Blisters above the waterline

[ojk1184]

I have had my Beneteau Oceanis 320 on the hard for about 4 weeks doing some various works and when we launched today there is blistering where the stand pads were resting against the hull. I am being told by those responsible for hauling out that it's osmosis from moisture within the hull. I don't believe this is the reason and I suspect either trapped moisture / solvent on the pads causing the blistering. When I touched the blisters today they popped with very light touch.

Opinions on the below would be appreciated:

We suspect she may already have moisture in her hull, and the warmer/humid temperatures experienced on the surface in contact with the support pads may have quickened the osmosis process, resulting in the blisters.

The support pads have never been an issue for any of the previous boats we've upslipped, and we have had boats stay much longer than a month on the hard.

The durability and water-resistant properties of the gelcoat/paint may have been diminished since it was last applied, and may be further compromised when subjected to higher humidity.

 

[Tranona]

The blisters are coming from moisture in the hull and the damp pad has accelerated the process. They may well go away when the boat is back in the water.

 

[srm]

The durability and water-resistant properties of the gelcoat/paint

If you have paint over the gel coat the blisters may be due to solvent remaining in the paint film. I have seen this in epoxy coatings with blisters forming between two coats of the paint.

 

[chris-s]

My only comment it to say Hi to a fellow 320 owner!

 

[Concerto]

This looks like small air bubbles trapped in the gel coat that were not brushed out, not osmosis. Not knowing when your boat was built makes it difficult to check if this is the cause as many newer boats have sprayed gel coat and this would not apply. The reason I know of this problem is I suffer micro bubbles in the gel coat on my Fulmar. Those above the waterline, like yours, disappear shortly after launching when the gel coat has dried out.

 

[Keith 66]

I have experienced this on our Sabre 27, she was built in 1971 & in 1982 had a full osmosis job below the waterline, i believe by Berthons. Quite why this was required on am 11 year old boat i dont know!
The osmosis job was a full peel of the gelcoat & a layer of glass cloth & epoxy, It has never given any trouble & when we bought the boat around 2007 she had lived in a mud berth for 20 years. Despite this her hull was pretty dry & a moisture meter found her hull was drier than most of her sister ships in the club!
However the topsides proved problematic, I painted her with Epifanes 2 pack poly, something i have done many times with great success. I put her on a winter cradle that had a fender board halfway up the topsides on the stb side. A fender was jammed in at the stern. Come spring time there was the exact outline of the fender on the topsides, these were not surface pain blisters but extended right down to the laminate. Next year these blisters extended under the fender board too. I had to grind the gelcoat of & fair with epoxy before repainting.
The strange thing is the problem has never happened on the port side where her jetty mooring fenderboard hangs all season.
I can only surmise a bad batch of gelcoat or gelcoat contamination at her moulding stage, One grp guru i know suggested possible contamination of brushes or rollers via dirty acetone contaminated with partially cured resin or gel. He also suggested the PVC may have outgassed & affected the gel? He had seen similar cases though not very frequently. This may explain why my boat only got it on her stb side!
Since the epoxy job & repaint i have had no further problems.

 

[ojk1184]

My only comment it to say Hi to a fellow 320 owner!

Aloha

 

[Sandy]

Gosh, I have never seen any boat with the stand pads so high up the hull. Is that common in your part of the world?

 

[ojk1184]

No it's not. That's another point of contention.

 

[Stemar]

Quite why this was required on am 11 year old boat i dont know!

My nasty, suspicious mind wonders if it's because it's a great money spinner for the yard.

While I've no direct personal experience other than the odd blister on my boats that I've ground out and filled, my reading on the subject suggests that it was believed to be a problem that needed an expensive fix 20 years ago, but the general consensus now is that very few boats really need such radical treatment.

 

[pmagowan]

Also double check that previous boat on the stand hadn't been removing paint with stripper!!

 

[RunAgroundHard]

Water on carpet bearing pads was a common source of blistering on GRP dinghies that sat on hull shaped supports in launching trolleys. I first came across this on some (not all of the fleet) 420 dinghies sailed on a freshwater loch. Later I learned that a similar process happened in freshwater GRP tanks built into hulls.

Interesting reading here, but it can be a bit alarming, which time suggests has not been warranted. I think you are seeing the reactions caused by hydrolysis aka osmosis. https://montymariner.co.uk/wp-content/uploads/2014/02/Osmosis-handbook-9a.pdf

If it was my boat, I would have a surveyor who has a good reputation in diagnosing detecting and diagnosing osmosis. I would at least remove one blister to understand if it was just a paint, gel coat, or deeper, then decide from there.

 

[ojk1184]

I have had my Beneteau Oceanis 320 on the hard for about 4 weeks doing some various works and when we launched today there is blistering where the stand pads were resting against the hull. I am being told by those responsible for hauling out that it's osmosis from moisture within the hull. I don't believe this is the reason and I suspect either trapped moisture / solvent on the pads causing the blistering. When I touched the blisters today they popped with very light touch.

Opinions on the below would be appreciated:

We suspect she may already have moisture in her hull, and the warmer/humid temperatures experienced on the surface in contact with the support pads may have quickened the osmosis process, resulting in the blisters.

The support pads have never been an issue for any of the previous boats we've upslipped, and we have had boats stay much longer than a month on the hard.

The durability and water-resistant properties of the gelcoat/paint may have been diminished since it was last applied, and may be further compromised when subjected to higher humidity.

Looks like they are drying out now. Just wondering if it is osmosis would the blisters dry out so quickly?

 

[ojk1184]

Looks like they are drying out now. Just wondering if it is osmosis would the blisters dry out so quickly?

 

[Keith 66]

My nasty, suspicious mind wonders if it's because it's a great money spinner for the yard.

While I've no direct personal experience other than the odd blister on my boats that I've ground out and filled, my reading on the subject suggests that it was believed to be a problem that needed an expensive fix 20 years ago, but the general consensus now is that very few boats really need such radical treatment.

Maybe but that was long before we bought her, but the Sabre doesnt have a reputation for suffering from osmosis in fact they are usually pretty good in this respect. The weird thing was why it happened only on the stb side whereas the port side with its damp carpeted fender board has never showed any problems.