When I made the mast for Naiad I took the dimensions of the mast diameter from a number of photos of Shoal Waters. Due to the small size of these pictures and the difficulty in finding a suitable known length on the photos the diameter was a pure guess.

I had already decided to make her mast hollow and the calculations show that you need to increase the diameter of a hollow mast by around 5% compared to a solid mast in order to make up for the reduced strength.

So, I over estimated the mast diameter and then added 5% and rounded to the nearest reasonable dimension and ended up with 100mm or 4". As it happens, this is much bigger than necessary, but as the mast is hollow, it is probably not that much heavier than the mast of Shoal Waters.

For the Northumbria Coble, only 18" shorter than Naiad, the mast diameter is given in the plans and is 70mm or 2 3/4". Increase that by 5% gives 73.5mm and divide that by 2.5 to give the mast strake width to get 29.4 mm. Well, that's close enough to 30mm, so that's what I'll use. A strake of 30mm wide and 15mm thick should result in a spar with a diameter of 75 mm or just under 3". 

I noticed the other day that I have some left over Cedar strips that are a little wider and thicker than these dimensions so just for fun I cut them down to the correct dimensions, cut a suitable notch in one side and glued them together with some ordinary wood glue.

Here is the result. The Jubilee clips were bought for Naiad's mast but were too small. They fit nicely for this spar as you can see.

These strips were cut with the new table saw, unlike Naiad's mast, so the fit is very good.

Once the glue had dried overnight I used a block plane to remove the proud corners. The plane used to belong to my Dad but he generously allowed me to have his tools and other woodworking stuff when he and Mum moved house. Since I can now made the blades really sharp I am able to use the plane as it should be used. Previously I would have used the belt sander to do the job.

One end of the test spar was once and squarest the other was not. Here you can see that end cut square and sanded a little. The joints are very tight and I am very pleased with how it has come out.

This is the piece cut off to level the end. The advantage of a sharp bandsaw blade is being able to make very thin cuts like this.

This is the reverse of the cut off showing the uneven ends.

The diameter across the flats of this test spar is 75.5 mm and very close to the required dimension, so a 30mm x 15mm strake size is going to be perfect for the mast.

When I get to that part, that is. For now, this test piece will be put on a shelf out of the way and will wait until the time when the mast needs to be made.

Time for a cup of tea.