Questions on Blisters

[macowneril2015]

So I have dug through here and noted others have had a bunch of small blisters all over the hull of my when I pull out at the end of the season. I have noted they do not get worse and go away within a couple hours of being out of the water. I need to reapply bottom paint and was considering getting it sanded/ blasted and getting a barrier coat and bottom paint put on. My concern is when the boat is sanded that these legacy blisters will open up resulting in additional cost and work. Any guidance is appreciated as I can just get anti fouling reapplied and just enjoy the boat but I have wanted to try and get it done right.

[NiceAft]

I don't believe bottom paint is good protection against blisters. That's what the barrier coat is for.

I had my Mac at a slip for three seasons with only a barrier coat. because I only sailed in fresh water, I only had to deal with algae at the end of the season. I took care of that with Slimy Grimy powder. In twenty years I have never had blisters, and have never replaced the original barrier coat.

Blisters coming and going is new to me. Someone else may enlighten both of us.

[Be Free]

Ray is 100% right. Barrier coat prevents water from soaking into the bottom which is the usual cause of blisters. Bottom paint discourages the growth of marine organisms on the hull.

A blister that goes away that quickly is probably in or under the top layer of your bottom paint. A true hull blister takes a lot longer to shrink and usually requires sanding to remove completely.

[Russ]

Yep... barrier coat is what prevents osmosis or whatever it is that causes blisters. I may get flamed for this, but Roger used poor gelcoat and blisters happen. First year I pulled out and had tons of them. Still do. Some have popped. Mine aren't that bad and I haven't seen intrusion into the glass. But they are there.

In retrospect, I wish I did a barrier coat. Fresh water seems to be worse for blisters. Probably because it's not as dense.

I've got 'em. I ignore them. In 11 years they haven't gotten worse so I look the other way and can't see them once the boat is launched and floating.

Should I fix them? Probably. But they simply haven't been bad enough to drive me to do all that work.

[OverEasy]

Hi Macowneril2015!

I’m sorta more cautious than others….

If you have blisters like you describe they may ver well be actually into the fiberglass which can be a problem.
Covering them over may not be the best idea.

They may be draining “fast” because someone (or circumstance’s) have “popped” them at some point.
If I may suggest…. It’s always better to know facts and work within them than for wishful thinking.

When hauling out mark the shape and size of all the blisters you are able to see before they drain.
It might help to make a map reference to find them later on… I’ve used a tape measure in the photos from a common reference point like the stern
Observe the blisters…do they have pinhole drainage you can see?
Press on the blisters….are they stiff or gushy soft?
>>> stiff means they are gonna most likely be in the actual fiberglass and should be addressed
>>> gushy soft like partially filled baggy or balloon might mean it is only under a layer of paint … you may be lucky in that aspect

If I had osmotic blisters I would be inclined to deal with it sooner rather than later… the problem only gets worse and can affect hull integrity. We have relatively thinner hulls as trailer sailers than fixed keel boats. So not a lot of thickness to compromise. Exposing and blending and applying new fiberglass is the only relevant solution. Often they are shallow in the early stages so not too much of a task.
The void space an osmotic blister creates is generally befouled with crud and slime… nothing will stick to it so there isn’t an “injection” option that’s valid.

As far as repair costs it varies a lot and is dependent upon the actualities of the particular situation.
Dealing with known facts allows you to plan accordingly and responsibly. Good Boats like MacGregors tend to get passed down or sold to multiple owners so there is an integrity aspect to consider too. One wouldn’t want to potentially cause harm in the future if avoidable.

Now once actually fixed the application of two or more coats of barrier epoxy paint up to above your water line will generally ward off future osmotic blistering issues.

As whatever the problems may be that exist I’d want to know.
Getting the hull blasted is a good start… the photo map of the marked blistering gives you a good reference to check against once it’s cleaned.
If the blisters were only under the paint (barrier or ablative) then your well prepared for the new barrier paint coatings to be applied followed by your bottom treatment.
If the blisters are in the fiberglass then you’re at a good place to address them properly.

It’s ultimately your call on what you want to do.

Best Regards
Over Easy

[mars]

Hi Macowneril2015!

I'm dealing with the same problem right now. There were lot of blisters on some parts of the boat (I have 26S from 1992). I decided to send the boat and I just finished sending today. All of the blisters were caused by water entering between the gelcoat and the fiberglass (I use the boat at a lake, which means fresh water), and some of them, the biggest (about 5mm in diameter) smell like acid, which means osmosis. Lacily, only handful of them were like that, but they started to "eat" the fiberglass (about a half of mm deep). Most of them were smaller and were filled with water. But, all of them were between the gelcoat and fiberglass. So I decided to send the boat and put protective coat. I stripped about 20% of the gelcoat were the blisters were very dense. For the rest of the boat I only took out the antifouling and primer, the gelcoat was fine and there was no need to strip it. I'm planning to put three layers of protective coat and, after that, antifouling. Hopefully, I'll finish that in a few days, but we'll know if I were successful in October when I put the boat out of the water. I have to admit, It took a lot of work to do that and I'm very happy that a couple of friends helped me to do it. If it is of use to you I can send more details about the process and some pictures to compare with your problem.

