How bad are blisters?

[WadeWest]

Am considering the purchase of a 2004 Carver 396. The boat has hull blisters below the waterline. Seller says they are caused by interaction between some chemical components in the gel coat and the fiberglass, as opposed to an indication of "waterlogged" fiberglass or other problem. Does anyone have any experience or advice regarding such blisters? Do they create a hull weakness problem? Thanks for help.

[Tireless]

Blisters on the hull is not a good sign as it could be osmosis. I had blistering on the hull of my previous jet boat and it was osmosis.

Need to have a qualified boat surveyor examine the boat structure, he should know what’s going on.

I have never heard about chemical components in the gel coat and the fibreglass and I would be suspicious. If that was true it would happen more often and as I stated, never heard that one before.

May have to grind one off and see what’s going on in there.

If it is osmosis, it can be repaired by having a fibreglass guy epoxy the hull after it has be cleaned up.

Hope this helps.

Greg

[Midnightsun]

How bad are blisters? BAD, BAD, BAD!!

One of my older boats (a 28' express) had slight blistering on the hull after a survey. I was selling this boat to move up. Cost me $6,000 to have this repaired which was back in 2003 so I assume the cost today would be quite a bit more especially on a boat that size. Point is this needs to be looked at carefully and repaired properly. The line about chemical is BS, 99.9% sure this is osmosis. Have a specialist determine what it is and what needs to be done and then how much it will cost to repair.

The process of repair is rather elaborate as can be seen here and therefor the high cost. Very long article but the first few pages will help you understand what Osmosis actually is. https://www.westsystem.com/wp-content/u ... ention.pdf

[Viper]

Welcome aboard.

There is a chemical reaction component to all this. First one needs to realize that fiberglass hulls are typically laid using polyester resins. They and the gelcoat coating are water permeable. How permeable depends on many factors but it's the water permeating the gelcoat and the fiberglass substrate that eventually trigger a chemical reaction as it breaks down the water soluble components in the substrate. The byproducts of this chemical reaction can spread through and weaken the bonding properties of the substrate and serve to weaken the structure throughout. Some studies have also determined that this chemical process can also occur in the fiberglass layers without the influence of water permeation.

Having said that, it's not very common for blisters to be of a structural concern unless they're left unchecked for extended periods and allowed to worsen to a point where the substrate's integrity is affected. The kicker is that it's not always evident and could be going on with no evidence of blistering. So this could be any boat you look at even if you don't see blisters. Your climate will play a huge role in how bad things can actually get. While heat compounds the issue, freezing temps such as where I live can be a real problem for trapped water in blisters and further into the substrate layers.

While blisters usually aren't a structural concern, their appearance is a red flag to potential buyers and typically affect the purchase price of the vessel. Once they see them on the hull, most will walk away thinking the worst even though it's usually a cosmetic issue in most cases. Having said that, this cosmetic issue is a very expensive fix. The materials to remediate the condition are expensive and the labour is intensive. The final process to this remediation before applying an anti-fouling paint is to apply several coats of an epoxy barrier. This is done because epoxy is not nearly as permeable as the gelcoat and polyester in the original build. One needs to consider though that an epoxy bottom job, even a proper one does not prevent the reappearance of blisters or blisters appearing due to a pre-existing condition in the substrate prior to the epoxy fix.

All fiberglass hulls no mater the brand are susceptible to this condition. The variables affecting/contributing to the problem are many, so while a boat may not have blisters now, it doesn't mean it's immune from them and one should be inspecting the hull annually for their signs. If a vessel already has blisters, chances are likely that the condition is only cosmetic at this point but a budget and timeline for correcting the issue should be considered eventually. The longer it's left, the more expensive the repair will be. A good fiberglass tech can evaluate and advise on the best course of action based on observations. Don't let anybody do a patch job, the entire bottom should be treated.

BTW, every fiberglass boat should have a barrier coat applied to its bottom whether there are signs of blistering or not.

Good luck with your search and keep us posted.

[Tireless]

Viper, very interesting read. This is exactly what they had to do with my old jet boat. It was repaired under warranty and I sold it.

Greg

[Cooler]

Viper - you should publish that post as an article in a boating magazine. Great explanation. The only thing I would interject is, typically, the fluid inside those blisters is not water, but more of an acidic fluid. One must be careful and know what to do with relieving those blister pockets and then repair.
Wade - you will need to get an understanding of how long those blisters were there, as well as if they were recurring events. Good luck! er

[Viper]

Source of the post.....typically, the fluid inside those blisters is not water, but more of an acidic fluid.....

Really depends at what stage the process is at and the condition of the blister. If a blister has cracked for example, chances are it's now filled with water more than anything else though that chemical process is still going on.

Blisters aren't really that scary to me but I know how to carry out the repairs so all it costs me is my time and materials. Paying someone else to do it though is pricey and you have to hope they know what they're doing. I got a boat for a really great price years ago because of blisters. I worked on it every night for a couple of weeks and ended up with a hull that was better than factory but it is a lot of work. I've done many of these jobs over the years and have yet to see blisters so bad that it caused a structural concern.

Another thing you have to consider is that a lot of insurance companies won't touch a boat with blisters which is dumb as again it's usually not a structural concern. I think their fear though is that the owner will leave it unchecked which under the right conditions could lead to a failure and an insurance claim. It just seems weird to me though that they can refuse to issue a policy based on something that is likely at the time only a cosmetic issue. With that, there's nothing preventing them from using that logic with a lot of other systems.

[edrabun]

Just had a survey done yesterday on a 94 370. Surveyor found 6 blisters. He said he expected many more and said he wasn’t too concerned with what he found. Boat had bottom paint 3 years ago. He recommended waiting two years and then pulling boat out to fix and repaint. I have no knowledge just telling what he told me. I was impressed by his knowledge and attention he gave to his inspection, so I trust him. Yes

[bud37]

I think perhaps salt water vs fresh vs tropical areas may affect these things. It is true that some boats get them worse than others for some reason or another.....is there a luck of the draw component here or is a build issue/material quality concern.

That said I have repaired them. on one new boat that blistered the first year...... ... did a complete epoxy job with interprotect, saw that boat 25 years later and the bottom was as I had just done it, clean and smooth.