Hull/Gelcoat of C30's Through the Years

[Bob R.]

I've heard numerous times that in the early 80's people started noticing problems with osmotic blistering on their hulls. I have also heard regular mention that C-30's (and other boats) built in the 70's have thicker hulls (gelcoat, both?) than in the 80's, and that these boats don't have the same issues with blistering.I have two questions: 1) What year was the watershed year for the change in thickness (or if this was a gradual process, how did it progess)? 2) Would a 1981 boat have a better/worse potential for blistering problems than a 1978 boat, or did the change happen later in the 80's?I am currently looking at a boat from each of these years. I realize that there are many factors which are different between these years, but this whole hull blistering thing is on my mind today. Assuming all other factors cause these boats to compare evenly, how would the issue of hull construction effect you opinion regarding these two boats? (Okay, so that's 3 questions.)Thanks for any help you can offer.

 

[Dean Bachelor]

a blistered 85

Hey Bob,I suggest you get a sandblaster in there to remove all old bottom paint! I had to redo my bottom, as it had blisters on aprox. 1/2, scattered around but it had them. It was a couple week ordeal but if you have ever done any bodywork its not that bad, hard on the arms and shoulders reaching up though. I also learned thatuntil recently the bottom paint was not waterproof, but now science has developed a true waterproof barier coat.So now mine is better than it was in 85.Any questions E-mail me www.blowinganddrifting@yahoo.comgood luck, Dean

 

[Steve]

Never sandblast Fiberglass

Never Never ever sandblast Fiberglass!!!Never, Ever ever ever ever. Pleeeeeaaaassseeeee!!!!!!!!

 

[Tom]

Steve's correct re: sandblasting

Regarding sandblasting a hull, Steve is correct, never sandblast. Sandblasting creates microfractures in the gelcoat that has been shown to exacerbate a blister problem. There are plenty of places on the web to verify this, plus I have personal experience with my previous sailboat. Yes, I sandblasted an old hull and had an extensive problem with blisters just a couple years later, where none had been seen for the 15 years before.Regarding the C30 hull, I have not heard of a difference between the late 70's to the early 80's in hull thickness or one year being more blister prone compared to the next, within that period of a few years. Basically, if a hull is 20 years old or so, and is blister-free, the odds are that it will remain so, unless something changes or acts upon the hull (Newton's 4th law?). Sandblasting the hull is one example of a change to the hull. A surveyor also once told me that moving a saltwater-kept boat to fresh water has been shown to have an influence on creating blisters (here in the Seattle area we can move a boat from one environment to the other easily). Or possibly the change in environment just worsens a problem that is already there.Unless the blisters extensively cover the hull or are located deep within the laminate, then don't worry about them. Blisters tend to be more of a problem within people's minds than a structural problem in the hull, more cosmetic than anything else. There are other problems with the old C30's that should be considered and checked, such as wet