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Making Wooden Spars


A spar is a general term for any mast, yard, boom, gaff, bowsprit, etc. on a vessel and nowadays they can be made from wide range of materials including wood, metals such as aluminium and the more exotic materials like carbon fibre. However, our focus is on a standard solid mast seen on small and big vessels alike.

The process demonstrated can be scaled up and down to suit the application, once the basics are understood. The mast being  made is for a Mayflower sailing dingy and will be demonstrated by Marcus Lewis.


The process is demonstrated in the accompanying video clips with a step-by-step guide. The conversation with the boat builder, in this case, Marcus Lewis is unscripted and covers the technique from his experience.

Part 1

  • Step 1 ~ the design and plan for the spar, in this case a mast for a Mayflower
  • Step 2 ~ planing the first tapers
  • Step 3 ~ marking the front taper
  • Step 4 ~ planing the front taper

Part 2

  • Step 5 ~ using a spar gauge to mark out the mast to convert it from 4 sides to 8
  • Step 6 ~ removing the corners to convert the mast from 4 sides to 8

Part 3

  • Step 7 ~ going from this 8-sided shape to 16 by removing the corners again
  • Step 8 ~ converting the 16-sided shape to 32
  • Step 9 ~ final planing from 32 sides to nearly round
  • Step 10 ~ using a sander to get the final round shape for the mast

Part 4

  • Step 11 ~ after the initial shaping, key measurements need to be checked
  • Step 12 ~ cut the mast to length
  • Step 13 ~ mark out the mast step and plane the taper
  • Step 14 ~ mark the top of the mast and cut the shoulder for the mast band

Part 5

  • Step 15 ~ mark out the mast’s sheath
  • Step 16 ~ fitting the mast band

Detailed Instructions

Step 1 ~ the design and plan for the spar, in this case a mast for a Mayflower

  • When making a spar it is important to match what  was actually designed for that vessel, with the spar’s weight and strength taken into account. Deviation from plans may have an  impact on the rig and also the stability of the vessel.

  • In this case the mast was for a Mayflower 14’ clinker dinghy, but there were no plans for the rig, so its design was taken from an existing mast and will be made in accordant to these measurements.

  • The overall length is 13’ 4’’ (4.06 m). This enables the mast to be stored within the boat. It has a diameter of 2 ¾’’ (70 mm) at the  point where it goes through the forward thwart and tapering to 2’’ (51 mm) at the top.

  • The timber for this mast will be spruce. When selecting the timber it must be as clear of knots as possible. It was prepared by running it through the thicknesser to give a 2 ¾’’ (70 mm)  squared piece of timber and kept longer than the overall mast length.

  • Mark out the key measurements.

Step 2 ~ planing the first tapers

  • With a power plane, plane the length of the timber down to the line. A clamp will help keep the mast still while planning. Using a suitable square, check the material is being removed evenly across the face and the face being planed remains square to the other sides of the mast.

  • Check the straightness of the taper by eyeing it along its length; any hollows or bumps should be marked up with  a pencil for planing.

Step 3 ~ marking the front taper

  • With a mast there is a tendency for making the aft face straight, this has the advantage of allowing the mast track to be fixed  and simplifies the front edge of the sail. As the sides have been tapered in step 2, it only leaves the front of the mast to be  tapered.

  • Eye down the mast to select the best side for the back of the mast. Then transfer all the widths to the mast, marking from the back edge. These will be used to run as a straight edge through to get the required taper. Use the sail track as a straight edge, as the sail track has a suitable amount of flex which enables it to pick up the pencil marks. Clamp the sail track in place. Once happy with the  line, use a pencil to draw along it to give a line to plane to.

Step 4 ~ plane the front taper

  • Once again using a suitable power plane, plane away the excess material to form the taper. Check for high spots during the process and make sure the face is square with the side faces of the mast. On completion, the mast will have 3 tapered sides and a straight back face already for the next step.

