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Old 02-19-2008
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Question Theory on cause of Fiberglass Hull Blisters

Theory on cause of Fiberglass Hull Blisters

In looking over lots of information here on sail.net and other places about fiberglass hull blisters I have come to a theory of the cause that I want to run by you guys. I really want your input on this as it seems logical to me. Maybe I am completely wrong and maybe I am on to something… Give me your input please.

I have never known of a Jacuzzi to blister at all. I called several suppliers and asked them if they have run into the blister problem, and NO they don’t or they rarely do. In their experience the tubs and pools tend to blister when water gets behind the un-gel coated fiberglass steps or areas. They are made of the same materials as these yachts and they sit with water on their finished surface all the time 24/7 like yachts. The only difference with Jacuzzis is they are chopper gun shot with no core usually. Standing water never gets to the un-coated side at all.

Now, after looking over 250+ pages of information and links all over the net about fiberglass hull blisters it seems most people are pointing to this as a cause:

#1 – A boat made between 1975-1989 has more problems because of the oil shortage problems caused to chemicals to be changed.

#2 – A boat that is never pulled out for regular cleaning & waxing of the hull will have more problems.

#3 - Sand blasting / Sand washing of the gel coated fiberglass hull causing micro cellular openings allowing water penetration.

#4 – A chopper gun shot hull that was not hand laid up causing poor bonding & blending of the fiberglass resin with the strands.

#5 – Leaking port holes and other areas that are letting water inside the boat and between the layers of the fiberglass matting and core. ( this seems real common).

#6 – Older boats that only have gel coat on the outside and finished areas inside the boat will have more problems (1975-1989) usually verses newer boats that have gel coat on every inch that have much less problems…

Several companies make big bucks repairing blisters and it would be in their best interest to NEVER fix this problem for good. They recommend complete peeling of the gel coat and re-application after re-lamenting by hand. Several horror stories have been posted on this site and others by people that have had this done to their yachts, and about 50% of them that I read up on this type of expensive treatment only seems to work for about 2-5 years.

Now, after reading lots of posts and websites to learn as much as I can about yachts before I buy one I have come to a theory.

========

FACT:
Almost all fiberglass yachts have blisters, and almost all of them have standing water in the bilge that they say is too low to pump out. Reading further on the forums I have learned that it is a good idea to have 2 bilge pumps one small as low to the bottom as you can get and one large above it for a serious problem. Both should have trigger counters on them to count the cycles they are used.

FACT:
The packing nut for the prop shaft should be allowed to slowly drip approximately 2 times a minute. This water has no where to go but down to the bilge to stand until it is high enough to activate the pumps.

========

You would think that you would not want water to stand in the bilge, you would want it dry. Because you need this dripping packing nut for lubrication of the shaft I would think it would be a good idea to fix this water to its own standing pool area that is treated with gel coat and a small pipe with a hose in the dam area where it can be allowed to work its way into another sealed small bilge pump bucket and not allowed to just work its way down into the bilge to stand. This along with fixing all the other sources of water intrusion and holding should keep your bilge fairly dry. If condensation is a problem the use of fans and vents in the bilge area would greatly dry the dampness.

Thinking back to college physics and the problem that water is causing to the fiberglass once it is past the gel coat brings this up into the mix… Maybe it is not coming from the outside at all or at least in most cases… Since you would never want to expose un-gel coated fiberglass or a popped blister on the outside of the hull to water why would you expose the un-gel coated fiberglass inside the bilge bottom to standing water? My theory is that it would be possible for the water in the bilge to work its way to the outside of the hull since liquids will tend to want to move to the heated areas “cold to hot” attractions etc… Water in the hull would find its way to the other side of the fiberglass hull and would then work its way up the outside layer in a gas / vapor type state because of the being heated by a sunlight warmed hull, and turned into vapor until it cools enough to find an area that is week, condense again to liquid and press out. Thus the outside hull blister would then appear. Newer boat builders are gel coating everything inside and out, verses older boat builders that only did the finished “showing” areas.

What do you guys think about this?


Travis E. Towle
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Looking into the 1974 era Gulfstar’s Center Cockpit 41’ – 55’ Ketch’s or Sloop’s
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Old 02-19-2008
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It's not just older boats, in Gemini's hull numbers within 10 of mine have reported hundreds of blisters within 2 years. I don't know on mine yet as I've not pulled it (it will be one year old in May).
It's chemical, quality and water ingress combined IMHO.
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Old 02-19-2008
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Guess it many things

I remember years ago I had gone to Ocracoke Island off the coast of North Carolina.

I bought a Bumper Sticker to put on my Truck. I put the sticker on the back glass window that fall when the weather was cool and it looked good to me.

The next summer the bumper sticker had these little bubbles (Blisters) everywhere.

