Q1: what is a good approach to making a repair in the gel coat layer of a Boston Whaler boat?
BACKSTORY
I have a 1978 SPORT 15. There are a couple of minor gouges below the rub rail on the exterior [of the hull) and a couple in the interior [of the hull. The area of each gouge is 0.5-square inch [ that is, a gouge of about 1-inch length and 0.5-inch diameter.
I want to repair but to avoid spending a lot of money. I am not looking for perfection or an exact match in color. The color should be close.
I was thinking of using MarineTex, but do not want [the repair to be] pure white.
Repair Minor Damage to Gel Coat Layer
Re: Repair Minor Damage to Gel Coat Layer
The best method is to purchase a small bottle of color-matched gel coat polyester resin paste from SPECTRUM. This resin has additives that will allow it to cure to hard finish even if exposed to air (which is important because plain polyester laminating resin will not cure to a hard surface if exposed to air). Twenty years ago these little bottles were not particularly expensive ($20), but I see now in 2025 you will be paying $57 for a two-ounce bottle. That seems a bit pricey to me, but--hey--it is a boat. I think I bought one bottle 20-years ago, used a bit of it, and the rest of it dried up. The polyester resin is more or less curing in the can, very slowly, but give it ten years and it will be hard.
I don't know exactly what hue will match your boat, but here is a link to start:
https://spectrumcolor.com/collections/p ... 2356625649
Another approach is to make your own repair resin by adding some tint to a pure-white resin. To produce a color match will require your color vision to have high acuity, to use natural sunlight to illuminate, and to have some skill. You can use artist's acrylic pigments, sold in small tubes at art supply stores, to use as the coloring agent. These also used to be cheap. I don't know what they cost now.
To create a hue close to DESERT TAN buy two colors: Titanium White, and Raw Sienna. The portion of Raw Sienna is very small compared to the white pigment. A good method is to mix a very small amount of Raw Sienna pigment with a larger amount of Titanium White. Mix the two together thoroughly. Then use this new mixed pigment to tint the white gelcoat adding very small amounts until you reach the proper hue.
You probably could add the tint to the white MarineTex--but I have never used Marine-Tex so I don't know how it would react regarding curing.
This pigment can be added to WEST System epoxy resin that has been thickened with fillers to work toward the best match.
I describe this approach in an article from 1998. See
https://continuouswave.com/maintenance-logs/epoxy/
If you use epoxy resin and the repair is exposed to ultraviolet light (sunlight) the hue will shift towards yellow. If the repairs are inconspicuously located, that hue shift may not be important. If you want to avoid all hue shift, use white polyester resin and apply a layer of poly-vinyl alcohol (PVA) so the air cannot reach the curing resin. I have done exactly that and it works fine.
IMPORTANT
On a 1976 SPORT 15 the HULL and the COCKPIT gel coat finishes are actually different colors. The difference is subtle, but it is there.
I don't know exactly what hue will match your boat, but here is a link to start:
https://spectrumcolor.com/collections/p ... 2356625649
Another approach is to make your own repair resin by adding some tint to a pure-white resin. To produce a color match will require your color vision to have high acuity, to use natural sunlight to illuminate, and to have some skill. You can use artist's acrylic pigments, sold in small tubes at art supply stores, to use as the coloring agent. These also used to be cheap. I don't know what they cost now.
To create a hue close to DESERT TAN buy two colors: Titanium White, and Raw Sienna. The portion of Raw Sienna is very small compared to the white pigment. A good method is to mix a very small amount of Raw Sienna pigment with a larger amount of Titanium White. Mix the two together thoroughly. Then use this new mixed pigment to tint the white gelcoat adding very small amounts until you reach the proper hue.
You probably could add the tint to the white MarineTex--but I have never used Marine-Tex so I don't know how it would react regarding curing.
This pigment can be added to WEST System epoxy resin that has been thickened with fillers to work toward the best match.
I describe this approach in an article from 1998. See
https://continuouswave.com/maintenance-logs/epoxy/
If you use epoxy resin and the repair is exposed to ultraviolet light (sunlight) the hue will shift towards yellow. If the repairs are inconspicuously located, that hue shift may not be important. If you want to avoid all hue shift, use white polyester resin and apply a layer of poly-vinyl alcohol (PVA) so the air cannot reach the curing resin. I have done exactly that and it works fine.
IMPORTANT
On a 1976 SPORT 15 the HULL and the COCKPIT gel coat finishes are actually different colors. The difference is subtle, but it is there.