How to fibreglass a boat

January was way too cold to be in the garage. Most of February was also of that description, so work slowed way down for about a month and a half.

In the latter half of February is when the weather broke and it looked like the daily lows were going to be above 35 degrees Fahrenheit, which is the minimum curing temp of the fast system three epoxy I use.

Prepping the hull

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First step was to cut off the parts of the centerboard trunk that were extruding past the hull bottom, and sand them all flat. I don’t have any pictures of this, but it was pretty straightforward.

In prep for fibreglass being wrapped up into the centerboard trunk, I then had to round over the edges. This I did with a router and a 1/4" round over bit.

After doing this, there were a couple of sections where the centerboard assembly didn’t quite reach the hull bottom - I needed to fill in a couple of divots which I did with thickened epoxy.

Then I went over the hull and smoothed out all of the bumps and epoxy blobs with 80 grit sandpaper. I also applied fillets between all of the hull panels and between the garboard planks and the hull bottom, and then I rounded over all of the hull panels and the edges between transom/bow/planking so that fibreglass would lay down on the curves. My intention is to fibreglass the entire hull, not just the bottom hull and garboard planks.

I didn’t bother to sand the entire hull, as that’ll come later after fibreglass has been applied.

With the hull smooth, there were two more details to be taken care of before fibreglassing could begin - protecting the water tank fill hole and preparing for drips in the centerboard case.

Water tank fill hole

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I wanted to plug the fill hole for the water tank so that epoxy wouldn’t drip down on to the threads and gum them up. This I did with plumbers putty, jamming it up through the hole from below the boat against a flat surface.

Protecting the centerboard trunk

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With wrapping fibreglass over the edge and up into the trunk, I just knew there was going to be lots of epoxy drips. And I wanted to try and mitigate those so that I didn’t have drips running the length of the centerboard case where I couldn’t sand them and indeed they might play havoc with a smoothly rotating centerboard.

So I cut a piece of plastic a little bigger then the size of the centerboard slot itself and then proceeded to tape it into the slot about an inch or so below the edge of it. This would allow enough space for the fibreglass to be wrapped up into the slot before hitting the tape, and hopefully the inevitable epoxy drips would run over the tape and on to the plastic sheeting rather then down the inside of the centerboard slot.

We’ll see if this worked…

Fibreglassing the hull bottom

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I’m using 6 oz fibreglass on the hull bottom and garboard planks.

First step is to measure out fibreglass and trim it so that it drapes a little more then an inch onto the garboard planks and transom.

With that in place, next is to start mixing epoxy.

In general when laminating with epoxy I find that:

• you really need three coats to fully fill the weave, which is what all the fibreglass on this boat will get before initial sanding
• for the initial coat, a squeegee works best for applying the epoxy, but for subsequent coats I find using a foam roller works best. Using a brush is sometimes necessary but I always seem to put on too much (which causes drips) so I try to avoid that.

Water tank fill hole

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Centerboard trunk protection

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How’d I do here? Well…

Fixing a mistake

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I had one section of fibreglass that floated and didn’t attach itself to the hull bottom (and that I didn’t notice in time to fix it) - a round section just aft of the centerboard slot. I didn’t take a photo of it but it’s pretty obvious when this happens, as the fibreglass solidifies with the epoxy in a very light color where it’s not attached to the underlying wood.

The fix is pretty simple - cut out the floating fibreglass, sand the edges to feather the remaining fibreglass, then apply a patch over top.

This will receive three coats of epoxy itself and blend in such that nobody will know it was ever patched.

Fibreglassing the garboard planks

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With three coats of epoxy on the hull bottom, I sanded the lower edge of the bottom fibreglass that had been wrapped onto the garboard planks to smooth it out all around the boat and feather it flat in prep for putting a layer of 6 oz fibreglass on the garboard planks.

I had seen some other builders say they were cutting it awfully close with whether they had enough fibreglass on their roll to do the entire hull and as you can see from the picture above I was short by about a foot. But no big deal, I just cut out small patches to cover the ends of the garboard planks on either side and just like with the patch above once they’re feathered in you’ll never know this is what happened.

I wound up wetting out both the main piece of fibreglass and then immediately putting the patch over and wetting it out as well. This will result in a little bump on the hull that I’ll sand smooth before paint.

I used the same technique on the bow - I overlapped the fibreglass from the port side about 1.5 inches on to the starboard side, wetted it all out, and then immediately went and did the same with the starboard side, overlapping it about 1.5 inches over the bow onto the port side. This provides a double layer of fibreglass over the leading edge of the bow (and indeed I’m thinking of putting one more third layer over the top again once everything’s dry).

You can see in those last pictures that I overlapped the 6 oz fibreglass by about an inch down onto the next hull plank below on both port and starboard, so next steps will be:

• sand smooth and feather in the fibreglass on the middle planks in prep for putting 4 oz fibreglass on the bottom two hull planks on either side
• sand and feather the fibreglass that was wrapped on to the bow and transom for the same reason - eventually they’ll have 4 oz fibreglass applied to them as well
• start building the skegs