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Blisters - above water line

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szymek
Navigator

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Canada
209 Posts

Initially Posted - 04/30/2016 : 09:34:07

Hi Folks - i've bene offline for last little while but we're going back in the water this year (after 2 season break due to addition to family).

I had my boat stored outdoors and hence i knew i wouldn't be putting her in water for at 1 or 2 seasons, i decided to put a tarp on her.

i took the tarp off yesterday, and i started noticing tiny blisters in quite a few areas around the hull (above water line). i've read quite a bit about blister below water line, but i've never seen blisters above water line.

i have a feeling this was caused due to water trapped inside the tarp somehow - around the edges at the bottom.

this is what it looks like.

Biggest area is on starboard side and it's about 3' long and 6" high. On port there are about 4 cluster that are about 12"x12". All those areas were quite dirty hence i'm thinking there was water trapped behind the tarp in those areas. Fiberglass is not soft at all - just the blisters and some popped. litterally look like rash on skin.

I'm scheduled to launch May 8th - by going in the water can it make more damage?

Have any of you seen this before? does it look like i will need to get entire hull sanded and refinished with new layer of gel coat?

i'm quite frustrated - i thought i was doing good for covering the boat (first time ever) and seems i did more damage.

Daniel
Shy Tuna
1985 C-25: SR/FK/TR #4838

Steve Milby
Past Commodore

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USA
5851 Posts

Response Posted - 04/30/2016 : 11:21:23

I don't recall having seen that many blisters above the waterline before, but blisters were endemic in the boat building industry during the mid-1980s, ending in about 1989. That looks cosmetic. The amount you should be willing to spend to repair it depends on the value and condition of the boat otherwise, your personal cosmetic standards, how long you intend to keep the boat, etc. I would recommend you repair the blisters yourself, and then either paint the hull or have it gelcoated. The latter would be preferable.

I agree that the tarp probably caused it by holding moisture on the surface for long periods.

I just learned a new way of securing a tarp that I'll be using on both my boats next year. Instead of tying the tarp to the boat, or hanging jugs of water or sand from the grommets, I'm going to drive heavy duty tent stakes into the ground at just enough angle to hold the tarp away from the side of the boat. I have seen it done, and it leaves a couple inches of air space between the hull and the tarp, so that no moisture can be trapped. The owner of that boat bought the stakes at Ace Hardware, and he said they are sturdy enough to withstand hard pounding with a hammer into hard, rocky soil.

Steve Milby J/24 "Captiva Wind"
previously C&C 35, Cal 25, C25 TR/FK, C22
Past Commodore

bigelowp
Master Marine Consultant

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USA
1736 Posts

Response Posted - 05/01/2016 : 07:08:24

so . . . . am I correct in assuming that this could also happen to anyone who keeps their boat shrink wrapped over long periods of time (multiple seasons) or in high humidity areas??

Peter Bigelow
C-25 TR/FK #2092 Limerick
Rowayton, Ct
Port Captain: Rowayton/Norwalk/Darien CT

islander
Master Marine Consultant

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USA
3992 Posts

Response Posted - 05/01/2016 : 08:12:50

The only other time I saw this happen was to a friends boat. He left a welcome mat on the cockpit sole over the winter and when he removed it in the spring the fiberglass under the mat was in similar shape along with cracks in the gelcoat. Id say yes that it was caused from the tarp being pressed to the hull in that area and moisture freezing/thawing without air circulation did the damage.

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

szymek
Navigator

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Canada
209 Posts

Response Posted - 05/01/2016 : 18:23:54

I've done some reading this evening and will continue to dig in this week so I can understand it better.

As Steve mentioned - I can confirm that those blisters were definitely caused by moisture trapped under tarp and directly touching hull. Over time some minor rips developed on top and water started getting in. I specifically left stern and bow wide open so air can pass through - but i never considered water getting trapped under tarp that is touching hull. I was always under impression that gellcoat is not permeable - well that is not the case. Essentially over time water will penetrate gelcoat and hence i got the blisters.

This is how she was covered for 2.5 years.

I've had this boat since 2008 and at this point there is no plan to sell it. I've spent a lot of effort and money making modifications and countless upgrades - not to mention priceless moments on her as sailing through some rough weather, proposing to now my wife, etc.... this boat is perfect size for what i'm looking for in a boat. Finding those blisters the other day and realizing I've caused it because of the tarp, it really turns my stomach.

i'm moving from lake Ontario to Georgian bay this season and i'll look for local fiberglass guy to take a look and advice on cost to repair it. i hope spot repairs are doable and they can match colour of gelcoat - as redoing entire hull all around i'm sure would be quite expensive.

Bigelowp - you are correct, this can also happen when shrink wrapping and spacers around the hull are not used (new to me).

Daniel
Shy Tuna
1985 C-25: SR/FK/TR #4838

Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts

Response Posted - 05/01/2016 : 20:21:43

When we bought our C-25, it had some pin-head sized blisters in the boot stripe, which the surveyor said were caused by algae fostered by lapping waves, and not to worry about it. I know that with coatings like Awlgrip and Imron, spacers must be used to keep shrink-wrap or other plastic tarps off the surface. I haven't heard of this problem with gelcoat, including on my current boat, although its hull shape probably keeps the shrink-wrap off the gelcoat from the rub-rail to the bottom-painted hard chine.

Funny story about permeability: I have a Diet Coke can that has never been opened over I don't know how many years, and is completely empty of any liquid. Apparently the water molecules migrated through the aluminum and are all gone. Who would've guessed? I also have had plastic water bottles, never opened, that partially collapsed due to the loss of water after a year or two... Water migrated out, but air didn't get in, and a vacuum developed. 'Splain that!

Hope your repair isn't too extensive.

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

Edited by - Stinkpotter on 05/01/2016 20:30:50

islander
Master Marine Consultant

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USA
3992 Posts

Response Posted - 05/02/2016 : 04:15:21

Fiberglass and gel coat are not waterproof. Given enough time water will permeate it causing blisters. Your cover was on for a long time but the average winter stored boat won't see this happen. Same goes for boats that are left in the water year round. They usually end up with hull blisters. Boats that are hauled and stored seasonally get to dry out and usually are blister free. My winter cover only comes to the rub rail so there is plenty of air circulation. Trying to fully cover the boat might not be the right thing to do. Heartbreaking for this to happen.

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

Steve Milby
Past Commodore

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USA
5851 Posts

Response Posted - 05/02/2016 : 05:21:54

I covered my 1981 C25 with plastic tarps for many winters without that problem, but boats built between about 1984 and 1989 are the boats at risk. Nothing should be left on them anywhere that might trap moisture. A pioneer in the fiberglass industry told me that water is one of the most invasive substances known. Given enough time it can penetrate almost anything; fiberglass, iron, etc.

Steve Milby J/24 "Captiva Wind"
previously C&C 35, Cal 25, C25 TR/FK, C22
Past Commodore

Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts

Response Posted - 05/02/2016 : 06:12:28

Also, fresh water permeates more readily than salt water and other solutions. Hull blisters are much more prevalent in fresh water (e.g. trapped rain water). Once the water gets under the gelcoat, it reacts with the fiberglass resin to create an acidic soup that strongly attracts more water through the gelcoat (osthmosis)--so strongly that it creates the pressure under the gelcoat that makes it blister out. [/chemistrylesson]

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

Edited by - Stinkpotter on 05/02/2016 06:13:40

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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.