Another traditional approach is to make a spar in two halves just as you may build a solid spar, but to hollow out the internal parts of the halves before assembly. I do not like this method, because the skill required to ensure that the wall thickness is even on both sides is substantial. In addition, and more importantly, the mast is likely to bend in varying conditions of temperature and moisture content - somewhat like a bi-metallic strip.
Some time back, I was asked to make a mast this way for a customer, and here are some pictures in case you are interested in the alternative method.
|One of the test pieces I used for calculation, along with my rough drawings|
|Two halves with saw kerfs finished|
|Adjusting the cut for breadth and depth to account for taper|
Look carefully in the photo above, and you will see how the width and depth of the cuts has been changed to account for taper.
|Solid portion at the tip where halyard sheaves will be placed|
|I terminated the cuts against a circular line so that the hollowed out end would finish in a hemispherical shape|
|Using a chisel to remove the kerfed sections. Demanding work, as a slip or a bit of chop-out due grain reversal would be a disaster.|
|Close-up of chiselling work - lots of adrenalin!|
|Finishing the interior with a convex plane.|
|Mast halves being glued together|
|All spars were marked for eight-siding using this homemade device which automatically adjusts to the taper of the spar|
|Initial cuts were made using a drawknife, but a plane will do it with less risk, even though it is slower.|
|Finishing off drawknife cuts with a plane|
|After planing to an octagonal section, I mark with pencil to more easily guage the cut when planing to a sixteen-sided shape|
|Planed to a sixteen-sided shape. See how the pencil marks help with visualisation. The process then continues to a thirty-two side shape, and then the spar is sanded to a final round|
|Halyard sheaves and shoud and stay chocks at mast head - dry-fitted at this stage|
|The design called for three cleats and a boom shelf. I do not like screwing fittings to a spar as it can cause stress concentration at the screw holes, but these wooden fittings were glued as well, so they added structurally to the mast.|
|Close-up of the cleats I made prior to gluing. These types of fittings can be quickly and easily made from timber found around the workshop, so you don't need to buy plastic ones - wood looks better, is cheaper, and works better.|
|Gaff jaws and boom jaws before being glued to the spars.|