CONTINUOUSWAVE

Q1: from bare fiberglass or existing gel coat, how can a new, sealed, strong layer be created?

Q2: if a new layer of laminated cloth and epoxy resin is created, then topped with new gel coat, and then with paraffin wax, will an epoxy barrier coat be necessary?

Q3: does the original top layer gel coat resin need to be completely sanded off in order to have a new layer of cloth and resin bond to the hull?

Q4: did Boston Whaler use epoxy as the "binder" for the gel coat?

Q5: did Boston Whaler use polyurethane as the "binder" for the gel coat?

Q6: how thoroughly sanded off do areas of the gel coat which has "yellowed" need to be?

Q7: how are the hull chines restored?

Q8: can 3D-printed molds with some sort of powder-fiberglass filler be used to restore the chines?

BACKSTORY

Since I was very young I have owned a 13-foot Boston Whaler boat that was probably made in c.1967.

I recently moved to Mississippi to work.

I brought the 13-footer with me. I did not have a trailer. I transported the 13-footer in a van. That is a long story.

I am shopping for a trailer.

I want to do maintenance on the 13-footer.

The hull of the c.1966 13-footer is largely good condition. There is good adhesion to the foam and few holes below the waterline, but some spots on the hull are concerning. I want to create a new surface that will last for many decades.

I plan to sand-off the bottom paint and yellowed gel coat, leaving the original white gel coat in place, then apply a fresh layer of fiberglass, barrier coat, and new gel coat. I do not plan to add anti-fouling paint to the bottom.

One area of the hull is "squishy" and likely has delamination. I don't want to tear-up the fiberglass, but I believe my only recourse here is to [cut] out the whole section of fiberglass, dig out all the soaked foam, and then refill with proper two-part polyurethane and re-fiberglass.

This 18-second-long youTube presentation I created shows this area:
https://youtu.be/myQOLaAjdWA






The hull has been patched many times and the hull thickness varies.

I have read the Boston Whaler repair instructions.

This hull has seen so many changes over the years.

I'm curious as to what the best approach is [to repairing the hull].

waterlubber wrote:Q4: did Boston Whaler use epoxy as the "binder" for the gel coat?

Q5: did Boston Whaler use polyurethane as the "binder" for the gel coat?

Neither epoxy or polyurethane were used for the gel coat layer. Boston Whaler boats are laid up using a polyester laminated resin and a polyester gel coat resin.

waterlubber wrote:I plan to sand-off the bottom paint and yellowed gel coat, leaving the original white gel coat in place, then apply a fresh layer of fiberglass, barrier coat, and new gel coat. I do not plan to add anti-fouling paint to the bottom.

Your plan will add considerable weight to the boat, and required enormous work to create a new, faired surface to which gel coat resin can be applied. Then the new gel coat will require a great deal of laborious work to produce a smooth and high-gloss surface. It is unlikely you can get a nice gel coat resin finish. You should consider just making repairs to damaged areas as needed, then fairing the hull and painting it.

This excellent presentation on youTube from TotalBoat demonstrates how the existing gel coat surface can be mostly retained, then eventually painted:

Boston Whaler Crazing Repair
https://www.youtube.com/watch?v=4tZDBOYqdfA&t=90s

I have previously worked on and reglassed large sections of the hull, although largely above the waterline. As it stands during the removal of the bottom paint I took of large sections of the gel coat as well (while I might have taken off fewer sections with a chemical stripper, there were also significant portions of bottom paint directly on underlying fiberglass (!)).

I'm most concerned about the hull delaminating or otherwising allowing seawater into the foam, as the boat is still light enough to be mostly not waterlogged. Visual appearance is less of a concern since all of this will be below the waterline anyway (although fine-scale surface roughness is of course important to minimize parasitic drag on plane and displacing).

Also, I noticed a couple of places where there were thin circular rings, with the same appearance as crazing cracks, radiating from a point. The rings were about a quater inch apart and extended to a radius of at most 2 inches. I'm guessing these were caused by impacts.

Q9: is special treatment of these necessary?