It have something to do with applying the Gelcoat into the mold and then how the Fiberglass is mixed and/or applied. Temperature, Moisture in the Air etc. Many things could have possible affects, I guess.
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Old 02-19-2008
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"The cause of the problem was well established in the 1987 University of Rhode Island study by Thomas Rocket and Vincent Rose, The Causes of Boat Hull Blisters. In simple terms, what happens is this. Water penetrates the gelkote both as water vapor and as liquid water. Water is particularly good at this due to the small size of the H2O molecule. The gelcoat is a rather poor barrier against water penetration when constantly immersed. The glass fibers assist by acting as capillary tunnels to transport the water molecules into the laminate. Once adjacent to the resin in the gelkote and laminate, the water goes into chemical solution with what are known as "water soluble materials (WSMs)" in the resin in the gelkote and laminate. These WSMs include phthalic acids, glycol, cobolts, mekp and styrene which have not gone to full cure in the hardening process. To varying degrees they are present in all cured polyester resins. Five percent is an excepted norm. In some rare cases the quality of the materials or their application may be inferior causing a higher than normal percentage of water soluble elements."
More here: http://www.zahnisers.com/repair/blister/blister1.htm
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Old 02-19-2008
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Thanks for that posted link - that is one article I have already read a dozen or so times. They say "Water penetrates the gelkote both as water vapor and as liquid water. Water is particularly good at this due to the small size of the H2O molecule. The gelcoat is a rather poor barrier against water penetration when constantly immersed."

OK there is a PROBLEM WITH THAT CONCLUSION:

If this were really the problem you would see this damage on every one of the gel coated fiberglass Hot Tubs, Jacuzzis, and Swimming pools - and you don't! NEVER!!! You just don’t ever see this. So that fact and conclusion of that study is VERY WRONG and can be proven as so today. I am fairly sure that NONE of the students working in and around this study had the balls to stand up and say “Hey Professor you forgot something… Fiberglass Hot Tubs and Swimming Pools don’t have this problem! So your theory is in-correct.” Well, if they did they would have probably flunked that class…

===========

It bothers me too that the article is linked to their "repair" area of and they clearly state "To help our customers better understand the matter, we offer our Blisters & Laminate Hydrolysis on-line." Note “OUR”. I hate to sound like a conspiracy theorist here but if you thoroughly research this subject like I have you will see that their stated repair method does also fail. They also say “The coating should be inspected annually for evidence of failure. Failure will usually be evidenced by blistering of the barrier.” No really? If their repair worked and this was really the “way” to do it then there would be no failure because they have addressed the problem as they stated it was. If they were really confident that they had this problem licked they would not have posted this “Zahniser's offers limited warranties on all bottom repairs.” If the problem is really licked and was caused by what they said it was, and they fixed it – they should post an absolute GARENTEED FIXED warrantee. I would be interested in seeing the actual study report and will look for it. But remember studies can be leaned in any direction the person paying for the study wants it to. Heck in Texas you are a bad driver if your FICO score is too low. Last time I checked FICO had nothing to do with how good I steered my car?

I am not slamming any company or study, I am just asking questions… They do have several points:

#1 - Preventative maintenance is simple in principal: KEEP THE WATER OUT OF THE POLYESTER LAMINATE!!!

#2 - Barrier coats, because they are much less porous than gelkotes will blister with less moisture.

With point #1 + #2 you would think that part of the cause just might be water in the bilge seeping into the glass from the inside?

====================

Gryzio pointed out that it might have something to do with applying the Gelcoat into the mold and then how the Fiberglass is mixed and/or applied. Temperature, Moisture in the Air etc. Many things could have possible affects. This sounds reasonable but if that were the case you would have Kit Cars, Corvettes, Lotus’s cars and smaller sailing boats like Lasers and C-Scows with this same problem. NONE of them do. But none of them have standing water. Then you have pools and Jacuzzis, they have standing water, but again no blisters.

IN CONCLUSION:
With my theory it would seem the problem would lay in the fact that water is getting into the laminate from the inside of the boat. A problem could also lay in the fact that these bigger yachts have a core inside them and are not solid fiberglass. Everything I listed above, the cars and Jacuzzis don’t’ have cores either.

Does anyone else have any other thoughts or ideas of what might be a hidden cause that I have not thought of?


Travis E. Towle
Topeka, Kansas

785-357-1004
Looking into the 1974 era Gulfstar’s Center Cockpit 41’ – 55’ Ketch’s or Sloop’s

Last edited by travistowle; 02-19-2008 at 10:48 PM.
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Old 02-19-2008
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Quote:
Originally Posted by travistowle View Post
Theory on cause of Fiberglass Hull Blisters

My theory is that it would be possible for the water in the bilge to work its way to the outside of the hull since liquids will tend to want to move to the heated areas “cold to hot” attractions etc…
I don't understand this "cold to hot" attraction. It seems fundamental to your overall theory.

Can you explain this a little?

Thanks,
Craig
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Old 02-19-2008
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You already have the cause. You just refuse to believe it. The study referred to was actually done by the University of Rhode Island paid for by the US Coast Guard Office of Boating Safety. I worked in the Office of Boating Safety at the time although I was not the project officer on this particular project.

