We again suffered from blister problems on this haul-out and we spent some time learning about it from fellow cruisers and experts in New Zealand. We actually feel a lot better about our situation and we think it will diminish as a problem over time. In the hull we had about 40 blisters total which is a fraction of the number we had last time. It is likely that these blisters had started before we treated the bottom with barrier coat and that the barrier coat helped considerably.
We are going to describe what we learned about blisters and there will be people, even people we consulted, that will disagree with our conclusions. Blisters are one of the great debates on yachting, like Marine SSB installation, where you have to compile many different perspectives and draw your own conclusions. These are our conclusions.
When I said we had 40 blisters I didn't mention that we had 4 times that many on the rudder alone. The rudder had not been prepared correctly during the previous haul-out and more importantly it had a much more severe problem with the lay-up. When a fiberglass boat is built using a mold the first coat of fiberglass and resin are critical. If it has voids, pockets of fiberglass that are not filled with epoxy, then these will absorb water and cause blisters. Improved barriers coats, like vinyl based epoxies, will slow the water intrusion but eventually there will be a blister.
We had our rudder stripped down to the first layer of glass and we found it covered in these voids. Our solution to the problem, as recommended by Brush Strokes, was to wash the rudder repeatedly with fresh water and then coat the rudder with several coats of thin epoxy to fill the voids and seal the rudder. Then it was coated with 4 coats of barrier coat to slow water intrusion. We will see how this performs and report on the progress.
For the hull we just ground out the blisters and filled them with 2 part epoxy filler and coated them with barrier coat before we applied bottom paint. The number of blisters we have had in the hull is really not bad and this time it was much better. Our understanding is that blisters usually start to show up in a boat when it is about 10 years old and usually you have repaired most of them by the time it is 20 years old. This combined with what we saw of the voids in the rudder has led us to conclude that a boat has a finite number of blisters laid in at time of manufacture in the form of voids and once these are repaired the problem diminishes.
Island Packet prides itself in their careful lay-up and I can believe it from what we have seen in the hull. The rudder isn't a shining example but mistakes happen and our boat was produced when they were not too many years old. The quality of the lay-up is the biggest factor in future blister problems and the fancy coatings will only prolong the problem. A technique that is used to remove the voids is vacuum bagging and this probably helps but I believe a sloppy job even using this technique would leave voids. Once you have a boat with blisters the key is to repair them. If it is a big problem then you may peel all of the coating off of the hull to the first layer of fiberglass and replace it with care to fill the voids or if the problem is not that big then you can just spot repair each time you haul out and the it should diminish each time. It is nothing to panic about and if it gets you down, just be happy you don't have rust or rot.
Update from 2000 haul-out. We only had 4 blisters and none in the rudder. They were all small. We seem to be on top of it and we are pleased with out strategy so far.