If there are large areas of the hull with no original gel coat intact, I would use epoxy resin to seal the hull bottom and sides. Then build up the lamination of cloth and epoxy resin as necessary following the instructions from Boston Whaler. Sand and fair the entire hull, and paint it.

Using epoxy resin will give you a stronger bond and a better water-tight seal compared to using polyester laminating resin, but epoxy will cost more. But since we are talking about a 13-foot hull, the added cost won’t be unbearable.

This restoration sounds like a lot of work. I suppose there is some sentimental value in the boat, but it sounds like it was neglected for many years in order to degrade to its present condition.

Before you get further into this project, you should weight the bare hull. Compare the present hull weight with the original weight. This hull could be holding a lot of water, and it could be hundreds of pounds overweight.

Have you thought about just getting another 13-footer that is in much better condition?

ASIDE: you might enjoy this CETACEA article:

Grandfather’s Whaler
https://continuouswave.com/whaler/cetac ... age51.html

There is a lot of sentimental value in this [c.1967 Boston Whaler 13-foot hull]. My father bought this boat when I was around ten-years-old, and I've done a lot of restoration and maintenance since. The boat was in far worse condition when we originally got it, but the repairs from back then were not really performed in the best way. BONDO was involved.

Thankfully, the hull weight is quite light. I don't have a scale for it, but I can move it around and lift it up with my father. The hull weight is probably well under 400-lbs and most likely around the 300-lbs or so that the boat should weigh. In the water, the waterline sits below the right-angle cut [chine line] around the very edge of the boat, with engine, gasoline tank, battery, and wood aboard. Planing speed with an Evintude 30-HP is 28-MPH, and perhaps a even higher with favorable [wind and current].

I think epoxy resin and cloth are the best [choices for hull repair materials].

I found the WHALER RADIO podcast with West System; and was very informative.

Q10: Can I mix white pigment into epoxy resin to create a gel coat?

Q11: should I wash off the amine blush and just put regular polyester gel coat resin on top?

Q12: Does epoxy require waxing to cure in humid environments, like polyester resin does?

waterlubber wrote:Q10: Can I mix white pigment into epoxy resin to create a gel coat?

I think you mean you want to created a tinted resin. When epoxy resin is used as the top coat for a boat hull, the resin will be exposed to ultraviolet (UV) radiation from the Sun. Epoxy resin tends to yellow when exposed to UV, so the tinted resin color will shift with age and exposure. You might think, well, the whole hull color will shift together, but that will depend on having a perfectly even exposure.

The tendency for epoxy to color shift somewhat is what tends to prevent it from being used as a final color top coat, although there are some top coat paints that are referred to as "two-part" paints which are color fast. Exactly what those "two-part" paints are made from is unknown to me. I suspect they are some specially formulated resins and hardeners that have been created to prevent color shift from UV-exposure.

You can add pigment to epoxy resin to produce a tinted resin. I haved use acrylic pigments, which you can buy at an art store. Tinting to pure white is the simplest, and a pure white was probably the original gel coat color for your c.1967 hull. Read my article on using epoxy, "The Epoxy Cure". as a repair resin in my MAINTENANCE LOG section of the website.

The Epoxy Cure
Minor Repairs Using Epoxy Resin
Cf.: https://continuouswave.com/maintenance-logs/epoxy/

waterlubber wrote:Q11: should I wash off the amine blush and just put regular polyester gel coat resin on top?

Yes, you should remove the amine blush from any layer of epoxy when you are top-coating that layer with another layer, even if using a second epoxy layer. The only time you don't have to worry about amine blush is when adding a top coat layer to an underlying layer of epoxy that has not cured.

You can also use a material called PEEL-PLY to absorb any excess resin from a layer of laminated cloth, which will also absorb the amine blush. On AMAZON you can buy a 3-feet by 5-feet piece of peel ply for about $20.

https://www.amazon.com/Super-Release-Green-Peel-Ply/dp/B09MZJY7FR/

Peel ply is usually used when doing vacuum bagging, but if it can be retained in place by gravity against the curing resin it should have some efficacy. (I have not tried using Peel-ply.) The concept of Peel-ply is that once the resin cures you can peel off the Peel-ply layer without much difficulty, and the amines will come with the Peel-ply.

