Accelerated Drying Schedule

Hello, Long time reader, first time poster ...
I upgraded from a Dinghy to a Keel Boat a month ago. The 1980 Catalina 30 was delivered recently and now sitting on jackstands for the winter. The hull has a few baseball sized blisters that I'm looking to fix (the rest of the boat is in good shape). My focus of this repair is just on the big blisters and not worrying about doing a whole bottom job. My question is related to the drying portion of the blister repair.

From my research, a key component of fixing a blister is a dry hull. I'm in the midwest and its basically humid all year around and I don't want to miss a major portion of the sailing season next year either trying to find the ideal conditions.

My idea is to get everything that could contain moisture out of the cabin, completely seal off the boat, run a heater inside the cabin, and then run a vacuum pump around either the entire bottom or just around the blister repair site. This would happen after the blisters are ground out and washed. This would be a rinse and repeat procedure for several weekends.

My expectation is that the heated inside will cause any moisture to perspire to the outside of the hull and the vacuum pump will increase the speed of that process and concentrate the efforts on a few points.

Is this idea too far-fetched from reality to make a difference in the speed of drying or do you think there is some merit. I'm open to suggestions on omitting (or improving) parts of the process that sounds like a waste of time or that could help. Or any general feedback would be useful.

Thanks in advance!!

 

The short answer is you're wasting your time.

I can't see the blisters, so there's no way for me to know exactly what's going on, but here's the issue.

Typical osmotic blistering requires the laminate to absorb water, as the water breaks down some of the soluble substances the blisters form, and they form at different rates. The large blisters you can see are just that, they're the ones you can currently see, there are many thousands more sites forming, or already formed that you can't see on the surface. Going through the work of repairing a few large ones leaves many thousands lurking unseen and ready to erupt.

Any unseen and unrepaired blister will continue the blister forming process, if you can dry the laminate out, which can be difficult to do, it will slow the process, but it will continue at an unknown rate as soon as moisture levels rise again.

Repairing a few large blisters isn’t going to slow or stop the blistering, it will just make those small spots look better, nothing more, so consider it cosmetic and short term. To repair these blisters don’t worry about drying the hull, it won’t make a difference, just grind them out, dry the spot, and do the repair.

It is possible that these few blisters formed for some other reason, paint failing, poorly done repair, bad fairing job, etc, which means the hull may not be blistering.

 

Have you seen this?

http://www.hotvac.com/default.aspx

They do a similar thing commercially.

 

Thanks for the insight. Heikki, I'm glad to hear that my thought process isn't too far off knowing that a company out there is doing the same thing. Ondarvr, I may just stick to that advice that perfect is the enemy of good. I've included a few photos for S's & G's. I suspect it's Osmotic blistering from my limited knowledge. When I popped those pimples, I had to dig in at least 1/4" for 10 - 15 spots, they were under some serious pressure, and some nasty brown fluid shot out. I ended up having to use a heat gun to unfreeze the fluid and then a pocket knife gouge to open them up.

 

Those are big nasty ones.

 

That particular era of Catalina was notorious for massive blistering. You have a few ways to handle this, the first is to treat each as they show up and the second is to get a peeler and have at the skin wholesale. The first approuch seems more economical, though when it's all said and done, you'll spend more time and money this way, simply because you'll be doing this at every haul out for the next ten years. The second approuch gets it all done in one shot and though initially costly, you're through with it when you've sealed her back up.

If electing to go the localized repair route, cut open each blister and let them drain off. Next seal the blister areas with a vacuum bag and put an atmosphere or two on it for a day or two. This will draw out most of the moisture, so the area can be chemically cleaned, then prepped for more resin/fabric.

 

For what it's worth, I purchased a Catalina 38 that had considerable small blistering, plus about a dozen big deep blisters. Unlike you, I was in south Florida in August on asphalt, So it got down to about 90 degrees at 4 am if I was lucky. I did the entire blister repair to the large blisters in about a week. Interestingly, The surface blisters went away before I sanded and repainted the bottom paint, and they have never returned. I attribute the blistering to dock power and continuous AC use for the three years prior to my purchasing it. The blistering appeared in three years on a boat that was free of blisters for 20+ years. The boat has lived on the hook ever since I relaunched it. I ground out the big ones, Washed and dried each a couple times a day for 4 days, then repaired with mat patches, ground those back flush, and faired with vinyl ester putty. Eight years on, so far, so good. I have not done any further hull work. Vessels built in the winter months seem to be more prone to blistering than those built during the summer. As far as your heater idea goes, that is iffy. Some materials will wick water towards heat, and others, mostly natural animal fibers like wool, have the peculiar property of wicking water away from heat. I don't know which way hulls work. But airflow is unambiguous. Move as much air over the hull as you can.

 

Much obliged for the wisdom passed on thru this forum. PAR, Time and money wise, I'm going to work on the blisters I have and then next season work thru an entire bottom job. The peeler is an expensive tool (I'll def check with my HM to see if he knows of someone with one). The dry ice blasting method may be a win for a one time application given the costs. I've also seen the glass blasting method but I wouldn't be able to get my hands on one.
philSweet, I'm glad to hear that the roids were cured. I'm about 25 years from being able to live down there. Hopefully there is some land that's not underwater. Those surface blisters can go away after the initial grind and clean because the water that caused the blister evaporated and the nasty chemical trace is left over. The chemical trace is supposed to get washed away in the blister repair process (wash and wash and repeat).