6:00 AM
Update! We could not make our schedule last week so we did not go into the yard. We are scheduled once again, to go on-the-hill June 9th.
Stay tuned.
5/4/2008
12:35 PM
If you are searching for your first used boat you've very likely heard about blisters. Most boaters with in-the-water boats are aware of them. But what are they, how do they form and most importantly, what do you do about them...if anything? I've been involved with 5 surveys since the first of the year and every time a boat was hauled from the water, blisters are the fear from the prospective buyer. You have no need of panicking, however, the issue is easily managed.
My trawler, the Patricia Ann has had a number of tiny blisters on her hull for some years and I've known about it. I've just watched them and evaluated them each time I pulled her out of the water. I've finally decided to tackle the problem. Next Monday, 5/12/2008, she will be pulled from the water to begin the task of removing the existing blisters, drying of her hull and applying a epoxy barrier coat, and finally new bottom paint.
To help you better understand the cause and what to do about it when you are searching for and evaluating your next boat, I'm going to chronicle my project with descriptions and photos. It's my intention that you will have a much better understanding of the issue when your surveyor says, "this boat you wish to buy has blisters".
Technically speaking, blisters are the symptom of a condition that is known as hydrolysis of the laminate. Hydrolysis is the chemical process of decomposition of a material and the addition of water (Webster's). When used in reference to the polyester resin it is the breaking of the bond of the resin. In layman's terms, it's simply the decomposition of uncured resin.
As you will see, not all bottoms with hydrolysis damage have blisters, but all bottoms with blisters have some degree of hydrolysis.
All boats of polyester fiberglass resin design and manufacturer soak up water. I've heard that a boat may soak up to 20% of its original weight in water. What happens is when water penetrates the gelkote, the glass fibers assist by acting as capillarys to transport the water into the laminate. Once inside, the water goes into chemical solution with the resin in the gelkote and laminate.
So how do the blisters form? Blisters form when the flow of water into the laminate is greater than the flow of hydrolysis fluid back out. The acidic solution, under pressure, that is produced by hydrolysis cannot escape back out through the gelcoat and a blister begins to form. Over time, they grow larger and slowly start delaminating the outer layers of laminate. Smaller blisters will combine with others to form larger blisters and the process continues.
One of the most asked questions is "Why do some older boats blister and others do not? What we find is those older gelkotes are porous. Water flowing in is equal to the acidic solution flowing out. The gelkote is much like a sponge. The result may be underlying hydrolysis but no blisters.
So why are blisters and hydrolysis a problem? First, it is unsightly and may slow the boat in the water. But more importantly, if hydrolysis goes unchecked structural delamination can occur. Nothing will scare away a potential buyer faster than blisters.
The affects of hydrolysis on the resin may be quite serious. The hydrolysis process can soften, weaken and remove the resin from the laminate. Strength of the hull is reduced.
You might ask how long might it take for the deterioration to become a structural concern? No one really knows yet; fiberglass boat building has not been around long enough to determine that.
So we now know that any boat with blisters has a hydrolysis problem to some degree; however a boat without blisters may have a problem but doesn't show it. So what can you do to evaluate the hull for hydrolysis?
- Identify the size and frequency of blisters. Blister diameter is often associated with the depth of the blister and thus a rough gauge of the depth of the hydrolysis. Bigger blisters usually mean bigger problems.
- Look for cracks, crazing and pin holes. These may be letting lots of water into the laminate and accelerating hydrolysis.
- Look for sediment piles inside the hull. These typically indicate active hydrolysis, even though there may be no blisters
- Take moisture meter readings both inside and outside.
- Drill or grind into the laminate to determine the extent of laminate damage.
REPAIR OPTIONS:
There are some differences with owners as to the best way to repair blisters and hydrolysis.
Some owners choose to do nothing. Maybe not the best choice, but we all tend to postpone it as long as we think we can get away with it.
On the simplest level, I have simply popped blisters and filled them with epoxy. Some owners have tackled the entire boat blister problem this way and proudly claimed they have solved their problem. Of course, this completely ignores the problem of water continuing to get in to the laminate and causing even more blisters and hydrolysis.
And finally, the most complete repair is the removal of the gel coat and replacing it with a impervious barrier coat.
LAMINATE REPAIRS
Perhaps the only successful method to date of repairing a blistered boat hull is by peeling the gelcoat and any damaged laminate from the boat. Some have tried sandblasting the hull but it's a hit and miss attempt at best requiring a very skilled blaster. The best you can hope for is an uneven, wavey hull when complete.
To begin the repair the boat is hauled, washed and the blocked on stands.
Once the amount of laminate to be removed has been established, the removal process begins. A tool that has become commonly called a Peeler is used. It cuts the gelcoat and laminate off like a hand-held electric planer. It can be adjusted to remove only to the depth of a single coat of bottom paint if need be. The hull is left quite smooth, requiring only minimal sanding and fairing.
The cutting tool is a much cleaner operation in comparison with grinding or sandblasting, both for the boat and the environment.
Once the gel coat and any damaged laminates have been removed, its time to dry out the boat. We now need to remove as much water from the boat's hull as possible before making our repairs. This does not suggest that we will get all of the water out ( I doubt this is possible anyway), but to remove as much as practical.
We've chosen this time of year as this is the dryest season in Florida with the lowest humidity. The boat's hull will be measured initially with a moisture meter to give us some baseline reading. She will then sit for days, weeks, months "draining" water from her hull until we have obtained the lowest moisture readings possible on her hull. She'll be monitored weekly. We've talked about building a tent over her to speed up the drying but the yard says that they have had less than satisfactory results with this method.
After the hull has dried, it will be time to re laminate any areas that were found to have hydrolysed laminates. Woven glass cloth will be used with epoxy.
BARRIER COATING
Following removal of hydrolyzed material, drying of the hull and replacement of glass as necessary, a barrier coat is applied. Epoxy resins are by far the best water-proofing materials to date for boat use. Although they have much higher costs, they have been the preferred resin for many successful repair jobs.
As a barrier coat, six rolled coats will be applied to arrive at a thickness of about .030". Once faired, two coats of anti fouling paint completes the repair.
So there you have it. If you find just the right boat that has some blisters, you now know what they are and how they got there. You also know what options are available to repair.
References:
BLISTERS & LAMINATE HYDROLYSIS by Craig Bumgarner, Updated April 9th, 2003
David Pascoe - http://www.yachtsurvey.com/
Tom Musto - BoatSavers
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