Step 5 ~ using a spar gauge to mark out the mast to convert it from 4 sides to 8

  • The aim for this square piece of wood is to make it into a round mast. This is done by removing the 4 corners, resulting in 8 sides,  and then removing those 8 corners and so on. Each step brings it closer to a round shape.

  • The important outcome of this process is that all the sides’ lengths are equal, this is where Pythagoras’ theorem comes into play. Pythagoras’ theorem states that in any right angled triangle, the area of the square whose side is the hypotenuse (the side opposite the right angle) is equal to the sum of the areas of the squares whose sides are the two sides that meet at a right angle. So the Pythagorean equation can be written:

    a2 + b2 = c2
  • To create an octagon section from a square, it is necessary to plane or cut the 4 right angle triangles off. Due to this relationship,  we can use Pythagoras outlined above to calculate the ratio between the sides of the triangle, square and the octagon.
  • From the above diagram, it is possible to see that side a and b are equal and side c is not only the hypotenuse of the triangle but also the sides of the octagon. This highlights the relationship between the sides and enables a spar gauge to be designed.
    To find c, the equation can be rearranged to:
    c = √( a2 + b2)
  • If you give a value of 1 to sides a and b (a and b are the same length as the corner angles are 45°, 90° and 45°), c can be calculated as being :
    c = √( 12 + 12)
    c = √( 1 + 1)
    c = √2
    c = 1.41
  • So the relationship between sides can be described by the ratio 1:1.41:1. If the spacing between the outer pins and inner scribes on a spar gauge uses this ratio, it will mark out the octagon within the 4-sided shape.

  • As long as the outer pins are pressed against the side of the mast, this ratio will be transferred to a tapered or straight mast as the spar gauge is drawn along the timber. Ideally the spar gauge needs to be at an angle of 45° to the mast, as a different angle will affect the ratio. For this reason you will require a different size spar gauge for different mast’s diameters, however, the spar gauge will do a range of spar sizes within reason.

  • Once these corners have been removed to create an octagonal mast, it is necessary to remove these corners. It would be possible to make a spar gauge for this purpose, the ratio in this case would be 0.4005 : 0.199 : 0.4005 between the various components of the spar gauge.

  • Once you have made your spar gauge with its wooden or metal outer guide pins and the inner scribes (these could be pencils, metal spikes or even screws), you will be ready to mark up your spar.

  • The benefit of the gauge is that while the outer pins are pressed against the side of the mast, that ratio (1:1.41:1) will always happen and this is true for both tapered and straight masts. This removes any unnecessary calculations, marking outs, etc.

  • So place the spar gauge on the piece of wood, twist it so the guide pins have made contact with sides and draw it along making sure that the scribes (in this case screws) are marking the timber. To make the line easier to see, a pencil could be run down them. The lines give the edges of the corners which must be removed to make the octagonal shape required.

  • Measuring the distance from the edge to the line at different points along the mast demonstrates ratio at work. As the width changes due to the taper, the distance from the edge to the line also changes and a range of 14mm to 21mm was seen.

  • Rotate the mast and repeat the process for each side.

Step 6 ~ removing the corners to convert the mast from 4 sides to 8

  • Using shaped blocks will enable the mast to be held so a corner of it is uppermost; a simple case of rotating the mast by 45°. Then use a hand power plane to remove the corners down to their lines. For each planing pass, it is best to work the entire length of the mast. Obviously further up the mast the less there is to remove, so alter the depth knob on the planer to adjust the amount which is being removed. This allows a smooth change throughout the mast. The lower section may require more work as there is more to take off.

  • It is important to keep an eye on the lines as you work your way up and on each pass. Once you have come down on to the marks, set the planer to a fine cut and remove the final amount of wood.

  • This process is repeated for each corner, and a after a lot of  walking and a pile of planer shavings, the 8-sided mast has been created.

Step 7 ~ going from this 8-sided shape to 16 by removing the corners again.

  • So in this step the mast will go from 8 sides to 16 by just planing the corners off again. As mentioned earlier, it is possible to  make another spar gauge which can mark out the corners. However, in practice it is usually done free hand, drawing on the shipwright’s experience and careful planing.

