Saturday, 25 May 2019

Getting Ready For Interior Fibreglass

While I was waiting for the reworked fillets to fully cure I decided to invest some time in making patterns for the fibreglass cloth panels which would soon be required for the interior of the bottom of the hull.

There are nine 'bays' in the bottom of the boat. Each requires a layer of fibreglass cloth to be applied port and starboard, overlapping up the sides and across the keelson and over each other to maximise the strength of the hull.

First I measured each bay and made a scale drawing of the pattern for one half of each bay, including the overlaps.

Here is the drawing for bay 3, which lies between bulkhead 2 and floor 3.

Then I marked out the patterns full size on sheet paper. I used thin paper so that it would conform easily to the shape of the hull.

I cut out all the patterns and test fitted them in the hull, as here.

The next step will be to use the patterns to cut 'glass cloth panels. I will most likely do this inside, where I can place two or three tables together for the work surface. There isn't sufficient room in the workshop.

Right now I'm enjoying a short break after finishing the fillets, although it has now occurred to me that I might have to add more fillets along the join of the keelson and the centre board case if I decide to run an overlap of cloth up onto the side of the case. That would be tedious, to say the least!

Sanding Fillets | Vale Of Tears Revisited

In the previous post I said that I was not happy with the quality of my workmanship, and that some of the fillets would need rework. There was no question about it. If the boat was to be strong and attractive, more sanding misery was required.

So, I spent some time deciding which fillets needed to be improved and made a work list.

The first thing I did was to tape out the keelson fillets, like this.

I should have done this in the first place, to achieve broad and neat fillets.

Then I set about reworking all the items on my list. By now I had become relatively expert at filleting and it only took three days to carry out all the remedial activity.

Another six days of dressing and sanding followed before I declared myself content with the size, strength and appearance of all the fillets.

At last, the agony was at an end. It felt like I had been working on these fillets for months but when I checked my log I found that the entire exercise had taken just over five weeks. I don't think that is a bad investment of time, given the importance of strong joints.

The next step is applying fibreglass to the interior bottom panels of the hull. It will be a very welcome change!

Sanding Fillets | This Vale of Tears

I have to admit that I became very despondent when faced with the task of sanding the fillets to a smooth curve. It was no surprise. I knew it was coming but I was still downhearted at the prospect of spending hours and hours scratching away at rock hard epoxy.

I made a half hearted attempt to begin sanding, using a piece of pipe insulation as a sanding block, and it barely scratched the surface. A crisis of motivation had set in.

I had read on one builder's blog that he was so demotivated by the prospect of sanding that he only managed one hour's work in the four weeks following completion of the fillets. I could easily empathise.

So I did nothing for a couple of days. While pondering how to find the energy to get going again it struck me that professional finishers must face this challenge every day, and they certainly don't do it by hand!

So I did some Googling and I discovered carbide burrs. A carbide burr is an industrial abrasive head mounted on an arbour for use in stationary or hand held grinding tools, for the purpose of deburring, shaping and finishing hard materials. A diamond cut burr will shape stainless steel and titanium, so it will handle epoxy with no difficulty.

I decided that a ball shaped burr would be best, and purchased one with a 16mm diameter - the largest I could find. Here it is.

A trial run with it fitted in my little DIY Bosch cordless drill worked quite well, but it quickly depleted the battery and the drill did not have the necessary grunt to drive the burr at the high speed which it needs to be effective.

My cordless professional  DeWalt drill is too big and heavy for use inside the boat, but luckily I had a third, small corded drill languishing in a drawer from many years ago. It is an ancient Bosch, so old it even has a chuck key!  Here it is, with the burr fitted.

It is powerful (400W) but is small enough and light enough to use inside tight spaces, and it proved ideal for dressing the fillets. It took four days to do the entire boat. The poor old Bosch got a bit tired after several hours of continuous use, but it held out.

I had removed the sharp and lumpy surface of the fillets, but they would still need to be sanded to a smooth finish - especially where they are visible. But I was happy to have otherwise saved a huge amount of work.

This is where I made my second discovery. I called the burr vendor to ask how long the burr will last, and in conversation he suggested that I consider SpiraBands. I had never heard of them, but I had a look and they seemed to be just what I needed to finish the fillets.

Again, they are industrial abrasives. They are cloth-backed sandpaper cylinders which slide onto a rubber holder mounted on an arbour for stationary or hand held use - ideal for use in an electric drill. They come in various lengths and diameters, although the choice of grits is quite limited - mostly coarse. I purchased a selection of sizes - 60, 30, 20, 15 and 10mm diameters. 

This is what they look like.

So then I went to work with the SpiraBands to smooth the fillets. Like the burr, they worked really well. I soon found that these abrasives work best on epoxy at low to medium speed, so I used my little variable speed Bosch cordless drill. The abrasives are much more controllable at low speed. As previously mentioned the battery only lasted ten or fifteen minutes, so I purchased two spares and by keeping them  fully charged at all times I was able to work without interruption.

In practice I found that I used all the diameters, depending on the size and angle of the fillet. The big 60mm was ideal for the wide and shallow chine fillet, which is why I purchased that size.

The final stage was to hand finish the fillets with 80 grit aluminium oxide sandpaper, which I now buy in 50 metre rolls because I use so much of it. That way it works out really inexpensive.

The pipe insulation made quite a good sanding block for the chines but all the other fillets required much narrower blocks. I found that thick cardboard folded into double and triple thicknesses made ideal sanding blocks, offering a solid edge but being slightly flexible they could adapt to the curve of the fillets. A cork block was useful too.

All this sanding took what seemed like an eternity, and I have to tell you that it was mostly abject misery.

Truly, I thought, we have entered the vale of tears.

Other builders told me to keep going, and that once the fillets and fibreglass are completed the build gets back to being fun again.

So I kept the faith and soldiered on until I had sanded the very last fillet. This whole process took two weeks.

Theoretically I should have been ecstatic, marking the occasion with a celebratory glass of something cold, but alas I was only too well aware of an uncomfortable truth … I was not happy with the quality of some of my fillets.

The bottom fillets in the stern compartment were not big enough, and needed to be beefed up quite a lot. They were the first ones I made, and I was over optimistic about how much epoxy would be required.

The same applied to the fillets in what I would normally call the stem of the boat, at the very front. Not big enough or strong enough to take serious punishment if something hit the bow.

And all the keelson fillets were not good enough. They were too thin and patchy, and quite frankly not neat enough!

And here and there around the boat were incomplete or scruffy bits of fillet, which needed remedial work.

There was no doubt that I had a lot more work to do to make the fillets fit for purpose, and that we were still very much stuck in this vale of tears …

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!

Wednesday, 27 March 2019

Support Beams

I meant to add a note to the previous post about the need for support when leaning into the hull to work on the boat. Copying other builders I fixed blocks to the tops of the cradle arms and clamped support beams to them, like this.

Without these it would be difficult if not impossible to work safely and comfortably when leaning into the boat. As it is I could only just reach the centreline when wiring in the bulkheads and floors. You need long arms for this build!

On the same subject it is essential to have the keel supported properly at the stern, to stop the boat tipping backwards. Here is the support block which I made.

Next phase is tack welding everything together with epoxy. Should be fun!