compac 16.  Boat has spent it life in Florida fresh water.
All the research I have done indicates that the cause of the blisters is osmosis through the gelcoat.   They are a pain to repair.
Boat is going back into a fresh water docking, so we will see what happens in a year or so.
Doug

[newt]

I have ground my fair share of blisters, but usually from Catalinas- not from our little Compacs! I think a few things need to absoulutely, positively be done for a good blister repair.
1. The hull needs to be bone dry.
2. the blisters need to be completely ground out.
3. The hull needs to be sealed from future water invasion. Many believe that the sealing should be inside and out.
4. And you need to have a great deal of luck.
Living in a desert, it is not hard for me to get #1 done. #2 you just need alot of patience and tolerance of hard work. #3 is skilled work, but usually can be done DIY.
Good Luck, and I hope this is a learning experience for you. It was for me