  • The increased number of sides, can make it possible to lose which corners have been done and which are still to do. So to make that easier, mark the mast with a continuous line, and to aid labelling of this line make sure it is in a spiral. Then number the faces using odd numbers, this allows the extra faces generated by planning the corners off to be numbered.

  • Some hand power planes have ‘V’ grooves on their bases, these help keep the plane on the corner. Again the depth of the cut will vary along the mast; towards the top the diameter is getting smaller and so will the sides of the 16-sided shape. A lighter hand power plane will be useful for this process, as the depth of cut can be from nothing to 2.5mm. For this small spar, 2 to 2.5 mm will be suitable for the base reducing to a 1 to 0.5 mm at the top. The use of the depth knob and adjustment along the spar may enable the corner to be removed in a single pass.

  • It is important to do a test plane to get the cut right, this should be down at the base which will give your maximum cut, reducing down further up the mast. Rotate the mast so the next corner is available to be planed, reset the planer to the correct depth and start again. Once all the corners have been removed, it is important to number all the newly planed faces which will be even numbers; hopefully, there will be 16 in total.

Step 8 ~ convert this 16 sided shape to 32 by removing the corners

  • The spiral line is important in tracking the removal of the corners, because soon the sides / faces could be as small as ¼’’ (6 mm) wide. So getting out of sync or setting the planer incorrectly may easily cause a corner to be removed when it shouldn’t be.

  • Choose a smoothing plane to remove the corners, thereby increasing the number of sides from 16 to 32. This takes a little more effort but increased control is required compared to a power hand plane. With each stage of removing the corners the mast is getting rounder.

Step 9 ~ final planing from 32 sides to nearly round

  • There are several ways of achieving this step, which again requires the removal of the corners! It may be possible to use a round bottom plane (wooden spar plane). The radius of the plane base indicates the size of the spar they would be used on, and some of these can be very old. These wooden spar planes can rip the grain so care is required to use them. It is a question of taking the corners off and removing the high bits without tearing up the grain too much.

Step 10 ~ using a sander to get the final round shape for the mast

  • It would be possible to mount this mast in a lathe and use sand paper to smooth the mast as it spins. An alternative to spinning the mast is to keep it still and spin the sand paper instead. For this latter option, use an electric drill with a block of wood mounted on a long bolt, a boss to hold it in place and a standard sand belt turned inside out. Loop the sanding belt onto the mast, spin up the drill allowing the block to turn. By pulling back on the drill, the friction powers the belt, and you can work up and down the mast and rotating it to enable the spar to be sanded. This process of sanding will hopefully remove the final corners and make it fairly round. To check the roundness and feel of the mast, run your hand up and down it.

Step 11 ~ after the initial shaping, key measurements need to be checked

  • Using the drawing, make sure that key dimensions are correct to the drawing. For diameters use outside callipers to check for size and roundness. Mark the mast foot by drawing a line round a mast. To do this it is always useful to use a piece of material like a sanding belt. Wrap it around the mast so the edges line up together and on the mark, take a pencil and draw a long the edge so a line is drawn which is square to the centre of the mast.

  • Now mark the mast top; its length is 13’ 4’’ (4.15 m).

Step 12 ~ cut mast to length

  • Use a crosscut handsaw to cut the base of the mast off.

Step 13 – mark out the mast step and plane the taper

  • The lower end of a spar does not have to be round, often they are octagonal and they can be square. In this case it is going from a round section to tapered square section with radiused corners

  • Find the centre of the mast using a suitable ruler and then mark the mast step which is 1 1/8’ (29 mm) square. The taper running down to this square starts a maximum 14’’ (356 mm) from the base where it runs out to nothing.

  • Using a power hand plane, plane the taper on four sides of the mast, removing the wood down to the drawn square at the end. It is important that they are square to each other. Usually working the opposite side first gives good results. Once all 4 have been done, radius the joining corners with a smoothing plane. After this a light sanding is the only thing needed to complete this section of the mast.

