MacGregorSailors.com

Al, in an attempt to educate myself about blistering, I have now poked about on the web. In a nutshell, I came up with the general feeling that Catigale and RussMT may be right on the money in advising that one just leave the blistering alone. The web seems to caution that, in most cases one stands a much better chance of making things worse by trying to repair blisters oneself (or even if a 'professional' does it). It seems encouraging that MacGregor uses fiberglass mat for hull manufacture (rather than small individual fibers in a paste). And I have always been pleased that Macs do not use sandwich-type hull layup (ie. hulls cored with materials such as balsa or foam).

It is always a bit dicey to quote web sources - especially in a piecemeal fashion as I have below; but I was certainly snapped awake by the following:

1) from an apparent surveyor
http://www.yachtsurvey.com/BlisterRepairFail.htm
“The bottom line to blister repairs is that there are far too many people in the business who don't know what they're doing. They apparently are not aware that for the repair to be successful, they must eliminate the defects that caused the blisters in the first place. Yet it is not possible to determine all of the factors that cause blistering, especially the cause of water getting into the laminate. The buzzword is "osmosis," as if permeability of coatings is the only means of water saturation" [ie. water permeating the hull structure]. "The reality is that we can identify a half-dozen ways that water can get into a laminate that have nothing to do with exterior coatings. So even if there were a totally effective, non-permeable coating, it would not solve the problem, for you can't prevent the absorption of water from the interior of the hull, or around through hull fittings and so on.”

2) http://www.fiberglassatlanta.com/docume ... 20Boat.pdf
“Blistering involves only the gel coat and surface mat in 99% of the cases. This is due to the fact that the structural fabrics, such as roving, get saturated" [ie. saturated with resin during original hull manufavture] "better. Its also because the water is less likely to penetrate beyond the mat and, even if it does, woven fabrics do not have the weak gel coat factor and are much too strong to allow whatever pressure may develop within a void to cause a separation. The incidence of blisters occurring within structural laminates is extremely small.”

Kittiwake
ps. don't forget to tell us what you find as you investigate the source of the wet interior

Kitiwake : In a nutshell, I came up with the general feeling that Catigale and RussMT may be right on the money in advising that one just leave the blistering alone.

One may enjoy melted ice cream....

Doupirate wrote:

Kitiwake : In a nutshell, I came up with the general feeling that Catigale and RussMT may be right on the money in advising that one just leave the blistering alone.

One may enjoy melted ice cream....

Heh Heh, fair comment.

But with regard to 'melted ice cream', check also the 'surveyor' thread,
http://www.yachtsurvey.com/BlisterFail2.htm
On this latter thread they comment, with regard to specific examples of unsuccessful blister repair jobs,
"But what held my attention was that these bottom coatings had turned to mush. Virtually all of the materials applied to the bottom were as soft as day-old paint. Moreover, the stuff was saturated with water and styrene, which has a strong vinegar-like smell. Pick any spot on the bottom and prick it with a sharp knife and this styrene based fluid would start to seep out. Anywhere."
and
" ... the situation has become so severe that we can only counsel against buying a boat with a botched blister repair job."

Kittiwake

I applied my Interprotec preventive barrier by myself, while following all Interlux instructions to the letter. So I know for sure the job was done right.

My hull bottom is now steel hard and I WILL NEVER HAVE BLISTERS ON MY BOAT

I never had a scratch deeper than the first Interprotec white layer. Every fall,I touch-up the scratches with epoxy and antifouling. Normal hull maintenance.

But believe me, epoxy is no gelcoat. It really is steel hard.

Good mechanical and osmosis protection. I also protected my daggerboard, rudders and the inner of the daggerboard well, up to the water line. Not expensive at all, but the sanding job prior to application is a man's job. The coal mask, googles and paper suit are no luxury.

You must protect the environment from the very fine dust sanding gelcoat generates. It is carried by the breeze and lands on cars, houses walls or other boats.

I've yet to get a definitive answer why it is NECESSARY to repair blisters. Especially tiny ones that show no signs of increasing size.

Now one could make a case for speed reduction (we own Macs, not J boats) with added friction. Cosmetically it freaks some people out at resale time.

As stated above, repairing them risks even more problems, especially if they are not major.

Blisters are the same as cancer: they do not go away. They can only increase as the anthropy of the universe increases . Aggressive treatment is the only way....

If you wait, your hull will become spongy, heavy. Actually, with osmosis, your hull is dissolving. That's what it is.

Dry-up the matt, fix it and keep it. By the way, the drying time, the key, is about 4 months.

You will never resell it...!

IMHO, prevention is the only way to go.

"Aft berth liner and blister job on 26X
by Doupirate » Tue Jan 03, 2012 11:39 am
I applied my Interprotec preventive barrier by myself, while following all Interlux instructions to the letter. So I know for sure the job was done right.
My hull bottom is now steel hard ..."

