Went to check out a boat, it's a 1990 Macgregor 26s, not the power sailor, but a regular sailboat with a swing keel. Boat bottom has several bald spots like these where the gelcoat or paint got scratched off. Boat will be kept in a saltwater slip, are these immediate concerns, okay to address them in the coming winter?
Is this boat bottom okay?
- Thread starter newsailor72
- Start date
The photos are a little hard to see as they are so small.
In general, if you can individual glass strands in the resin, it needs to be sealed up. The first step is to prep the exposed areas and fair with an epoxy fairing compound that is suitable for underwater use. After that is may be necessary to seal the bottom with an epoxy barrier coat and then an antifouling paint. These jobs are easily DIY jobs.
In general, if you can individual glass strands in the resin, it needs to be sealed up. The first step is to prep the exposed areas and fair with an epoxy fairing compound that is suitable for underwater use. After that is may be necessary to seal the bottom with an epoxy barrier coat and then an antifouling paint. These jobs are easily DIY jobs.
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,872
Yes!
The raw fiberglass opens up the possibility of water intrusion. Gelcoat or epoxy barrier coating provides a barrier to reduce the opportunity for osmotic flow into the structural layers of the hull.
Repair before sitting the boat in salt water for the season.
Could you get lucky, sure. Maybe. Do you want to do that to you newly purchased boat?
Your boat your choice.
It looks like the swing keel trunk? Maybe from pulling on/off a trailer?
Gelcoat provides no structural component to, or waterproofing of, the underlying glass, so the fact that it is missing is inconsequential.
However, one of the pictures looks like the area was abraded well into the glass. The pictures don't have great perspective, so this might not be the case.
As far as what to do: If these areas are due to transferring it on/off a trailer, then try to fix on the trailer what is causing the problem.
If the boat is hauled regularly and you can't fix the trailer problem, then do nothing. Maybe recoat the area with some epoxy and paint, but this will probably wear off too if it is due to trailering.
If the boat is to be kept in the water most of the time, then covering these spots with some epoxy or epoxy barrier coat might be useful, but if the rest of the bottom isn't coated already, it isn't very useful to coat these areas.
If those areas really are gouged deeper into the glass, then definitely filling them with some thickened resin will be useful.
To answer your immediate question, you can wait until winter to address them, but I wouldn't leave it in salt water without antifouling paint, and I wouldn't antifoul over them before fixing them - so you better at least coat them with epoxy now and antifoul over it.
Mark
Gelcoat provides no structural component to, or waterproofing of, the underlying glass, so the fact that it is missing is inconsequential.
However, one of the pictures looks like the area was abraded well into the glass. The pictures don't have great perspective, so this might not be the case.
As far as what to do: If these areas are due to transferring it on/off a trailer, then try to fix on the trailer what is causing the problem.
If the boat is hauled regularly and you can't fix the trailer problem, then do nothing. Maybe recoat the area with some epoxy and paint, but this will probably wear off too if it is due to trailering.
If the boat is to be kept in the water most of the time, then covering these spots with some epoxy or epoxy barrier coat might be useful, but if the rest of the bottom isn't coated already, it isn't very useful to coat these areas.
If those areas really are gouged deeper into the glass, then definitely filling them with some thickened resin will be useful.
To answer your immediate question, you can wait until winter to address them, but I wouldn't leave it in salt water without antifouling paint, and I wouldn't antifoul over them before fixing them - so you better at least coat them with epoxy now and antifoul over it.
Mark
John and Higgs have given good advice. Though this is not an immediate structural problem, it WILL result in problems. The only questions are, how bad will it get and how long will it take?
What you are looking at (judging from the pictures) is a really simple repair if you do it now. If you wait a season, it might not get worse, but it certainly won't get any better. Do it while it is out of the water. It should only take a few days, and most of that will be just waiting for things to cure.
Since you'll have to remove metal components from the affected areas, inspect them carefully for corrosion. I have heard/read that water can work its way through the laminate and create accelerated corrosion in nearby metal. I have not personally seen this, but since you have to remove those parts anyway, best to take a minute to inspect.
What you are looking at (judging from the pictures) is a really simple repair if you do it now. If you wait a season, it might not get worse, but it certainly won't get any better. Do it while it is out of the water. It should only take a few days, and most of that will be just waiting for things to cure.
Since you'll have to remove metal components from the affected areas, inspect them carefully for corrosion. I have heard/read that water can work its way through the laminate and create accelerated corrosion in nearby metal. I have not personally seen this, but since you have to remove those parts anyway, best to take a minute to inspect.
