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
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.