Friday 24 July 2020

Seatback Blocking | Fitting & Levelling

With the transom skirt permanently installed and the upper stringers now fixed in place, it was time to install the blocking in the seatback tops. The blocking will receive hardware fittings later in the build.

The pieces of blocking had long since cured and had been made ready for shaping. It remained to bevel them to fit tightly between the sheerclamp and the upper stringer in each seatback.

To achieve this I made a cardboard pattern for the top face of each piece of blocking. Here are the patterns for the two pieces which will carry spinnaker sheet blocks on the starboard side, either side of the seatback frame support at bulkhead 7.

There is a distinct curve to the inside and outside edges of these pieces. It is very slight but it has to be taken into account when shaping the blocking. If they were fitted with straight edges the stringers would be deformed.

The angles are taken off the sheerclamp and upper stringer with a bevel gauge, and marked up on the blocking. The bevels are then made on the sides of the blocking pieces using a variety of tools. Wood rasps and saw rasps were especially useful.

Here are the two pieces of spinnaker blocking test fitted on the port seatback.

I had no idea where the spinnaker blocks would end up being fitted, so I asked for ideas on the PocketShip forum.

The labels show where two builders told me to put it. One said 26 inches from the cabin wall, and the other said 55 inches from the stern. You can see that there is a big difference!

I guess the simple answer is that it doesn't matter too much where it goes ... and it will be some time yet before we have to worry about that.

When I had obtained a good fit on all the pieces of blocking I glued them in place, held with temporary screws.

I fitted them with about 5mm raised above the seatback, to allow for flattening and levelling.

Here the port spinnaker blocking is being levelled off.

I am using planes and chisels to rough them out at this stage.

This is the blocking at the stern on the starboard side being levelled and flattened out.

I am using a Japanese  saw rasp to flatten out the blocking, and the orbital sander to finish it off with P80 grit.

Here are the spinnaker blocking pieces on the port side, levelled and finished.

And here they are on the starboard side.

You can see the holes where temporary screws held them in place during installation.

It is very important that the rearmost piece of blocking at the stern is absolutely flat, both across the seat back and fore and aft.

This is because it will be bored to receive the 25mm steel tube for the boom gallows, and a stanchion support fitting will be fitted on top of the seatback to hold the tube in place.

Each tube must be perfectly perpendicular to the seatback, and in line with its counterpart on the opposite side of the boat.

So I spent a lot of time fussing here, to make sure it was as flat as I could make it.

The result was this.

The bubble in the level is exactly in the middle, as it should be. Hooray!

Finally, as a last check that everything was as good as it could be, I laid my longest level across the boat at the stern. Like this.

To my great satisfaction (not to mention relief), the bubble was again right where it should be. In the middle of the glass!

What a result!

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