Osmotic Hull Blisters

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Osmotic Hull Blisters

Postby rob » Fri Nov 30, 2007 12:52 am

Christal, sorry to hear the woes of Seaventure's hull. It is probably not too bad though, just depressing when you find something like that. Elsa has blistering. I found two or three big blisters on the hull towards prop/rudder area. They came up after a few days out of the water. I popped them letting out high pressure acetic acid smelling liquid. I then set too with an angle grinder (nasty machine) and cut out the blisters. Very easy using the grinder with a cutting disk tho lots of care needed. A few days left the exposed surface nice and dry. I then filled the holes with epoxy paste. When cured I sanded it down smooth, and coated with primer ready for antifouling.
There was one about 3-4 inches in diameter on the stern just below water level. I left it untouched as a control, suspecting it would go down again when she went back in the water - and it did. There are voids beneath the gelcoat where the blisters form, where the original resin has not cured or has impurities, bubbles of air etc. It seems the osmotic pressure is balanced somehow when the hull is in the water.
I wonder if yours are the same problem?
Elsa also has hundreds of pinhole mini blisters on the surface of the gelcoat. Some go through the gelcoat, but all of them are dry and open. Most of these are around the shaft area and were hidden under the antifouling and were only found when I tried scraping the antifouling off. I rubbed epoxy filler into these too. I suspect these may actually be bubbles in the gelcoat when it was put into the mold!
Elsa had an epoxy coat put on around 1990 and the preparation for this was very poor. In places it can be peeled off by hand leaving traces of antifouling underneath!!! Poor Elsa.
One day, when we can afford it we will give her the full treatment, ie get the gelcoat peeled and have a proper epoxy coating applied.
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Re: Osmotic Hull Blisters

Postby claire » Fri Nov 30, 2007 2:11 am

Hi, I thought I'd split this off into a topic of its own cos it probably affects a few of us. I was chatting with one potential Krogen 38 purchaser a few days ago whose survey showed up blisters & that boat is getting its hull peeled, re-gelcoated and epoxied. Interestingly their quote in the US was ~$8000 USD. Here in the UK we were quoted £10,000 GBP 2.5x as much! We live in the wrong country :)

I didn't want to interfere with your seaventure projects thread Christal, so have left your blister post where it was, but here's a link to it:
http://www.yacht-elsa.co.uk/forums/viewtopic.php?f=3&t=30#p119
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Re: Osmotic Hull Blisters

Postby Seaventure » Sun Dec 02, 2007 10:03 pm

Well I guess misery loves company, so while I don't wish hull blisters on any boat owner, at least we're not alone in this type of project.

Interesting to hear the money involved in fixing the blistering. With all we have going on right now, those prices just wouldn't be doable for us. We'll have to be VERY nice to our friend who's going to work with us on this! He's quite the perfectionist so don't know how it will all work out, as the yard we are at won't let anyone do much grinding/sanding....we need to keep it low key. We're hoping he'll be able to start helping this next week.

When digging around under the shaft area we actually dug away most of what I call a wing piece on one side. Good thing our friend is quite the fiberglass wizard.

Many of our small blisters didn't seem to be very deep either and wouldn't have been noticeable at all. Others we were an inch or more across...

At least we're not pulling any more water out of the hull with the wet/dry vacuum cleaner.
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A Krogen Hull getting peeled.

Postby claire » Sun Dec 02, 2007 11:11 pm

Here are a few photo's we've been sent of a Krogen 38 in the process of getting it's hull peeled. Anyone interested in seeing higher res photo's please drop us a line.

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Re: Osmotic Hull Blisters..Seaventure progress

Postby Seaventure » Thu Dec 06, 2007 2:53 pm

And the grinding continues on our hull. I talked with the seller of the boat last night and our friend doing all the hull repairs. Of course they both had completely different views on dealing with the blisters.

The seller said that he had dealt with treating hull blisters in several boats he'd owned over the years and had never been that successful in completely stopping them. So when he saw that Seaventure had them he just popped the obvious ones seen during a haulout (to relieve the pressure) and left them alone. After 3 - 4 years he said the boat stabilized and he seldom saw any more. He could see that over the years in some places the same spot had been treated several times. Hmmm.

