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Fastcast, you may have some good points, but Jeremy SERIOUSLY knows what he's talking about. Defer to the experts. THIS (boat repair/sales/expertise) is his living and he is good at. I have seen him at work on a few beach repairs and its almost miraculous the stuff he can do in almost no time at all. Did you see that 20?? I would still be crying if that happened to my boat.
xanderwess, yes Jeremy appears to do great work, that is probably where is unflexability comes from, professional arrogance). I’ve waited a bit to cool off before responding to SCC (Jeremy’s) request, point by point
Every single 'superior' property of epoxy that you cut and pasted above is moot. THE REST OF THE BOAT IS POLYESTER!
Because the repair material it is not the same as the original does not make the point moot, not by a long shot. I don’t know of any car company that uses Bondo as OEM, but it is a well established repair method for ding repair. HOW is this any different? To say a repair method is not acceptable just because it uses superior materials that differ from OEM is arrogant, ludicrous, pretentious and just plain wrong.
Electrical properties? Does that matter?
Ya it doesn’t.
Resistance to osmosis? Didn't realize that wan an issue here.
Apparently you are not aware of gelcoat blisters. Though not probably part of annacat’s problem, it is still something to be aware of (see below)
Despite most people’s assumptions to the contrary, fiberglass moldings, no matter what resins are used, are not actually totally waterproof. Individual water molecules are so small that they can actually find their way into and ultimately right through the layers of glass and resin forming a boat hull, or GRP pond liner. This in itself is not osmosis, it is simply a minute degree of permeability of the material.
The problems start to occur when the water molecules migrating into and through the GRP encounter other chemicals inside the laminate, primarily water-soluble materials (WSMs) such as the the emulsion binders used to hold the glass mat together before it is molded, or pockets of uncured or only partly cured resins in the molding. The water molecules can then have a chemical reaction with these substances, forming larger molecules of a new chemical, often acidic - which unlike the original small water molecules cannot carry on passing through the GRP. These larger molecules are then trapped. This is the point at which osmosis actually starts. The process of osmosis is the same mechanism by which plants and trees draw water up from the soil to their branches and leaves, and is described in a dictionary as:-
os•mo•sis (oz-mo'sis, os-)
Diffusion of fluid through a semipermeable membrane from a solution with a low solute concentration to a solution with a higher solute concentration until there is an equal concentration of fluid on both sides of the membrane. The tendency of fluids to diffuse in such a manner.
The important parts are that the hull is not waterproof (it is a semi-permeable material), and that osmosis causes a low concentration fluid (water) to pass through the hull to join the higher concentration fluid (the chemical mix formed by the water plus WSM) inside the laminate).
Pressure is thus built up inside the laminate. If this process takes place in a solid part of the laminate, there is usually no problem as the structure is strong enough to contain the pressure. If however it takes place on the boundary of a small air-bubble in the molding, or at a point where layers of GRP are poorly bonded, the resultant new chemical compound or compounds slowly fill up the bubbles or the minute gaps between layers with liquid. Almost all moldings have these air bubbles and small areas of poor bonding, although they should not. Ideally the resin should totally fill the gaps between the glass strands, and every layer should perfectly bond to the next. In practice, however, this is extremely difficult to achieve with conventional molding techniques.
The process of osmosis in GRP is however very slow, unless the molding is appallingly badly made, and no matter how long it remains in water a typical GRP laminate cannot absorb more than about 2-3% of its own weight of water. Surveyors and boatyards (and some brokers, including Yachtsnet) put moisture meters on yachts hulls to check the moisture content, on the basis, often but not always correct, that high moisture levels in the GRP are a precursor to the development of blisters.
If this osmosis (using the term in its correct manner for once) was all that happened, it would be a very minor problem. Even completely saturated with water molecules, a GRP laminate still retains most of its strength, although it does become slightly more flexible. Racers who want stiff hulls with the absolute minimum weight already mostly keep their boats ashore when not sailing, and for any properly built cruising boat 2% or so extra weight and a trace more flexibility in the structure should not be a problem.
Once again, if the air bubble simply filled with this acidic compound, the problem would still be relatively minor. However the nature of the osmosis process is that water molecules keep osmosing through the laminate, and join the chemicals in the bubble, steadily building up hydraulic pressure. Eventually this causes the surface of the molding to blister.
These blisters are the typical sign of what boat-owners usually refer to as ‘osmosis’. When pierced these blisters will give off a small amount of chemical-smelling (usually vinegary) liquid - which is the juice built up inside the pressure-raised blisters. The term ‘blister juice’ is often used. This ‘blister juice’, which is usually acid, can break down the polyester. This breakdown process is known as hydrolysis, and causes a reduction in strength of the laminate. This is however normally very localized, and the molding as a whole will still retain most of its strength despite blistering. Most blisters are in the interface between the gelcoat and the structural laminate, and have very little effect on the hull's overall strength. Only if the blisters are very large, or very deep-seated, are blisters generally a structural problem.
Able to withstand higher pressure? Again, the rest of the boat is polyester. Why does that property matter? You are right, not an issue here, but still a nice property.
Does higher resistance to acid matter? No!
Correct, unless you are concerned about acid rain.
Adhesion? There's not even any problem with adhesion right now.
If there was no problem with adhesion, then the gel coat would not be crumbling off. So the fact that epoxy has better adhesion is a good thing, very un-moot. If I do a repair I want the repair to remain in place.
Does superior bonding matter? No! The boat got a ding, it's not delam.
Correct not a problem in this case, but once again how is superior bonding a bad thing? I think not.
I'll ask again, as you're having a difficult time grasping the concept (FastCat NOTE: not too happy about the attack on my mental acuity, I’m more than willing put my conceptual reasoning to the test, are you?). No cut and paste this time (oops, too late, nothing wrong with cut and paste, I just wanted others to see that epoxy as an alternative to polyester for boat repair is not just a ‘FastCat’ thing, but an ACCEPTABLE practice used by others.
Why would you suggest epoxy for this repair?
Now to the meat and potatoes. I would use epoxy for this repair because:
I don’t like to use gelcoat. I’m not set up for spraying. You have to deal with anaerobic curing or use an additive. Why not just use epoxy.
Epoxy is easy to work with (apply, shape, sand and polish), has superior strength and bonding. It is less brittle so if the repaired spot is hit it will not crack or craze (it might dent a little). I also use epoxy to build up my boats bottom (~1/8”) from the front of the centerboard well to the stern. I feather it in to the hull about 1.5 inches up the side. I’m sure this is NOT a prescribed method of hull maintenance, but it has worked well for me for over a decade and can drag my boat up onto the beach with impunity (I use beach wheels to go beyond that).
AND cost - please - for this size repair hardly an issue, oh wait you prefer MOOT.
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