I must admit, I like the idea of an extra layer of good fiberglass on the bottom ... and I have made a note of the Interprotect product for future reference. Also I am guessing that you are correct: the best job might well be done by a careful and thoughtful owner. My more immediate concern however is the strictly cosmetic one of wanting to touch up the scrapes on my blue hull (which show up really well as white-on-blue!). Proving that I have no life, I am toying seriously with the idea of trying to match the blue with some WM gel coat repair (NOT to the whole hull) ... tried first in a small and not-too-conspicuous place.

Kittiwake

Kitiwake:
I must admit, I like the idea of an extra layer of good fiberglass on the bottom

No it is no fiberglass. No fiber at all. It is pure epoxy with something like micro-shingles in it....

For your concern about your blue hull gelcoat, here is what you should know.

The blue Macs are not gelcoat blue. They are thin blue paint layer above white gelcoat. No big deal, except the number of compound polishing is limited to two. After, the white underneath starts to show white dots.

Blue is real nice. But it is dark. In the summer sun, it becomes hot, real hotter than white, and becomes soft. You must get these blue cloth socks that go above the fenders. White fenders will become blueish after as little as two warm days.

For your scratches, do not work on your boat for now. Work on your trailer. It has to be modified to prevent lots of trouble when sitting the boat in it. An impossible mission to me as I performed it only three times in three years !! What the f....!!!!

Doupirate wrote:Blisters are the same as cancer: they do not go away. They can only increase as the anthropy of the universe increases . Aggressive treatment is the only way....

Perhaps. They arrived the first year. Have not gotten bigger or more numerous since. I doubt they will ever increase as the glass has reached its saturation point and the wax seals the remaining pores. In retrospect, if I had waxed the bottom the first year, I doubt I'd ever have blisters.

If you wait, your hull will become spongy, heavy. Actually, with osmosis, your hull is dissolving. That's what it is.

In my view, this is one of those boat buying fears. It's glass. GLASS. Glass does not absorb water. It is inherently resistant to water. It's glass. Put water in a glass it does not get spongy or absorb anything. Honestly, this is one of those issues I have trouble with as I believe it's overblown. In some instances blisters can be an issue, but not wholesale.

Dry-up the matt, fix it and keep it. By the way, the drying time, the key, is about 4 months.

Agreed about the drying time. I live in the desert and things dry very fast here. However, I'm contemplating fixing it for the reason of good adhesion of bottom paint. I don't want it flaking off at the blisters.

You will never resell it...!

No offense, but this is a scare tactic. It depends on the market. Here, there are few boats and fewer experts on boats. I sold my runabout in 2 days sight unseen for more than I paid for it. Resale in a flooded market, you are probably correct. Marine surveyors (like home inspectors) get paid to find problems. You feel ripped off if you pay $500 and he says, "looks good". So they come up with these "problems" to justify their fees. Sorry, that's my opinion.

IMHO, prevention is the only way to go.

Never hurts. But my Hunter34 NEVER had barrier coating in 20 years of being in the sea. She was pulled each year, bottom paint sanded and recoated. No blisters. It was also SALT water which is denser.
Again, no argument with prevention.

Russ, it's not the water that's the problem, per se, but that being said, fiberglass *does* absorb water. And when the water infiltrates the fiberglass it produces acids that degrade the fiberglass and eventually ruins the strength of the structure.

For anyone investigating blistering and repairing blistering I strongly recommend this book:

http://www.amazon.com/Osmosis-Glassfibe ... 236&sr=1-1

A preview may be found here:

http://books.google.com/books?id=QzZZcs ... &q&f=false

Doupirate I take your point about the "fiberglass" vs "epoxy" distinction.

I must admit to being disappointed with the 'tenderness' of the blue coating, and you have explained it nicely. Ironically, I had ordered a white hull; but it came in blue, which is too fancy for my Spartan nature ... and I was not inclined to wait for a replacement.
I have to admit that my hull scrapes derive from genuine interaction with docks rather than the trailer. I have since developed a theory that one should practice with someone else's MacGregor before buying one's own.
Useful input from all: thank you.

Kittiwake

Delamination. Water permiation causes delamination over time if left in the water. But that aside,blisters create drag. And, these boats are not fast in the first place. Bottom coating creates drag to the point of about 1 Kt. on a Mac. Also, Mac uses the cheapest gelcoat available. My first 6 months with a coated bottom and I ended up with hundreds of blisters. Some people get lucky. Some gel is better than others. There is not set rule.
capncarp,
99

Never noticed any blisters on mine apart from the mold blemishes and never waxed for the first year but do coat with Lanolin grease each year before launching which possibly protects it but certainly makes it really easy to clean ( hot wash) any animals that do build up but the only place they seem to stick is where I have wiped it off on a bar etc and even then easy clean still.

Arent you guys worried about the FG absorbing the water from the ballast tank on the thousands of boats that are slipped ?

Blister repair is a giant FUD.....

No, because the dissolved material would go out the way the water went in. Negligible.

Not the same as with a semi-permeable membrane, the gelcoat, that causes osmosis and pressure building.

Nevertheless, I make sure I dry-up my tank every winter, force-venting it with a fan.

Better too safe than sorry.