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Old 28-02-2009, 10:28   #1
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Blister experience?

Looking at a boat I might buy, which is competitively priced, but not cheap. However, it has some blistering around the stern.

When I dig into the boats history, the blistering was spotted more than 9 years ago, but nothing has been done about it in the meantime.

Obviously, if I go for it I will have a full survey done. But, should I proceed on the basis that it isn't a big problem, or should I be a bit more concerned about it. Will this have much of a difference on what I pay for it?

The boat is from a reputable quality builder (Nauticat) but is of 1989 vintage.

My concern is that left alone for 9 years, could the wet stuff have permeated deeper into the hull?

Anyone got any thoughts?

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Old 28-02-2009, 11:17   #2
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It's really difficult to offer sound advice without seeing it but generally, blisters over a relatively small area are not a show-stopper. If it were me, I'd make the offer subject to survey and have the owner fix the area using methods you approve rather than simply touching up the individual holes. Many people panic over blisters which is an over-reaction, usually.

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Old 28-02-2009, 11:28   #3
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I agree with S/V. Blisters are bad, but they can be repaired. The survey should give you a good idea of the $ depth needed for the repairs..
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Old 28-02-2009, 11:33   #4
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When I bought my current boat about 4 years ago, I went through the same thing. But I didn't find out until I had by offer in and had it up in the travel-lift for the survey. I was kind of pissed that the owner didn't give me the heads up and the broker said he new nothing about it. So I had the yard estimate the repair cost. I'm not sure how long it was like this but they told me I could put off the repair for quite some time, maybe 10 years or so depending on how much they grow. They were the size of quarters and haven't changed much since then.

So before I finalized the deal, I took a walk around that yard and another yard and noticed that maybe 8% of the boats of this age had them. After talking to quite a few people, most of them said I could leave them alone for now or I can fix a square yard every time it's out for bottom paint (I'm not sure about that, because it needs to dry out after grinding). Most didn't think it was a big deal as long as they are not burst or open. I adjusted my offer by $5,000 because of this and the owner went for it. The yards quote was quite high $20,000 to fix it, but they would peel it and re-do it completely. I decided I could do it myself by grinding each one out and repairing when I had the time in the future.

I'm still happy with my decision and I wouldn't shy away from this problem. There are other problems I would not touch with a ten foot pole.

By the way, I like Nauticats and you might be able to knock off a good chunk of money because I think lots of people will shy away from this problem.
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Old 28-02-2009, 13:58   #5
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I have a 1985 Nauticat and it has a few small blisters, they haven't changed in 5 years and i wouldnt waste my time or money dealing with them, you are talking a handlaid hull of ample thickness and the blisters are purely a cosmetic issue easily solved by putting your boat back in the water, Our nauticat is currently up For Sale and I,m quite happy to inform any purchasers of there existence. we have really enjoyed owning our Nauticat and i wouldn't let a few blisters put you off owning one.
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Old 28-02-2009, 14:34   #6
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Both my present and prior boat had blisters below the waterline. The present boat had a dozen or so primarily on the keel. The prior boat had literally hundreds the size of a pencil or a dime. For the prior boat with the pox, the bottom was sandblasted. The worst were ground out and filled with long fiber epoxy. Fairing compound was applied and sanded. I then put 5 coats of Interlux barrier coat epoxy on in one day ( to eliminate sanding between coats) as well as a coat of bottom paint. The next day I came back and finished the bottom paint. My friend still owns the boat and after more than 10 years there is no sign of blisters.

My present boat, since it was less severe simply had them ground them out and filled. Now after 8 years there is still no sign.

I tend to think that they are extremely common in sub-tropical to tropical waters.

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Old 28-02-2009, 14:43   #7
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Thanks All, you have given me a bit more confidence. Big decision imminent.