Cheers!

[macowneril2015]

Hi Macowneril2015!

I'm dealing with the same problem right now. There were lot of blisters on some parts of the boat (I have 26S from 1992). I decided to send the boat and I just finished sending today. All of the blisters were caused by water entering between the gelcoat and the fiberglass (I use the boat at a lake, which means fresh water), and some of them, the biggest (about 5mm in diameter) smell like acid, which means osmosis. Lacily, only handful of them were like that, but they started to "eat" the fiberglass (about a half of mm deep). Most of them were smaller and were filled with water. But, all of them were between the gelcoat and fiberglass. So I decided to send the boat and put protective coat. I stripped about 20% of the gelcoat were the blisters were very dense. For the rest of the boat I only took out the antifouling and primer, the gelcoat was fine and there was no need to strip it. I'm planning to put three layers of protective coat and, after that, antifouling. Hopefully, I'll finish that in a few days, but we'll know if I were successful in October when I put the boat out of the water. I have to admit, It took a lot of work to do that and I'm very happy that a couple of friends helped me to do it. If it is of use to you I can send more details about the process and some pictures to compare with your problem.

Cheers!

Photos would be appreciated, this season I opted to not stress about it and I was going to get the boat soda blasted in the fall to see what damage lies and to let the boat dry out. And then repair if needed or get a barrier coat and bottom paint applied.

[macowneril2015]

Hi Macowneril2015!

I’m sorta more cautious than others….

If you have blisters like you describe they may ver well be actually into the fiberglass which can be a problem.
Covering them over may not be the best idea.

They may be draining “fast” because someone (or circumstance’s) have “popped” them at some point.
If I may suggest…. It’s always better to know facts and work within them than for wishful thinking.

When hauling out mark the shape and size of all the blisters you are able to see before they drain.
It might help to make a map reference to find them later on… I’ve used a tape measure in the photos from a common reference point like the stern
Observe the blisters…do they have pinhole drainage you can see?
Press on the blisters….are they stiff or gushy soft?
>>> stiff means they are gonna most likely be in the actual fiberglass and should be addressed
>>> gushy soft like partially filled baggy or balloon might mean it is only under a layer of paint … you may be lucky in that aspect

If I had osmotic blisters I would be inclined to deal with it sooner rather than later… the problem only gets worse and can affect hull integrity. We have relatively thinner hulls as trailer sailers than fixed keel boats. So not a lot of thickness to compromise. Exposing and blending and applying new fiberglass is the only relevant solution. Often they are shallow in the early stages so not too much of a task.
The void space an osmotic blister creates is generally befouled with crud and slime… nothing will stick to it so there isn’t an “injection” option that’s valid.

As far as repair costs it varies a lot and is dependent upon the actualities of the particular situation.
Dealing with known facts allows you to plan accordingly and responsibly. Good Boats like MacGregors tend to get passed down or sold to multiple owners so there is an integrity aspect to consider too. One wouldn’t want to potentially cause harm in the future if avoidable.

Now once actually fixed the application of two or more coats of barrier epoxy paint up to above your water line will generally ward off future osmotic blistering issues.

As whatever the problems may be that exist I’d want to know.
Getting the hull blasted is a good start… the photo map of the marked blistering gives you a good reference to check against once it’s cleaned.
If the blisters were only under the paint (barrier or ablative) then your well prepared for the new barrier paint coatings to be applied followed by your bottom treatment.
If the blisters are in the fiberglass then you’re at a good place to address them properly.

It’s ultimately your call on what you want to do.

Best Regards
Over Easy

Over Easy,

Thank you for this post, I will more than likely deal with them this fall, my plan was to get the boat bottom soda blasted/ sanded down and see what issues are present and then either repair myself or have someone repair and then apply a barrier coat and bottom paint. They seem firm but they all disappear which is why I didn’t notice until recent seasons when I took a hard look at hill after pulling out.

[Ixneigh]

I had quarter sized blisters on the v222 that I used to own before I got my 26. The boat was old 70’s vintage that did not have a barrier coat and spent several years in the water at one point. They seemed to be in between the hull thickness not on the surface layers. The boat was sold and then lost in a hurricane before they became an issue. Had I kept the boat I would have let her dry out a season, then taken her to a yard where they block the boat on jack stands and applied three coats of the Interlux paint brand grey epoxy barrier coat.
I’ve had mixed luck repairing the actual blisters themselves. The best repair is removing the old gel coat entirely and the affected outer layer of fiberglass, and reskinning the boats bottom with a few layers of fiberglass cloth and either epoxy or vinyl ester resin. I would probably use vinyl ester with a topcoat of the interlux grey barrier coat. I’ve seen them do pretty big boats this way and in extreme cases they remove and replace half the hull thickness. (These are large expensive yachts)
On my 26, bought new, I applied a barrier coat right away.
Ix