PS Advisor February 1, 1998 Issue

PS Advisor 02/01/98

Blister Problem
Last fall’s haulout for stripping and painting the bottom of my 1969 Pearson 35 lasted over seven months. By the end of the process, all identifiable blisters had been cut out, filled and painted over, with one exception. That one, 6" above the keel, continued to “weep” despite being heated with a 150-watt heat lamp for many hours. When the boat was put back into the water, that one spot had not been sealed. My question is, where did that water come from and what will happen while the boat is in the water?

In this part of the country, cruising boats stay in the water until their bottoms need to be repainted, and with good bottom paint that might not be for two or three years. In this time, will the boat absorb a lot of water and become noticeably heavier? When next I haul the boat out, what should be done to it to repair this blister?

H. Martin Weingartner
Nashville, Tennessee

The first thing we would have done prior to relaunching would have been to hire a good surveyor experienced in the use of a moisture meter. He would have given you some idea of the relative wetness of the hull laminate, especially in the area around the large blister.

Secondly, he might have been able to give you some idea as to why the hull blistered in the first place. There are a number of causes, and one cure doesn’t necessarily fit all causes.

In a worst case scenario, the gelcoat must be “peeled” by an experienced yard (this has replaced shotblasting, which is far more damaging to the underlying laminate). Then the laminate must be dried. Catalytic heaters apparently do a better job of driving out moisture than space heaters inside low-humidity tents. Then the hull should be sprayed with vinylester resin and chopped fibers, followed by fairing compounds and resin, and lastly, an epoxy barrier coat such as Interprotect 1000/2000 and bottom paint.

Best results are achieved if the resins are post cured by heating the hull to, say, 120°. This is especially important if the cause of the blisters was uncured resin (perhaps caused by insufficient catalyst). Naturally this is different than if the blisters were caused by a chemical reaction of moisture to the sizing used to hold chopped strand mat together, which brings us back to the different causes issue. Where did the water come from? Hard to say, maybe the ocean, maybe the bilge, maybe a combination of the two. Possibly even a leaky water tank, but we doubt it. Certainly leaving the boat in the water will only cause it to absorb more and make drying it that much more difficult later.

Too bad your yard couldn’t solve the mystery of the one weeping blister before relaunching. Yes, the boat may continue to absorb moisture, grow heavier and the laminate weaker. We hate to see you haul out sooner than planned, but we wouldn’t wait three years and probably not even two. We'd haul again, retain the most knowledgeable surveyor and go from there.

Radar Mounts
Do you have any information on the value and survivability of the radar mounts (a damped pendulum arrangement probably) that keep the antenna relatively horizontal during heeling?

John Morse
Springfield, Ohio

Because radar transmits a relatively flat horizontal beam, heeling of the boat causes a gradual loss of the images you want, i.e., other boats on the surface. When the boat is heeled, the radar will end up scanning the sky and the water near the boat, not the horizon.

Therefore, various companies have developed a number of different solutions, including gimbaled mounts for the backstay and mast, and radar “masts” that typically mount at the stern, and which have tilting platforms. Some of the latter can be manually adjusted to compensate for the boat’s heel, others have pneumatic or other fancier and more expensive mechanisms.

The Questus is probably the best known gimbaled system, though Performance Marine now has a less expensive alternative. Edson and others make a variety of radar masts. The above-mentioned brands can be found in the West Marine catalog.

We have not heard reports of inferior workmanship or defective materials regarding these products. They seem to be well made, but we’ll try to do a complete report on them in the not too distant future.

How valuable they are depends, we guess, to some extent on how you use your boat. If you’re a coastal sailor who is mainly worried about having radar in fog, we’re not sure the gimbal mount is worth it. You may be motoring in the calm fog air anyway, thereby staying fairly level. If on the other hand you’re a blue-water passagemaker who wants radar working at all times, while sailing heeled over night and day, a gimbal mount would make sense.

Comments (0)

Be the first to comment on this post using the section below.

New to Practical Sailor?
Register for Free!

Already Registered?
Log In