Of course our friend with all the fiberglassing experience completely disagreed with this theory. You can just imagine! He feels very strongly that it's quite important to try and resolve the water logging situation as it eventually deteriorates the fiberglass. Yesterday they discovered one spot that just kept oozing and oozing and finally used the wet/dry vacuum to pull moisture out....and out it came. Our friend Mike said there are about 8 fairly bad spots and one (besides the wing area that my husband Burt dug at already) that will require fiberglass to fix. I remember in one of those articles about the history of the Krogens that they moved from one yard to another after a few years because of quality issues. Well Mike had several comments about whoever was in charge of dealing with the hull...nothing horrible but there appears to have been a learning curve. I wonder how hull #1 has faired over the years.

Anyway it's a massive job for our friend Mike, with Burt helping as he can between the other projects. Mike has already figured out that he'll be here for at least another week.
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Re: Osmotic Hull Blisters

Postby Seaventure » Wed Dec 12, 2007 9:14 pm

The person who sold us our boat sent this website recently. It's what he based his approach on for dealing with Seaventures blisters. Anyway it's interesting reading: http://www.zahnisers.com/repair/blister/blister1.htm- naturally our friend helping us with our hull still disagrees.
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Re: Osmotic Hull Blisters

Postby claire » Fri Dec 14, 2007 1:48 am

That's a brilliant article Christal. I think it's the clearest and most convincing one I've ever read, for the first time I thought 'Ah ha - Yes, I understand that now'. I'm surprised though that the person who sold you Seaventure thinks it supports the popping and leaving of blisters? The way I read it, it says the opposite? According to that article, popping the blister would relieve the osmotic pressure, but it would then allow uninhibited hydrolysis of the resins in the hull which would lead to an accelerated weakening of the hull structure?

Another thing that struck me in that article was that it said that this weakening by hydrolysis could potentially result in faster failure of hulls with core construction, and once the core is saturated it is usually economically unviable to repair the boat. .... the Krogen 38 is of core construction, but the core is closed cell PVC foam though so can't become saturated in the first place? I'm assuming the article is referring to boats with a balsa core?

It's disheartening knowing that having a boat in the water is resulting in a relentless gradual weakening if its hull, but I guess it's just something that has to be accepted - with GRP boats it's hydrolysis of resins, wood it's rot, steel it's .... well hydrolysis again I suppose (metal salts & water? is that hydrolysis?). ... but with all of them there are remedies, wood: new planks, GRP: new laminate, steel: new plates. We are lucky with the Krogen 38 that the hull is no darned thick in the first place - Modern GRP boats certainly aren't built that way. The surveyor who did our pre-sales survey told us that he thought Elsa was built in the days before manufacturers started doing the sums to calculate just exactly what they could get away with in the lay up. :) They were still thinking about quality & safety

Anyway, whichever way you look at it there's no escape from entropy, just an endless battle against it, with boats, houses, gardens, roads, flood defenses etc etc ... Hull blisters are just more of the same.
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Re: Osmotic Hull Blisters

Postby rob » Fri Dec 14, 2007 8:20 pm

It is a good article. I found another, giving a very different view, that also makes a lot of sense. So which one is true?
Perhaps they both apply to some degree........
http://www.yachtworld.com/offshoreatlantic/offshoreatlantic_7.html
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Re: Osmotic Hull Blisters

Postby Seaventure » Fri Dec 14, 2007 11:11 pm

Rob - I think what you are saying is true.

I think our boat seller decided to only pop the blisters as his theory was that water permeates thru the hull no matter what so why keep grinding/repairing the blisters that appear. Our friend Mike feels that epoxy is a barrier and that applied properly, water won't permeate thru it. He's filling the blister cavities with something called flux?, along with some kevlar bisquits (for the deeper spots), and epoxy resin at this point. We should invest in the company producing the epoxy resin we're buying :).

The link you posted is quite interesting reading. I'll have to print that one and have our friend Mike read it also.

I think our Krogens have good strong thick hulls and will last a long time no matter how we deal with those blisters.

At least we're into doing some filling....not just grinding away and enlarging holes! Mike wants to get all the remaining bottom paint off so we've tried several approaches. The most recent one being to lather on paint remover and then carefully use a pressure washer to take it off.
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Re: Osmotic Hull Blisters

Postby Seaventure » Fri Dec 28, 2007 3:25 pm

Just thought I'd post this article link for people who might be thinking of having their hull peeled, etc by a boat yard: http://www.yachtsurvey.com/BlisterRepairFail.htm Not that there aren't many reputable companies doing that type of work but it's interesting reading.....

At this point we realize that we probably should have invested in a planer right at the start, but the worst of the grinding is about over for us now. Now it's more of the applying epoxy resin, cotton flock (not flux as I originally thought), and the kevlar pieces.
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