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 ...

Monday 8 April 2019

Tack Welding | Securing The Transom

The first tack welding session was more about learning how to do it effectively rather than get a lot done, so I practiced on the joins which are easy to reach - the chines.

I started off using a large food freezer bag as a dispenser. It worked OK but dispensed a lot of epoxy in one go, and it was starting to go off by the time I had finished smoothing out the tack welds with a filleting tool.

So I downsized to a smaller bag, and that worked well too.

Lastly I tried out a piping bag, as used by bakers and the like. This worked really well, being designed for the job and staying quite rigid in use.

I finished the chines and left them to cure.

I had been concerned that the build manual is silent on how to secure the transom in place. The assumption is that epoxy fillets and 'glass cloth will do the job, leaving a dry joint between the transom and the hull. I tend to doubt that this approach would suffice, especially in extremis when you really don't want to be wondering if your transom is about to fall out. I decided that a proper glued joint was required.

I therefore backed out the temporary screws holding the transom in place on the port side, filled the gap with thickened epoxy, and tightened up the screws again.

I repeated the process on the starboard side.

Finally I drilled and countersunk pilot holes and screwed the transom firmly in place with 1" 8 gauge silicon bronze wood screws. Three screws in each side and five in each bottom panel. Here is the transom, securely fastened in place.

That transom is not going anywhere!

There then followed several hours of rather tedious tack welding, using the piping bag. It worked well, even when I was leaning over to reach the centre and bottom of the boat. It doesn't hold much epoxy though, and I will need something much larger to do the fillets.

Here are some of the tack welds on the hull, floors and bulkheads.

And here they are in the bow.

The best part of this task was finishing it. I will now leave the boat for a few days to fully cure before I pull out the stitches and start filleting.

More Stitching & Tuning | Gluing Bulkheads & Floors

I mentioned in my previous post that after fitting the bulkheads and floors I had a gap between bulkhead 1 and the bottom panels which I was not entirely happy about. There was also a gap between bulkhead 2 and the bottom panels, but to a lesser extent.

I experimented with a ratchet strap around the hull  and blocks of wood to pull the bottom panels upwards to the bulkheads, but it quickly became apparent that something would break if I went down that route. So that tactic was immediately abandoned!

Advice on the PocketShip Forum was to simply put in more wire stitches. There are clearly not enough holes for stitches in the panels as supplied. So that is what I did.

The gap below bulkhead 2 closed nicely with an additional three stitches in each side. This is what it looked like after tuning.

I added a lot more stitches to bulkhead 1 (four or five on each side) and that tightened things up as far as possible, leaving a small gap that will be easily taken up by the epoxy welds and fillets. Here it is after tuning.

So far, so good …

Then in readiness for the tack welding exercise I glued in bulkhead 7 and floor 4. This was a bit fiddly because they were already wired firmly in place and I had to force thickened epoxy into the joints - even trickier while leaning into the boat, hanging on to the centre board case and working one handed …

This is bulkhead 7 glued in place, secured with a temporary screw and a clamp.

And here is floor 4 glued and held in place with a heavy object.

All ready for the tack welding to start the following day!