A copy of the complete study can be purchased from the Defense Technical Information Center (I tried to post the link but I don't have enough posts according to the error message I got. But if I get an -email or pm I cna give it to you)

The cause is known. What the real question is, What is the cure? Numerous yards, repairers and marine centers have become supposed experts on curing this problem. FRP is a semipermeable membrane, so you simply have to find some way to prevent it from acting as a semipermeable membrane.

The generally accepted method is:
Take the boat out and let the laminate dry. (this can take a long time)
Completely strip off the gel coat and as many layers of glass as necessary
(this depends on the extent of and depth of the blistering because contrary to their popular name "gelcoat blisters" they do not occur in the gelcoat, they occur in the laminate and can be just the top layers, or go clear through the laminate. Some are a total loss.)
Replace the laminate
Replace gelcoat or not (some do some don't)
Apply Barrier Coat (typically some sort of expoxy barrier coat but this varies depending on who's doing the repair.)

Hope they don't come back. Very often they do.

And oh by the way, yes blistering does occur in other fiberglass structures but most fiberglass structures are not continuously submerged in water. The warmer the water the worse the problem. I have seen a boat that was six months old with blistering so bad it was a total loss, and on the other end boats that are 40 or more years old with no blistering. The old navy launches built in the 40's out of FRP and built about 5 times heavier than anything built of FRP today have never (as far as I know) blistered. And many of those old launches are still around and being used daily.

It does have a lot to do with the types of resin and the quality of the layup. But mostly it has to do with how much is cured and how much isn't. It you have a lot of uncured resin in the laminate you're going to get blisters. I once looked at a swan that had one of the heaviest lamiantes I have every seen on a boat that size, and gel coat that was twice as thick as normal, and it was very thoroughly blistered. It had been berthed in the Potomac for years. Maybe it was all that pollution! LOL.
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Old 02-19-2008
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Travis...of course zanheisers has a commercial interest in publishing that info...but it is based on an academic work that you should be able to track down and perhaps the authors Rocket and Rose are still at URI and would respond to a question.
My own guess would be that bilge water has little or nothing to do with it since blistering is often far removed from the wet portion of the bilge and many bone dry hulls get blistes as well.
Since we don't KNOW tha hot tubs are made of the same fiberglass and gelcoat materials in the same way and since the water in them is treated as well...we may not have the same chemical reactions that result in blisters taking place.
I do find more boats down south seem to have blisters and of course they aren't hauled during the winter typically so the continuous immersion explanation makes sense to me from a layman's perspective.

EDIT: Professor Vincent Rose is still at URI and here's his web page and e-mail link: http://www.egr.uri.edu/che/Faculty/rose.html
E-mail: rose@egr.uri.edu
He also has a patent on preventing them!
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Old 02-19-2008
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Travis -- Some comments on your posts:

Water in bilges has long been linked with blisters. Sorry, but others beat you to that observation. But if bilge water was the prime cause, then one would think the blisters would only be found in the fiberglass surrounding the bilge. In my experience, blisters usually are spread out and not confined to one spot (although they can be on some boats.) And yes, dry bilges are desirable for a number of reasons -- smell being one.

In the early 1980's some manufacturers started using vinylester resins, which are much less porous than polyester resin nearly everyone used previously. For example, Pearson started using vinylester resins at about that time and offered a warranty (I think it was 5 years but it could've been 10) against blistering. the gelcoat Pearson used was made by Glidden using the trade-name Blister-Bloc. It did it's job. I did a barrier coat job on my 1988 P-33-2 in the spring of 2006 due to blisters finally showing up.

Your point about jacuzzi's and such not blistering -- here's one manufacturer that does talk about blistering being a common problem:

How are spas constructed?

Most manufacturers use the fiberglass lay-up method of spa construction. This manufacturing method combines layers of polyester resin and glass fiber. A heated acrylic sheet is placed over a spa-shaped vacuum mold. Air is drawn out through hundreds of small holes. When the acrylic cools, they remove it from the mold and reinforce the underside of the spa with a resin and chopped fiberglass mixture. This polyester resin and glass combination can lead to a common problem—acrylic blistering. Blisters occur because of a chemical reaction between moisture from the tub and the polyester resins used in the reinforcing process. Many spas have been ruined because of blisters. Spas made from polyester resins not are blister resistant. Their finish and structure warranties are separate. The salesman points out the structure warranty because it is usually 10–15 years. Many times he won’t mention that finish warranty is only 1–3 years. You could have a blister problem in as little as one year! Great Northern spas don’t have the blistering problem that others do because we use epoxy resin instead of polyester resin to reinforce the spa. Epoxy resin doesn't’t react with moisture to form the gasses that cause blistering. Great Northern spas are blister proof. The warranty on structure and finish is the same—20 years.


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Old 02-19-2008
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A major flaw in your theory

is the fact that blisters only occur below the water line and in areas well above and away from the bilge..I have blisters on my rudder
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