  • It is necessary to then sand the whole mast to remove the circular scratches which are left by the sanding belt in step 10

Step 14 ~ mark the top of the mast and cut the shoulder for the mast band

  • With a tape measure, measure from the foot of the mast 13’ 4’’ (4.06 m) to the top of the mast and mark. For this mast, its length is the longest length which will fit within the dinghy itself for storage, this requirement has driven the design for the spar.

  • At the full length and using the callipers again measure the diameter of the mast; it should be 2’’ (51 mm). The internal diameter of the mast band is 1 ¾’’ (44 mm) which is the diameter of the required shoulder. Offer up the mast band, leaving a little amount of wood showing at the top, and mark the start of the shoulder. Draw both lines round the mast using the same technique as before with the sanding belt. Place the belt around the mast lining up with one of the marks, making sure the edges meet indicating that it is square and draw along the edge.

  • Taking a handsaw, cut along the shoulder line no deeper than the required diameter so the router will have a nice clean line to work to. Then mark the top of the mast with a saw cut. Calculate the difference between the mast diameter and the internal diameter of the mast band, halve it and this is the cutting depth for the router. The mast band was 1 ¾’’ (44 mm) and the mast was 2 1/16’’ (52 mm) giving a difference of 5/16’’ (8 mm). So setting the route to half that depth, 5/32’’ (4 mm) will give the correct diameter for the shoulder.

  • When working with imperial measurements, to quickly work out half of a fraction such as 5/16’’, simply times it by a ½. This will mean multiplying the denominator (the number on the bottom) by 2 (16 x 2 = 32) and the numerator (the number on the top) by 1 and thing multiplied by 1 stays the same (5 x 1 = 5). So a half of 5/16’’ is 5/32’’.

  • So setting the router to 5/32’’ (4 mm), it is useful to then check the cutting depth on scrap piece of wood before using it on the mast just in case the depth is wrong. Placing the router on the mast, keeping the base plate level, rotate the mast a bit at a time, routering away the excess wood to form the shoulder.

Step 15 ~ mark out the mast’s sheath

  • The sheath must be set in the mast as high as possible however not too close to the mast band so it doesn’t get tangled with any of the shroud wires. It is very easy to mark the slot for the sheath slightly askew so by drawing the lines of the slot on masking tape and then sticking this to the mast, it is easy to eye up the position of slot and adjust if necessary.

  • As the diameter of the mast is 2’’ (51mm), this will determine the diameter of the sheath which will mean that a 2 ¾’’ (70mm) slot will be required. Give room at the bottom of the slot for the sheath to clear and the sheath plus halyard at the top. It is a 8mm halyard so 10 mm sheath is required. Start with marking the centre of the tape, then 5 mm each side plus the required height (2 ¾’’ (70mm)). As this has been drawn on the tape, it allows easy adjustment to make sure it is on the required centreline of the mast.

  • In the accompanying film clip, cutting of the slot is not demonstrated, however, it can be cut either using a mortiser machine if available or a chisel.

  • Time to cut the mast to length and see how the mast band fits.

Step 16 ~ fitting the mast band

  • Offer up the mast band, and if the shoulder is a little over size, use sandpaper or a wooden file to adjust the fit; it should be tight. By knocking the mast band on, it will show where it is tight. Continue this process until it fits well.

  • All that is left to finish the mast it a bit more sanding, cut the slot and then it will be ready to be sealed and varnished.

  • The mast being made was used for the first Mayflower dinghy to be built by Marcus Lewis (build number 101) and hopefully the first of many.
Kies Taal...

Benodigd Gereedschap

  • Mast design (drawing or pattern of mast to copy)
  • Saw horses
  • Spar gauge
  • Clamps
  • Straight edge (aluminium sail track)
  • Mast blocks
  • Hand plane
  • Hand saw
  • Electric planers
  • Mast round planer
  • Electric drill
  • Sander
  • Router
  • Square
  • Personal Protective Equipment (PPE)
  • Pencil

Benodigde Materialen

  • Suitable wood i.e. spruce