Saturday 27 April 2019

Removing Stitches | Filleting & Mud Pies

When the tack welds were fully cured and I trusted them to hold the hull together, I removed the wire stitches. I snipped each stitch and most came out with a quick pull of the pliers, but a dozen or so were trapped firmly in the epoxy weld.

I used a heat gun to heat the wire and soften the surrounding epoxy and they all came out with no trouble at all. It only took twenty seconds or so of 250°C heat to warm them up sufficiently.

This is the heat gun, which I purchased half-price last year in a DIY store closing down sale specifically for this purpose.

It has six settings, from 60° to 600°C. What a bargain!

So now the fun began … I had not really been looking forward to this phase of the build. Applying the fillets looked like a bit of a messy trial-and-error exercise, and there was no doubt that sanding them smooth for the fibreglass cloth would be a real challenge.

This is the tack welded hull without its stitches.

I was delighted that nothing flew apart when I removed the wire restraints, and indeed it felt stiff and strong. I put a piece of scrap 18mm ply across the four middle floors to stand on when working in the boat, and it felt rock solid. So far, so good.

I got hold of some filleting tools. I made the one on the right to make the very wide and relatively shallow fillet on the midships chine.

In practice I only used these two tools, plus the two flexible plastic scrapers to clean off the 'flash' from the sides of the fillets.

I used a 50/50 blend of micro fibres and wood flour to thicken the epoxy resin.

I found that I needed to add enough fillet blend to the epoxy until it became just thick enough to stand up on the mixing stick, and no more. That means adding the blend in small increments as it nears the required viscosity.

Any thicker than this, and the fillet stays where you want it to, but it turns out with a surface like roughcast concrete.

Any thinner and it quickly sags and has to be scraped off before it starts to set.

For dispensing the mix I used medium sized freezer bags. I twisted the open end up tight and held it in place with a plastic clip, snipped off the end, and went to work.

I found that quantities of about 150 or 225 millilitres were ideal for me, giving time to apply and shape the fillet before the mix started to go off.

So … after five consecutive days of applying mud pies to the hull with gradually increasing success, the fillets were done!

Here is the boat with its not-very-pretty fillets.

Note that I found it necessary to remove part of the reinforcement cut-out in bulkhead 7 to apply the chine fillets. I would otherwise have glued the waste part of this bulkhead into the fillet, which would not have been useful!

Every single one of these fillets will require extensive sanding. Even my best ones have the texture of sharkskin when fully cured, and they are as hard as concrete.

I think the next stage of the build is going to require imagination and fortitude in large quantities ...

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