Some epoxy resins are sold as being formulated to reduce amine blush.

Overall, washing off the amine blush with soap and detergent is the least expensive way, and for a small boat hull it won't be very difficult.

waterlubber wrote:Q12: Does epoxy require waxing to cure in humid environments, like polyester resin does?

No, epoxy resin cures to full hardness without needing any additives.

The humidity of the air is NOT what really stops polyester resin from curing when exposed to air; it's the air itself.

Wax is mixed into polyester resin that will be curing with an exposure to air so that the wax will rise to the top and form an airtight layer on the top of the resin. This allows the polyester resin to cure to a hard finish while otherwise exposed to air

As mentioned by Jim Watson in the WHALER RADIO podcast, fiberglass laminated boats are typically laid up into a female contact mold. The gel coat layer is the first layer sprayed into the mold. While the gel coat layer is still curing, more laminate and resin is added. The subsequent layers form a primary bond to the still uncured gel coat layer. The gel coat outer surface is against the mold surface, so there is no air present there, and that side of the gel coat resin layer will then cure to full hardness.

Also in molding boats the mold is prepared by being highly polished and waxed, and then typically a release agent will be sprayed into the mold to add additional separation between the mold and the gel coat layer so the finished hull can be pulled or "popped" out of the mold. If the laminated hull does not come easily out of the mold, there will be a big problem in a production boat situation, as the mold is intended to be re-used many times.

The product often used as the release agent is called polyvinyl alcohol. You can buy small quantities of polyvinyl alcohol, typically from paint supply shops that specialize in automotive paints or perhaps from marine fiberglass and polyester resin supply shops.

When you are making a repair in a small area and are using polyester gel coat resin, you can spray polyvinyl alcohol onto the uncured gel coat resin as a way to keep air out and get a hard cure in that small area.

The polyvinyl alcohol will easily wash off once the gel coat resin is cured.

TOP COAT
In the case of the hull under discussion here, my inference is that once all the repairs are done the ENTIRE hull will need to be given a new top coat. For that I would not suggest you spray on a polyester gel coat resin. There are several problems with that approach:

• special air compressor needed to supply lots of air volume
• special spraying gun needed
• experience needed
• protective clothing needed
• enormous odors created
• lots of overspray created
• risk of problems in sags or not-hard cure resulting.

For such an old boat with so many repairs, you will probably be better served by rolling on and brushing a modern top coat paint that is not extremely expensive. Look at TotalBoat WET EDGE TOPSIDE paint. Here is a link to some presentations from TotalBoat on their youTube channel:

https://www.youtube.com/playlist?list=P ... E62vrll9Ma

I recommend you study this very good presentation at

TotalBoat: BOAT PAINTING
https://www.youtube.com/watch?v=99GwPbW ... Ma&index=3

I think TotalBoat can also provide you with more details and recommended specific products and procedures for your particular situation if you contact them directly.

https://www.totalboat.com/

Jim,

Thank you very much for your excellent response. I have had some prior success with using a "Preval sprayer" to apply a top coat, but that was over a smaller, repaired area of the hull. I think this is enough information to form a solid plan and I'll go ahead with the work; with luck I'll be back soon with results.

I'm also redoing an old whaler, so I asked some of the same questions you asked.

My opinions are:

• gelcoat repairs should be fine if you are doing a few small spots. BUT gelcoat is not paint; if you are planning to do more than a few inches, paint (as Jim suggests) will come out better and be a lot less work. But buy good paint, like two-part polyurethane;.
• you can try to add stuff to epoxy to make it more UV safe, but UV will always win;
• do all your repairs first, with epoxy and fiberglass. Then paint the whole thing; a good epoxy primer counts as a barrier coat;
• because Boston Whaler boat are more like surfboards than regular fiberglass boats, most of the general boat repair advice just isn't that useful.