There seems to be a misconception that gelcoat protects underlying fiberglass from water and osmosis. This is not the case. Gelcoat is just thickened resin, and is as permeable to water as the underlying resin (a bit more, in fact). There is no difference between a gelcoat covered hull and one without gelcoat. Removing the gelcoat does not make the underlying glass any more likely to absorb water. An area of hull with gelcoat removed will not have a higher probability of water intrusion than the entire rest of the hull covered in gelcoat.
But in the OP's case, if he wants to leave it in a dock in saltwater, he will need to antifoul the bottom. If he is antifouling the bottom, then he should fair the worn spots before antifouling.
Mark
But in the OP's case, if he wants to leave it in a dock in saltwater, he will need to antifoul the bottom. If he is antifouling the bottom, then he should fair the worn spots before antifouling.
Mark
One caveat to this statement. If raw glass fibers are exposed it is possible for water to enter the laminate due to poor bonding of the resin to the glass fibers. Water can wick up along the fiber into the laminate.
This will work if the filler is 407 or 410 filler, however, the microballoon filler can leave small pinholes when sanded smooth. Depending on the repair this may or may not become an issue. Denser fillers will be more difficult to sand smooth. A better choice is Interlux WaterTite or TotalBoat TotalFair. These fairing compounds can be used underwater, have a long pot life than West System and are very easy to sand to a fair finish.
That depends on the level of fouling in your area. If you are new to having a boat in salt water, the amount and quickness of fouling might surprise you.
Mark
My answer is yes.
The strength of adhesion some critters have on a bottom without antifouling is really high. And they will find your boat in days...
dj
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,872
Look at the bottoms of boats in your LB area that are not used every month. The critters will attach themselves and form a colony in less time than you can imagine.
If the local docks and piers are covered with muscles, they are there just waiting to find a new boat bottom.
If the local docks and piers are covered with muscles, they are there just waiting to find a new boat bottom.
I'm in Redondo Beach
I would say yes, you should put on bottom paint. And, you will still need regular hull cleaning.
The sentiment isn't wrong, but I want to raise a few points that are important.
First, we aren't just talking about gelcoat. The OP pretty clearly has some exposed fibers. That is the real issue, here, as Dave rightly points out.
But, while it's true that gelcoat isn't perfect at preventing water ingress, that doesn’t mean damage to the gelcoat doesn’t matter. It does accelerate water ingress, which gelcoat otherwise slows. And, in this case, exposed fibers dramatically accelerate that process and change the character of the failure.
It is not true that gelcoat is more permeable. I would be interested to know where that idea comes from, as it's not something I have heard before. It might come from the (correct) observation that osmotic blisters often form beneath intact gelcoat. It is true that gelcoat is not impermeable, but it is a better barrier than the underlying layup resin.
Gelcoat is typically an isophthalic polyester or vinylester resin, thickened with thixotropic agents (like fumed silica) and heavily pigmented. It’s engineered specifically for:
- UV resistance
- Surface hardness
- Water resistance
For example, water vapor transmission rates (WVTR) are consistently lower for properly cured gelcoat than for underlying resin laminates. Exposed fiberglass (especially unresinated strands or dry spots) is orders of magnitude more permeable, due to:
- Capillary action (wicking)
- Lack of complete resin encapsulation
- Fiber microstructure, which holds water between filaments
- The raw laminate behind it
- Exposed or damaged glass
- Even the same resin without the additives that help seal and harden gelcoat
Read on, only to go into the weeds on this:
- Gelcoats are typically isophthalic polyester or vinylester, not orthophthalic.
- Compared to the cheaper orthophthalic resins often used in layup:
- Isophthalic resins have lower water absorption and better hydrolytic stability
- Vinylester resins are even better—they resist osmotic blistering far more effectively
- Gelcoat contains fumed silica, pigments, and sometimes waxes or surface sealants.
- These reduce porosity and improve film formation at the microscopic level.
- Pigments help by absorbing/reflecting UV, which otherwise breaks down resins and increases porosity over time. (Not so relevant on the bottom, but good to know.)
About bottom paint: I would like to say that cleaning once a month would be fine, but as other have pointed out - probably not. Maybe if you cleaned more frequently, at least during certain times of year?
If you don't want to paint the entire bottom, you could just paint the words, "No marine life" on the bottom to let them know your boat is off limits. It's kind of hard to make out in this small photo, but that's the strategy this boat used:
If you don't want to paint the entire bottom, you could just paint the words, "No marine life" on the bottom to let them know your boat is off limits. It's kind of hard to make out in this small photo, but that's the strategy this boat used: