Repairing Hull Damage the Whaler Way

by Taylor Clark


The Whaler Way

Since the hull of a Boston Whaler is constructed in a unique and patented way, the factory has provided special instructions for making repairs to this structure. In this article, Tom Clark and I demonstrate the factory-recommend method to repair damage to a Boston Whaler. Because of the prominent chine line of the hull, the damage shown here is likely to be among the most common above-the-waterline damage situations on a Whaler.

The Damage

Up at Whidbey Island, Washington we have a very funky community float/dock, made from the center float from an old marina. Along the sides of the float every ten feet or so are a pair of big eyebolts that were used to hold the finger piers. I made the mistake of mooring my Montauk there on a night that started quiet but got worse. When the bow fender was forced out, the hull beat itself down upon an eyebolt all night long. Turns out that Whalers have pretty thin skins. You can imagine how sick I felt when I saw the side all scratched up and then realized that two feet of chine were basically gone.


Photo: Close up of hull damage
Damage Detail
Here you can see the worse part, where the damage goes clear through the skin and the foam is exposed. The chopper gun lay-up is pretty clear here, no cloth in sight. The hole is only a few inches high, but it looked huge to me.
Photo Credits: Taylor Clark


Photo: Ruler laid on hull to show damage length
The damage was not confined to just the chine, you can see the scratches and abrasions on the side above the chine where every wave caused the screw eye to dig in. Any one of these scars would ruin your whole day. I started drinking early that morning. Gosh I was low.


Photo: Overview of hull side showing damage
More Damage
Well, now you can see the whole problem. The damage really covers a pretty wide area. Duct tape was used to keep water out and get the boat from the boathouse back to the launch ramp.

What To Do?

I was pretty sure that duct tape is not going to be enough. It looked like I was going to need a highly skilled professional who knows Whalers and is very experienced forming new shapes out of fiberglass. Or I needed Tom W Clark. So now you are going to find out. Is Tom as nice and as knowledgeable as he seems online?

Yes, he is!

Tom and I discussed materials and techniques via e-mail, I got all the supplies together, and one Sunday in early August I towed my boat over to Tom's place in the Ballard neighborhood of Seattle. I had just 14 days until my summer Whaler trip to Desolation Sound, British Columbia. Tom claimed we could do most of it in a day. This was going to be tight.

The Official Instructions

Tom had a copy of the instructions that Whaler used to send with their gel coat repair kits. (These instructions are reproduced in HTML format and are available in a separate article in the Reference section.) Larry Goltz (LHG) had sent them to Tom, and Tom was interested in trying them out. The instructions contained some interesting variations on the usual approach to fiberglass repair, especially adapted for the Whaler Unibond hull. Tom referred to the these instructions regularly if not reverently. By the time we finished, our copy was well worn, and covered with resin.


First I needed Spectrum gel coat, in a shade of Desert Tan to match my model year Whaler. Price: $65 plus shipping for a quart, yikes! And shipping is a lot even though they are in nearby Auburn, Washington. But they're about the only game in town, or the country for that matter. I ordered this ahead. Auburn is a long drive. I also got some black and white gel coat color agents in case I wanted to field adjust the color, which turned out to be unnecessary.

Saturday morning I stopped in at Fiberlay, which happens to be just down the street from Chez Tom's House of Fine Boats. Plus, they're open on Saturday morning. So convenient, Ballard. Fiberlay will ship nationally if you happen to be somewhere other than Ballard. At Fiberlay I picked up the following:

The official Whaler instructions call for a polyester based resin, rather than epoxy, and Tom feels strongly that you ought to use the same material for repairs that was used to build the hull in the first place. In my experience with kayaks, I've always found that good polyester resin sticks just fine to well sanded fiberglass.

Later I needed one more thing, something which is really required for a good job.

Also, here is a list of tools we got together, they are pretty general, and we had them on hand.

Grinding: The Hard Part

We took an angle grinder and used it to remove all the damaged glass. This was really tough because it made things look much worse, the hole just got bigger, and we got covered with itchy fiberglass dust. I'm talking about a pretty large repair here; if you are not through the fiberglass and into the foam this may be too drastic. Note however that we did find that under the scuffs on the gel coat, even though the gel coat appeared to not be cracked, there were serious problems with the fiberglass. After we ground through the gel coat we found broken fibers and a telltale white line that showed the fiberglass was no longer solid, and the damaged section needed to be ground out and repaired.


Photo: Disc grinder working on hull chine damage
Grinder Action
Here is Tom taking the angle grinder to the damage. I could not stand this, I just stood back and took pictures. I think it's easier if it's not your boat. He is trying to remove all the damaged fiberglass and grind the remainder to a feathered edge. We are just getting started with the grinding in this picture. It takes just minutes to do this.


Photo: Close up of damaged area
Flipping the bird
I'm not sure exactly what Tom is trying to say here. He may be showing us the feathered edge he has ground. See on the right side of the main hole, the glass looks pretty solid, while the upper part by his finger still appears to be damaged fiberglass that will have to be removed. I'm pretty sure that the white stuff on Tom's finger is not a controlled substance, although that might have helped me.


Photo: Oblique view of damaged area extending along chine line
The Feathered Edge
Here you can see later in the process that we have taken off a lot more gel coat to expose some hidden cracks, ground out damaged glass and have a feathered knife edge along the old fiberglass. You can also see that we have gouged out some foam behind the old glass, back about 1/2 to 3/4 of an inch

The gouging out of the foam seen in the picture above is accomplished with a little piece of L shaped wire chucked in a drill and run around the edge of the hole. Tom had stainless steel wire (of course) but I think an old coat hanger might do the trick also, although it might be a little thick. A little hand work gets all the loose pieces of foam and glass.

Finally we blew all the dust away with compressed air and cleaned up the repair area with acetone, and masked it off. Then we got ready to make a big mess.

First Layer: Chopped Glass Mash

The special thing about the official Whaler repair instructions is that the fiberglass is applied in two steps so that the whole repair grips both sides of the old glass. That's something I have not seen before in fiberglass repair, usually the patch just goes on the outside. In this case the patch goes on both sides, which is why we were gouging out foam and creating a knife edge above.

First we took some mat and cut it into one inch strips which we pulled into individual fibers as we created a mound of 'chopped glass'. We then catalyzed a 4-6 oz of resin and mixed in the chopped fibers until we had a mash of wet fiberglass gunk. That gets forced back under the knife edge and you fill the hole with it. Two tools work here, one is a brush, and the other would be a 'stick'. Tom might have some special purpose tool for this, but I think a Popsicle stick (tongue depressor) is what you want. We really stuffed and packed the mash back under the edges, then filled the hole and tapped it down with the end of the brush so it was all nice and evenly saturated with no big air bubbles or voids showing. This was the only layer that grabbed the back of the skin so we wanted to make it count.


Photo: Damaged area after first coat of repair
Mash Fills the Hole
Here is the repair after the first layer was applied. The first layer is meant to fill the holes and grab the back of the old glass. Also, if you look carefully at the upper left of the larger ground off area, you should be able to see the previously hidden damage. Look for the telltale white where the fiberglass has been flexed and broken. See if you can find some below the chine also. We decided these do not need to be opened and handled on the first layer, just covered in the second layer.

Second Layer: Mat

The official Whaler repair instructions call for a second layer on the outside of the repair. It's important that after the first layer you are still below the original surface. Otherwise you will just end up sanding off all of your repair. It's going to be OK if you get too much thickness at the edge of the repair, you can grind that off and it won't matter. But make sure that the mash layer is not sitting too high.

So we started the second layer by sanding with 150 grit on a random orbital to try and establish a baseline for the repair. Then we applied a couple of layers of mat. We made sure not to leave voids or air bubbles. The best tool for this is the brush, which is used to tap down on the fibers. Brushing did not work well, although the brush is used to add more resin after dipping it out of the cup. I could tell when I was working too long when the cup began to gel, and the brush started pulling the mat up.


Photo: Damage area after second coat of repair
The Mat Layer
The second layer has been applied, and we have sanded it down and smooth as we try and reestablish the chine line. The pale lavender stuff along the chine is the fiber reinforced putty. You can also see the horizontal lines from the long blocking. Flat repairs are clearly easier than curved or corner repairs.


There's no really easy way to establish the chine line, I'd lost the sharp corner of the chine for a couple of feet. Tom came to the rescue here by making wood blocks that matched the angle of the lower hull to the under side of the chine, covering them with course sand paper. Then we just worked and worked and worked. The long block, which is a large piece of soft wood with sandpaper wrapped around it helps keep the repair level.

We used fiber reinforced putty to fill any low points in the repair. It's pretty easy to mix up with a putty knife, you catalyze it with the same MEK stuff as the resin. But it goes on smoothly with a putty knife, and it's easy to work level. It also hardens pretty quickly. We took quite a few iterations of filling and sanding. Beer comes in handy here, it's hot and thirsty work, and you have to do something while the putty goes off.

High spots turned out to be a real problem when we applied gel coat. We found that any bump created a spot where we might sand through the gel coat. We should have spent more time making sure that it was all evened out. Also, we ended having to fill all those little bubble holes in the old glass with putty, since we wanted a really smooth surface for the gel coat. We discovered that the gel coat does not even out anything, it is too thin.

Gel Coat

I thought we'd never get the boat to look good again, and after the first layer of gel coat, I was sure this was the case. The color match was really good, but the texture of ridges left by the brush took forever to sand out. Don't use a brush.

Photo: Gelcoat being applied with brush
Painting Gel Coat
This is TWC brushing on the gel coat. Well, it's the back of his head anyway. We covered an area from the registration numbers forward to the turn in the smirk, from just below the rub rail down to the sharp edge below the bottom paint line. The idea was to minimize the places where the new and the old gel coat colors touched, and to hide those places in spots that you would not see. This was mid afternoon Sunday August 4th. I don't think Tom expected to be brushing gel coat on Sunday.


Photo: Ridges in finish of new gelcoat
Ridges in the Gel Coat
These are the ridges left by the brush. By the time they get sanded smooth, you run out of gel coat to sand. Don't use a brush. Use a Preval sprayer. The Whaler instructions mention it by name.

Preval Sprayer

The Preval sprayer is a little 6 ounce bottle with a can of compressed gas, an uptake tube and a spay head. It's really pretty easy to use, it spays just like a can of spray paint. You can buy them for $5 at most any good paint store, hardware store, or chandlery. Or so Tom says. Buy two, just in case.

We took the gel coat and thinned it first with acetone, by 25% since we were going to spray. (Note: Spectrum has subsequently suggested that acetone not be used for thinning their gel coat. Instead they recommend using Styrene or Patch-Aid.) Then we added the 'wax' or finishing agent that is included with the gel coat as per Spectrum's instructions. This is required to get a hard finish on the gel coat. Then we catalyzed according the Spectrum instructions. I think it takes about twice what resin does. I recall we mixed about 3-4 ounces up in a separate cup and then poured the mixture into the Preval bottle. The instructions mention that you don't want any uncatalyzed gel coat on the sides of the spray bottle. We found that a little gel coat goes a long way. This entire repair, including two brushed and three sprayed layers of gel coat took a little more than a pint. They only sell quarts.

We sanded it smooth, up to about 220 grit with my random orbital which produces a pretty smooth finish compared to some. Then it was time to blow off the dust, mask off everything and clean well with acetone.

I sprayed in smooth sweeping motions from about 10 to 12 inches. Gel coat does not level well, we saw tiny droplets sticking to the surface and the final texture we got at this stage is something of a sand finish. The spraying was really easier than I expected. It is just like using a regular spray can of paint. If you can spray anything more complicated than tagging in the 'hood you can probably do this.

Wet Sanding

After the gel coat went off, we started wet sanding with 600 wet/dry paper on a block. We were just trying to get through the sand texture and make it smooth. In several places we went too far and sanded through the gel coat. It's really easy to do, and there are only a couple of strokes between a pale greenish tinge and all the way through. When that happened we just let the water dry, sanded with 220 or 300 a little, blew it off, cleaned it up with acetone, and then re-sprayed the affected area again. I ended up spraying perhaps three or four times. It was frustrating.

Final Finish

This is the magic part, were I went from a hole in my boat that is being repaired to a boat that looks like it never had a hole in it. When I succeeded in getting it really smooth with the 600 grit, I switched to 1200 and started making it shiny. I started too soon a couple of times, I really needed to get down and squint at the work to see the areas that were still showing the remains of the sand finish. But the 1200 grit was rewarding.

After the 1200 I buffed the repair out. I had some Maguires #44 on hand, as well as 3M Finesse-It II. I used one, and then the other and then waxed. Finally I repainted my bottom paint and replaced the numbers.


Photo: Finish from sprayed gelcoat
Sprayed Gel coat
Here's the boat after a sprayed layer of gel coat, but before wet sanding. Tom donated the better part of three days to the project (Saturday, Sunday and Tuesday evening) and I did the last few steps at my house without needing him to hold my hand. I think his significant other was a little tired of the whole project. This picture was taken late Tuesday, August 6th.

All done!

With the bottom paint on, the boat honestly looked like new. The only flaw I could see was a little wow in the chine line up forward. The color match is pretty good, the new stuff is slightly darker than the old, but we hid it pretty well. Let me know what you think.

Photo: Restored repair area
All Done
This picture was taken on Friday 8/15. We left Saturday morning for Canada.


Photo: Whaler on trailer hitched to BMW
On the Road
Here's my big rig on Quadra Island, near Campbell River, British Columbia. Proof positive that you can tow a Montauk with a BMW 325. Also proof that my spouse has not yet put the children in the trunk. It's a really small two door.


We actually made it to our vacation with the boat intact and floating. A great time was had by all. And we want to say thank you.


Photo: Young daughter enjoying boating
Maighread on Vacation
Here's a really good reason to have a boat.

Thanks are due to the continuousWave Forum for establishing the kind of community where one member volunteers to help out another when they get into a bind. And of course, thanks are due to Tom W Clark. Tom helped me out for two reasons. One he wanted to try out and document the official Whaler repair instructions, and second, he's just a nice guy. I want to point out that while our last names are the same, and we live in the same town, I am not Tom Clark's brother. If I had a brother, I'd want him to be like Tom, but a little less anal.


A message thread in the Whaler FORUM is available for questions concerning this article and the repair technique demonstrated.

DISCLAIMER: This information is believed to be accurate but there is no guarantee. We do our best!

Copyright © 2002 by Taylor Clark and James W. Hebert. Unauthorized reproduction prohibited!

This is a verified HTML 4.0 document served to you from continuousWave
Last modified:
Author: Taylor Clark
This article first appeared November 15, 2002.