Thursday 13 June 2019

More Work On The Centre Board

We last saw the centre board after it had received its lead ballast back in February, which by the way filled the aperture and its re-machined rebate very nicely.

I next removed the scrap ply backing pad, which held the lead in place during the pour.

You can see how the molten lead charred the ply pad. It bubbled and smoked wonderfully, as it did in the keel.

I used a Bahco scraper to fair both sides to a flat surface.

Next I filled the low spots on both sides with thickened epoxy.

And I then sanded both sides of the ballast to a smooth, flat surface, like this.

Then it was time to shape the edges of the board to a streamlined profile.

First I sprung a strip of thin ply to a fair curve along the trailing edge of the board, taking the line from the drawings. Like this.

Then I used the big Festool sander to shape the board to the profile indicated on the drawings. This was the result.

The leading edge now has a bullet-nosed profile, and the trailing edge has a long taper down to a thin edge. This will slide through the water nicely.

You can see that the edges are protected by epoxy armour which I added to a rebate cut around the edges of the board way back at the beginning of the build. Removal of material during the shaping has revealed the armour, especially on the trailing edge.

With hindsight I don't think the sander was the best choice of tool to do this. The board got pretty hot and I was concerned that the heat might damage the epoxy, but it seemed fine when it had cooled down. If I were to do it again I would use a plane and just finish with the sander.

After shaping I applied fibreglass cloth to both sides of the board. Here is the starboard side with its 'glass, curing.

The drawings say to wrap the cloth around the leading edge at this stage, but mine resolutely refused to stay in place.

So instead I added a strip to the leading edge when I was 'glassing out the bottom of the hull interior, like this.

Prior to this I had recoated the board to fill the weave of the 'glass cloth, and sanded it.

The board is nearly complete. It needs a couple more coats of clear resin and to be sanded to a very fine finish.

The manual says to leave it like this, as do other builders, but I am pretty well decided that I will paint it the same colour as the hull.

Others say that no one will ever see it, but it's actually really easy to see the keel or the board of a boat sailing in clear water. And I think as it is this board is not very pretty!

So it will end up being dark blue.

More Fibreglass On The Bottom Panels

Confident that I now knew how to cut 'glass cloth panels correctly I cut them all out in one session and set them carefully aside to deploy as and when required.

The cloth has to be handled gently and kept from dragging against anything rough which instantly pulls threads. Damaged cloth not only looks unsightly but can be difficult to smooth and wet out nicely.

Installation of the rest of the 'glass panels progressed well and they were all wetted out over the course of four or five days and left to cure.

Here is the starboard panel in bay 7, laid in place and ready for wetting out.

And here is the port panel in bay 2, laid in place and ready for wetting out with clear resin.

The 'glass cloth is actually very compliant provided that I am patient and gentle. It conforms well to the shape of the hull and the fillets and doesn't mind being stretched or pulled slightly to get a good fit.

In bay 1 the steep sides of the bow compartment meant that I had to use a small piece of masking tape to hold it in place while I wetted it out, as here.

And here it is after application of clear resin.

I found that a 4" roller was the ideal tool for wetting out, and a brush was sometimes useful for tamping down the cloth into a fillet or a corner.

I started wetting out in the middle of each panel and worked slowly but firmly out to the edges. On steep sided bays it helps enormously to work up to the top of the panel first. This holds it firmly in place while the rest of the panel is dealt with, otherwise the top just falls down onto the wetted cloth and gets in a right mess.

Brushes are no use whatsoever for applying resin to cloth - they just drag the cloth or pull threads loose.

Here we see several completed bays on the starboard side of the boat.

The very last panel to be installed was the starboard side in the bow compartment of bay 1.

Here it is after wetting out.

And that is almost the end of 'glassing the bottom of the boat! When the bow panels are fully cured I will sand them and add a strip of 'glass tape all the way up the stem and along both chines as required by the build manual, and that will be the end of this activity.

I must say that I have really enjoyed this phase. Well, let's face it - after the endless agony of sanding fillets pretty much anything would be fun!

Next we move on to sanding the 'glass and applying more clear resin to get a perfectly smooth surface, ready for paint. I can't wait to get the sanders out again ...

First Fibreglass On The Bottom Panels

With all the fillets in place it was time to start adding a fibreglass cloth covering to the bottom panels of the hull, for added strength and resilience.

I started with the port side of bay 9 in the stern, between bulkhead 8 and the transom. This will be sealed as a watertight compartment and not visible, so it is a good place to practice in case the outcome is not cosmetically perfect!

I cut 'glass cloth using the pattern I created earlier, and wetted it out. This was the result.

I thought it looked pretty good, so I moved on to the port side of bay 8. That went well too. Here it is, wetted out.

Flushed with success and confidence I then tackled the port side of bay 3, which is a much more complex shape with overlaps onto floor 3  and bulkhead 2 and the adjacent bay. Using the paper pattern to cut the cloth I managed to make an incorrectly shaped panel which did not fit the bay - twice!

I realised that the 'glass cloth was deforming as I cut around the pattern, being much more flexible and pliable than the paper. This was clearly not the right way to do it ...

So, I carefully smoothed out the fabric and placed the pattern on top. Two folding tables placed together provided a suitable work surface.

Then I weighted the pattern down, so that neither the pattern nor the cloth could move. Like this.

I recruited two stuffed chicken doorstops to assist. They are perfect for the job, and they didn't seem to mind helping out …

The trick then is not to cut around the pattern but to mark out the outline of the panel on the cloth itself. I used a marker pen to make a dot every two or three inches about a quarter of an inch from the edge of the pattern. Then I cut along a line inside the dots, knowing that the outcome would be correct even if the cloth was deformed in the process.

It worked perfectly. Here is the end result.

So far, so good!

More Fillets!

I mentioned in a previous post that I thought it would be necessary to overlap the fibreglass covering on the bottom panels of the hull up onto the sides of the centre board case. Advice from others and a closer look at the build manual confirmed that this is indeed a requirement.

When creating the epoxy resin fillets along all the hull panel joints I neglected for some reason to add fillets where the keelson and the centre board case are joined. It is in fact obvious that fillets are required on this join, otherwise it would not be possible to have an overlap of fibreglass cloth from the bottom panels up onto the case itself, since the cloth will only conform to a flat or a curved surface - sharp turns are not possible.

So … more fillets were called for! Readers of previous posts will know how much I enjoyed making and then sanding the hull fillets i.e. not at all, so it was a bit galling to realise there was more to come.

However, by this stage I was fairly proficient at making and shaping fillets, so it was no great hardship to create six more - three on each side of the centre board case.

Here they are, after creation.

And here they are after shaping and sanding.

While I was at it, and having some filleting material left over, I ran a small fillet up the join between the case and bulkhead 7. I will tidy this up later.

The next job is to add fibreglass to the bottom panels. A nice change from sanding fillets!