A Small Boat Mast


John Atkin

Originally Published in The Rudder, April, 1946



IN THE process of developing our new Atkinized fast sailing dinghy we were faced with the problem of making a strong, light and inexpensive mast. The main idea was to have the dinghy fast, practical and simple, but also to retain all the yachtiness of her older sisters.

Without the facilities of factory equipment, constructing a hollow plywood or aluminum mast is almost impossible. In constructing a grooved mast it is difficult to cut the groove for the luff rope without a power router.



It is evident that the plank method of making a light hollow mast is the most practical for the small boatyard or home workshop. However this construction requires the use of sail track, which is one of the problems we have overcome. Four pounds, which is considerable weight aloft in a small boat, are eliminated by not using a sail track.


Our efforts have produced a light hollow spar of plank construction which has an enclosed luff rope slot, with a smooth varnished finish on the interior of the slot. We have managed to make this spar without the use of special power tools in a comparatively simple and practical manner.


Although I prepared these drawings expressly for our Atkinized dinghy the mast could be used on any small boat. It is entirely feasible to use this spar, with the dimensions altered as required, in a Snipe or similar small boat. (I say this as far as practicability goes, for I am not familiar with the building rules of the Snipe, which possibly outlaw a triangular mast though I cannot imagine why.) As a matter of fact, in Rudder's How to Build Snipe the spar is built up of 1/2 inch stock and is of the same general dimensions.


Triangular masts are not new they have been installed in various yachts during the past thirty years. Harbinger, one of Mr. Gordon Monro's original and famous motor sailers, had a triangular mast.


I am not particularly impressed by elaborate airfoils, teardrop sections and similar forms in connection with small sailing boats. Designing streamlined masts is a highly developed science and, when dealing with such lovely things as 6, 8 or 12 meter racing yachts or a Q class racing yacht, there is little doubt that the shape of the spars is a very important subject. However in a little dinghy which bobbles and gyrates in almost every direction it is not likely that the shape of the mast will be too important. Granted, a well shaped mast will be more satisfactory than some square pole. The triangular is not a particularly bad form and will make up in practicability for any disadvantage it has in shape. Actually its triangular teardrop section presents a wide face to the wind and a taper to the luff.

In selecting the material for the mast look first for a piece of light, straight Sitka spruce. Fir will be satisfactory, but the Sitka spruce is so much better that it is well worth the effort spent in locating it.


I recall that Frank Blake, a fine Irish-Canadian master boat builder who worked for my father some years ago, took nearly half a day selecting a light, straight grained piece of spruce for the mast of Charlie Gould's Suicide boat, Daiquiri. That mast was 26 feet long, 2 3/4 inches in diameter at the foot, parallel sided to within a short distance of the top, and only 1 1/2 inch in diameter at the top. It was made by ripping the spruce into halves which were then hollowed, using templates to assure the desired thickness. The two pieces were glued together and rounded off to shape. This produced a most successful light mast which, my father says, is still being used and has not corroded as a metal spar might, nor come apart from the dampness. Incidentally the spar Frank Blake made weighed only a trifle over 16 pounds.


Sitka spruce, 1 1/8 inch thick, resawn, will measure close to 1/2 inch thick when finished.

I would take the time to fair up the wood and see that it is smooth and free from any slight checks or digs along the edges. You'll be rewarded with a far better spar if these precautions are taken.


If you carefully sand and varnish the interior parts of the mast which form the groove before it is glued up, the result will be a fine smooth surface for the luff rope to run in. Be very careful not to let any varnish get onto the cut out portion which takes the back of the mast. This will interfere with the holding of the glue. In fact, do not varnish any of the interior of the mast except as noted.


I have shown in Figure 1 the general dimensions and sections of the mast. The location of tangs, dimensions of butt to suit step, etc., will have to be taken into consideration when making the masts for various small boats. In fastening the tangs and other fittings do not use screws larger than number 7, 5/8 inch long.


The possibility of having a straight level workbench as long as required seems very slim to me. I have illustrated in Figure 4 a suggested manner of setting up the bench upon which to make the mast. Be sure that this bench is straight, for the grooved side of the mast is to be a perfectly straight line.


The mast will be set up with the groove side down. I would let the sides run past the actual back of the mast the entire length and remove that excess wood after it is glued up.

Two solid pieces of Sitka spruce at the foot and head of the mast can be installed after unclamping. Slip them up the required distance, as shown, with plenty of waterproof glue such as Casco, Weldwood, etc., and then clamp until the glue is set. Nodes or bulkheads have a tendency to weaken a mast and consequently should not be installed.


A power saw, with dado, will eliminate a great deal of work in making the mast. However, if the spruce is cut to approximate dimensions at the mill doing the resawing, there will be no further need for power tools. I have eliminated any back-cuts and as many bevels as practical. It will require more time to make the cut, which takes the back of the mast, with a rabbet plane and chisel; but it is a straight line and therefore should not present any difficulties.


Cutting the taper at the head of the mast will be a little more work. The sides and front piece of the mast have to be tapered. The front piece, as shown in section A-A of Figure 1, has to be tapered so that it will come down into the vee section, otherwise the angle of the vee will increase. The taper, which is all on the forward side (as shown in Figure 1) begins approximately 6 feet 1 1/2 inches from the top. There is a slight amount of side taper starting 3 feet 5 inches from the top. This is shown on the after face of the spar in Figure 1. This taper is made by planing 3/8 inch from each of the side pieces at the top, decreasing to nothing 3 feet 5 inches from the top.


In using the wooden clamps it will be necessary to make up some long wedge shaped pieces. These should be about 9 inches long and driven in against each other, as I have shown in Figure 2. Mark a center on each clamp and stretch a line from end to end of the mast after it has been set up in a preliminary manner. Then, after sighting along this line, tap each wedge as required to straighten the mast.


There will be a saving in the number of boat builder's clamps required if you make a number of jib shaped pieces approximately 11 inches long to fit against the mast as shown in Figures 3 and 4. These pieces will distribute the pressure from the clamp swivel plates over a larger area so that fewer clamps will be required, and they will also prevent the clamps from slipping.


There will have to be three or four short lengths of 1 by 3 inch stock nailed over the top of the spar after it has been glued, clamped and ready to set. These will hold it down and prevent any shepherd's crooks from sneaking in. When the exterior of the mast is finished, planed and sanded smooth, give it three or four coats of a good grade of spar varnish.


The time and care spent in making each part and in setting up the preliminary work will result in a superior mast because it will go together more easily and be much stronger.


The spar will weigh only 25 pounds. This compares favorably with other spars about which I have read and which I have seen. An aluminum mast of the same length and diameter will weigh 26 pounds complete with fittings. I have not been able to find a definite figure giving the weight of a plywood mast of the same dimensions, but feel safe in saying the triangular mast will not weigh more.