Actually, decision already made! I love this boat - just a matter of relating the price to the work that needs to be done. Appreciate your advice.
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Old 02-03-2009, 17:59   #8
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I agree that blisting on older fiberglass boats is basicly a non issue. More fear is put into buyers about this than anything else, IMO.
Unless there is delamination of the hull, its just mainly a cosmotic issue.
They can be fixed, or not depending on what you want to do. Many so called experts have written about it over the years, and like a lot of things in life you get what you pay for. Free information is usually worthless.
If you go to a yard and ask them, well they of course will say it needs repair at some astronomical cost cause everyone knows boats have lots of mony right? They want your money too.

There are some boats like the 1970's valiants that used bad resins that are probably not a good boat unless you want to spend very large sums of money to repair.
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Old 02-03-2009, 18:46   #9
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blisters & Osmosis

this article from my website may be of interest.

OSMOSIS Mythology( a highly simplified explanation )

If I knew what an osmosis test was I could be doing a lot more business as I get asked for it all the time. Dock talkers often use "blisters" and "osmosis" as interchangeable terms however, there are different types, causes and degrees of blisters and using the word "osmosis" just confuses the issue. I am often asked if I can perform an osmosis test to which my response is " What's an osmosis test ?". This response is met with a blank look as the people asking the question really don't know what they are asking.
This is one of the reasons I dislike the word "osmosis" as applied to boats, it has become a generic term to describe all types of blisters and moisture content in fiberglass hulls cored and uncored. Strictly speaking for osmosis to occur you need fluid on both sides of a membrane. If you have this situation on a boat, you have more problems than a few blisters. What you are really encountering is simply water soaking into a porous material. Polyester, epoxy and vinylester resins are not waterproof, they are hygroscopic ie. They can absorb and retain water! (less so with epoxy and vinylester). I have heard many convoluted definitions of osmosis in attemps to justify the use of the word but what we really have is simply a process of absorption.

OSMOSIS: The tendency of fluid substances, if separated by a porous, membrane to filter through it and become equally diffused.

So lets forget about the semantics and get to the issue................
There are many of causes of blistering, To list a few ....... trapped moisture during moulding, undercured resin, overcured resin, aerated resin, incorrect timing of subsequent layers, absorbent fillers, voids, trapped moisture in core materials, stale catalyst, emulsion bound mat, dusty mould, hygroscopic dust, cold mould, inadequately mixed resin, uncontrolled temperature and humidity levels during moulding process, uncontrolled temperature and humidity of raw materials in shipping, orthophtalic (cheap) resins. OK .... enough ! If I really thought about it I am sure I could come up with more but lets just say this, it is an extremely complex issue and "osmosis" just does not cover it. all you need to know is about blisters.

If you insist on calling osmosis then it follows that all fiberglass boats have it !

NO VOIDS = NO BLISTERS (maybe) : There are dozens of reasons for voids in a laminate (some chemical) and they can range from tiny champagne size bubbles to several square feet although most are less than 1/2" in diameter. The average laminate may be 8-15 layers of various types of glass fabric made up of millions of miles of microscopically thin glass strands wetted out with resin. It is unreasonable to assume that all voids will be filled whether the wet-out is accomplished by five guys with rollers or one of the admittedly better (but not perfect) vacuum bag processes. All fiberglass layaups have voids, some more than others. The higher the void content, bigger the voids and the more likely and earlier you will see blisters.
A typical 30' , uncored sailboat hull can absorb about 30lbs. of water or roughly 3% maximum weight of the laminate. The glass fibers do not absorb any water and the resin is chemically incapable of absorbing more than 3% so theoretically 3% water content is sturation point of the material (voids excluded). As all polyester reinforced glass fiber and gelcoats are water permeable to some degree, all fiberglass boats left in water long enough will absorb water and probably develop blisters. This is rarely a structural issue (at least in our lifetime) although it can drive the sailboat racers nuts !
If the hull is cored with balsa or the laminate is all chopped strand (read - very cheap boat) then you may have a more serious and expensive issue to deal with as the balsa rots when wet and in the case of chopped strand fiber, the millions of exposed fiber ends wick water like so many straws.

