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The Sailboat Diaries: Fiberglass-By-Numbers

Posted May 30, 2017 12:54 PM by HUSH

Summer is almost here which means sailing is kicking into high gear. Alas, my 1970 Matilda and I are still on the hard, at least for the next couple months while I finish her refitting. A cold winter made it unbearable to do much for her between late November to March.

For new readers and old readers alike, at the end of last boating season I bought a sailboat. She’s pushing 50 years old and although she’s structurally sound, there are many, many things, both mechanical and cosmetic, that I’d like to refurbish before she is rechristened and relaunched.

Autumn ended just a little early last year and I didn’t get around to my transom reinforcement. Instead that had to wait until early April. I elected to use System Three Epoxy Resin along with fiberglass roving to reinforce the area. Colloidal silica was added as resin filler to give a more peanut butter-like consistency, so it could be spread into the crack and not run as much on the inclined wall.

To begin I measured out and cut five sections of fiberglass roving and I labelled them 1-4 in order of application, which is also smallest to largest. Before applying the epoxy, I held these pieces dry against the repair area and numbered where I thought they should fit. Because it was a warm day and the epoxy sets in about 20 minutes, I needed to work efficiently and this ‘fiberglass-by-numbers’ technique seemed appropriate.

The first piece of roving was thoroughly wetted and wedged into the crack with the help of a putty knife. I did my best to prepare the area inside the crack by passing some sandpaper through it first. Subsequent glass cloth sections had their outline painted with epoxy and then were wetted on top with more epoxy.

Something I didn’t anticipate was the glass cloth roving conforming to the subtle rise in the transom wall where an original metal plate is fiberglassed in. In the middle of this process I cut a new third layer out of the cloth and made some cuts to the middle of the cloth the help with this. By this time the cloth layers were starting to tack and I had to put the fourth layer on immediately. (When the epoxy mixed up in the mixing container starts to smoke, you know you don’t have much time left!) The result is a final layer of fiberglass that doesn’t conform to the wall as well as the two layers before it (as the first layer is underneath the crack). Laminate reinforcement is messy work but is an essential skill for many DIY boat owners.

In the original transom reinforcement thread from last year, there was some discussion about adding an additional metal or wood bracket to this section. I was initially in favor of this idea, but had to abandon it for a few reasons. First, the largest bracket I could fit was 29 inches long, due to the working space of the lazarette and space availability of the transom wall. I also needed space to the left of this repair area to mount components for my bilge system (the next project). Lastly, I also bought the sailor DIY Bible, AKA Don Casey’s Complete Illustrated Sailboat Maintenance Manual. After reading the sections on epoxy laminates, I was comfortable moving forward without the brace.

From the beginning this was a peace of mind fix and not a critical repair. During the first few times that I fire up the outboard on the water I’ll watch this area for flexing and will also inspect throughout the season for evidence of increased cracking.

Ultimately this was just the first checkmark in a long list of projects, both ongoing and impending. Updates on my progress and questions for the community will be faster going forward.

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Guru

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#1

Re: The Sailboat Diaries: Fiberglass-By-Numbers

05/31/2017 1:57 AM

Did 'Don Casey's Complete Illustrated Sailboat Maintenance Manual' really recommend dealing with a crack in a critical area by first passing a piece of sandpaper through the crack and then using a putty knife to wedge a piece of resin wetted roving into the crack?

Really and truly?

Perhaps this 'sailor DIY bible' (much like other bibles) is best not always taken literally.

.

Cracks are best repaired by first grinding until untracked material is reached. Shoving roving into a crack is not a good way to proceed.

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#2
In reply to #1

Re: The Sailboat Diaries: Fiberglass-By-Numbers

05/31/2017 9:05 AM

No, there was nothing as specific as that in the book. Rather it made me comfortable moving forward without a brace after reading more on the history and strength of fiberglass, especially fiberglass repairs.

A grinder was never going to fit into this work area and if it could, I wouldn't be able to use it and also see what I was doing. For prep work, considerable low grit sanding occurred, and a rasp was used to file down the edges along the crack. Once the gel coat was removed from this area the resin is better able to impregnate the original laminates.

Are you saying I should have removed the area/material outlined in by the crack? Unfortunately that's not possible.

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#3
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Re: The Sailboat Diaries: Fiberglass-By-Numbers

05/31/2017 1:22 PM

If you can fit a putty knife in the Crack, then you can fit a dremel in the Crack.

Small hairline surface-only cracks are one thing. Cracks big enough to push a putty knife in are quite another.

Decent reliable fiberglass repairs of cracks that go deeper than the surface, requires removal of material until solid uncracked material is reached.

By shoving roving into a crack you are leaving a stress riser, creating a lever point, putting the remaining old material under additional stress, and supplying new material that will not be good in tension as it was wadded up to push into the crack.

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