It is now ten years since I first sailed Mollie. Mollie is a 20 ft centreplate boat which I built from the GRP hull of an old Yeoman keelboat, a few sheets of ply and scavenged odds and ends (Bulletin 154/10) in 1994/95. She had done very well, not costing me more than the price of the odd can of paint and varnish up until last year when I replaced the stainless rigging and had some sails made to my original plan, rather than the re-cut secondhand ones I had used since 1995.

However, the mast, which was made from one given to me, and cut down to the size I needed, seemed to be showing its 40 years or so in use. So I decided that Mollie would get a new mast as a tenth birthday present.

Now the mast I had been using was hollow, with the jib and gaff halyards running inside. I adopted this because that was how the mast was set up originally, and it seemed a good idea to save weight and have as few bits of string as possible rattling around the outside of the mast. I had grown to like this set-up, and so decided to continue it on the new mast. Following my usual strategy, I sat down to think of the easiest way making the object - I'm not a labour-of-love type person.

I managed to get a really good clear length of Douglas fir, which seemed so expensive I was thinking that I would need to mortgage my house and sell my kidneys. (Every time I cut off a bit I mentally calculated how much it cost!) I had a hand-held circular saw, a belt sander and a jack-plane as my main tools, and this is my simple method for making a hollow wooden mast.

Method

1. Cut blank to length, width and depth, taking care to cut a square end, and allow for planing, calculating how much you would have saved if only the wood yard had sold you the correct length!

2. Cut a piece of card/paper to the size of the cross section of the blank, and mark the diagonals. Mark a circle the size of the diameter of the mast. Mark a line across each of the corners just touching the circle so it forms an isosceles triangle. You can do this by trial and error, or exercise your fading maths skills. This will allow you to measure off and mark the lines for your 45 deg. cuts you will make with the circular saw. It is possible to do all this by calculation if you have masochistic tendencies. Mark a square on the diagonal which gives the wall thickness you want at the corners. I went for (a minimum of) 25% of the diameter, which means that on a 9cm diameter mast there is about a 3 cm square hollow inside. You can now take the distance from the outer edge to make your cuts, marking a line across the mast halves about 30cm from each end.

3. Mark the lines on the mast blank using a marking gauge if you have one, or marking lots of points the right distance from the edge and joining them up with a straight edge. Using the same method, mark a centre-line down each face of the blank. You will now have three lines on two faces and two on two faces. Set up the blank in a position where you can cut it safely – two 'Workmate' benches is a good way – and set the saw to cut 45 degrees. Set the saw gate to cut the correct distance defined by the outer lines. Take care – hand-held saws can wander.

4. Cut two opposite corners off. You will see that we cannot simply turn around and cut off the other two corners as the saw-gate would have to slide along a 45 deg. cut. However, fear not, there is a simple solution.

5. Set the saw back to 90 deg. and cut your valuable lump of wood neatly in half down the centreline. (It is a good idea to then use the halves reversed end-to-end to reduce the possibility of warping if you have any doubts about the timber.)

6. Use the new cut as the edge for the saw gate, set the saw at 45 deg. and cut down the remaining two lines.

7. The next bit is where care is really needed, as we are going to cut out a triangle from each half which will form a square when the two halves are joined. Note that the ends are solid when the mast is assembled, hence the lines 30cm from each end, marked in Step 2. (This distance might be affected by the height of the bolt through your tabernacle if you use one.)

8. Set the blade cut depth to the same measurement as the side of your original outer square, and set to 45deg. Cut carefully from 30cm line to 30cm line.

9. Use a good chisel to cut ends free. You should be able to remove a triangular strip of wood from each mast half. Clean up the inside and faces. (When sanding I suggest gloves, as fir has a habit of providing nasty splinters!)

10. Cut the holes for any fittings. As I have a VHF aerial and masthead light, I ran B&Q plastic conduit down the inside also to take the wires. Another time saver is to put in a line before assembling which will allow you to pull the halyards through. If you have a router, I imagine you can put it to good use putting in any channels for the wires etc.

11. Glue mast halves together making sure that there is support along the length. I used resorcinol glue as I was putting it together when the temperature was low, and the weather damp. Had it been warm I would have used epoxy, which is more sensitive to temperature and humidity. Not having lots of clamps, I used lots of jubilee clips to apply the pressure.

12. Finally, finish shaping with a jack plane and belt sander, and varnish.

13. Good luck!

Dave Jennings writes:

I have concerns about making the weakest point of the mast occur at the same point as the glue line as this is a potential area of failure unless the joint is perfect. My preference would be to make the cut-out so that the square cut-out has its side perpendicular to the glue line (moved round 45 degrees from Tim's cut-out). This gives a much larger glueing surface and can be achieved with a series of circular saw cuts at 90 degrees to the blank removing the wood in between the cuts with a chisel. Of course the cut-out then does not need to be square and could be circular.