The more common gelcoats are simply pigmented polyester resin of varying levels of quality and these pigments combined with the aeration caused by spraying the product into the mold can make it more permeable than the resin used in the laminate and therefore most blisters appear in the gelcoat. These blisters are usually small (1/8 - 1/4" dia.) and round in shape. While this does have an effect of the sale value of the vessel it is rarely a cause for concern.

Under the gelcoat is usually a "skinout" mat of chopped strand glass fibers that does not contribute much to the strength of the hull but is used primarily to hide the basket weave pattern of the heavier woven fiber which (hopefully) makes up most of the laminate. When water passes through the gelcoat it may wick up the chopped strand fibers of the "skinout" mat. These blisters are usually small, elongated and again not a major concern.

Water that has passed through the gelcoat and skinout mat into the structural laminate may combine with soluble elements that may occur in the voids. These elements could be uncatalysed resins, silane, glycol or salts (not the table variety) or any of the other chemical soup of ingredients that results from the resin curing (or uncured) process. When water combines with these molecules a new, usually larger molecule forms (hydrolysis), thus preventing escape of the fluid since the molecule is now bigger than the microscopic hole it came in through.

HYDROLYSIS:A chemical process by which the oxygen or hydrogen in water combines with an element or some element of a compound to produce a new compound.As these newer, larger molecules multiply deep in the laminate they can get big enough to start to pushing apart the various layers of the laminate as the resin dissolves. This can be a serious issue, it is however relatively rare.

Put on a pair of safety goggles and puncture a few blisters. If they are dry or release a clear fluid, you likely do not have the serious type of blister. If an acidic vinegar like fluid appears this could be the more serious "Hydrolysis" type blister. Be careful as some of these blisters contain fluids under tremendous pressure. If the blister is very large and cannot be punctured with an ice-pick, it is likely very deep in the laminate, in this case drilling a hole for closer inspection may be warranted.

THE CURE? Sorry..... regardless of the chemical companies hype there is no cure. You can only delay the inevitable but a very high percentage of blistered boats will still outlast you. I have surveyed one local boat three times over the last 10 years and each time it was getting another $10k "epoxy bottom job". I refused to survey it a fourth time because a well respected shop was about to do it again using the same improper techniques as the previous three jobs done by others. Whoever buys this 42' motor yacht will be doing it again soon (if there is any laminate left).
Small blisters in the gelcoat may be repaired by sanding, drying and applying an epoxy or vinylester bottom coat. This may help the resale value of your boat. Blisters in the skinout mat can be repaired by the same method but with much more aggressive sanding and perhaps some patching. The larger hydrolysis blisters require complete removal of the gelcoat and probably the skinout mat and perhaps a layer of the laminate (perhaps in local areas or over the entire hull in which case new cloth may be needed). The hull must then be dried to the point where the epoxy or vinylester bottom coat will adhere and washed frequently during the drying process to wash off as much of the hydrolytic fluid as possible. This fluid and water may weep from the hull for weeks, months or even years so washing is crucial to providing a clean surface to ensure the adhesion of the new barrier coating.
This can be a bit of a gamble. Many bottom coats fail because the hull was not dried or washed properly. I have seen boats put under heat lamps for six months before bottom coating and new blisters appeared within a few years. The moisture is so deep in the laminate at a molecular level that it is not easily evacuated. A new system of applying heat under vacuum holds promise for drying hulls but for the most part it's still a gamble.

Give this careful consideration before plunking down $5,000.00 - $10,000.00 - $20,000.00 or more for a bottom job and always ask for a written guarantee (unlikely). Consult an Accredited Marine Surveyor® before spending you're hard earned money.
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Old 04-03-2009, 14:35   #10
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Interesting and educating. Thanks boatpoker.
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Old 04-03-2009, 16:19   #11
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If the blisters are localized, you can certainly do the repair yourself. Or, maybe even leave them be, depending on what your surveyor recommends.

Make SURE you hire the best surveyor available. Get references.

But you can certainly make a lower offer based on the fact that they are there, than you would otherwise.

Particularly in this buyer's market.

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