I thought this youTube presentation was helpful:

1971 Boston Whaler 13 total restoration - Part 1
https://youtu.be/RaSL_EZ2Ohk

Kenb wrote:I thought this youTube presentation was helpful:

1971 Boston Whaler 13 total restoration - Part 1
https://youtu.be/RaSL_EZ2Ohk

Wow, that is a very long presentation, with 22-separate segments to watch.

For a bit shorter presentation that really shows in sufficient detail how to recoat the surface of an old Boston Whaler boat whose gel coat is badly cracked and crazed, I suggest this presentation from TotalBoat:

Boston Whaler Crazing Repair
https://www.youtube.com/watch?v=4tZDBOYqdfA

I finished my hull repair work in the Summer of 2025. I have heavily used and trailered the boat since. Below is an update on the repairs I performed and how they stood up. For now, I have only worked below the waterline . I will handle the hull side sides and interior of the boat at a later date.

Overview of repairs:

General work flow steps:

1. removed all bottom paint mechanically using disc sanding with 60 grit;
2. sanded gel coat significantly to rough surface; in some cases, removed gel coat completely and exposed bare fiberglass;
3. sanded out any portions of the fiberglass bottom that were squishy or otherwise clearly delaminated from the underlying foam. These are largely areas of the hull that had been previously repaired with Bondo;and then
4. sanded and then scooped out the chines on the sides of the hull--the squarish joints at the bottom of the freeboard.

For rebuilding the hull, I used US Composites 700 Vinyl Ester Resin, white gelcoat, and surfacing wax. The fiberglass material was chopped strand mat and 3M microspheres.

In general, I would highly recommend going with an unwaxed resin. The ability to lay up a layer at at time, and return the next day, worked extremely well for me as I could complete a layer each day as I got home from work, then let it cure overnight.

I started on the hull sides and the chines, where I built something similar to a concrete form using tongue depressors. The I filled the deepest cavities with a microsphere-based [thickened resin]. These chines had essentially the bare foam exposed, and I used a mix of microspheres and chopped mat to fill and reconstruct the area. I wouldn't recommend this for large repairs, but the scope here was small enough that the actual filled area--and thus thickness of the resin--was limited to less than 1/4-inch.

Due to the high temperatures in Mississippi when I performed the layup I had to significantly reduce [the amount of] catalyst [added to the resin] to get enough working time. I would mix six to eight ounches resin at a time, which was generally the most I could lay out without it setting and becoming unworkable. I had a lot of problmes around the chines at the stern: the mat would not conform unless wetted, and the time it would take to wet, form, and lay up was very tricky to manage. Later a coworker offered advice that he used for carbon fiber layups: use a heat gun to soften the chopped mat "stiffening wax" to pre-form before wetting out.

In some areas of the boat, and particularly the transom, near engine mounts), I used multiple layers of chopped strand mat; usually adding two layers at the beginning and end of an evening lay-up in these locations. This was to replace the significant scoops I had put in the area sanding-out damaged fiberglass, and strengthen this load-bearing area of the structure.

After laying out a full layer of chopped mat I followed it up with a gel-coat; I believe I ended up with two waxed and cured layers and a significant amount of sanding and fairing to produce a smooth surface. This was almost a year ago and I forgot the exact procedure.

Finally after curing the gel-coat I painted the bottom with TotalBoat's epoxy barrier coat primer. I did not add another layer of bottom paint on top of this, as the boat would not be stored in the water.

Ultimately this whole adventure took me a few months; most of this was sanding, sanding, sanding. The work was easily broken into small pieces, however, so it probably took about three weekends and a dozen evenings after work--perhaps not all that much all-in-all. I think the outcome was definitely worth the effort.

Next on my repair agenda are the sides and interior, as I need to rework the seats.

Outcome
It is nearly a year since I performed these repairs and I am very happy with the results. The bottom is as intact and as flawless as it was immediately after repairs, even after a significant amount of trailering, running into sticks in the bayou, and so on.

Additional photographs are found at: https://imgur.com/a/b8cxdB6

[Moderator's note: I changed the orientation of some photographs so that they matched the general view of the others, that is, up was skyward. I wrote captions for the photographs. I gave the three new photographs identifying figure numbers that matched the sequence of earlier illustrations.]