Make a Solid Boat Mast
Most folks will never need to make a mast for a boat, but they may wonder how it's done. You may find yourself wanting to make something mast shaped, only smaller one day, however. Maybe you'd like to make small flagpole, or even something as small as a walking cane. This article shows you how to make any square (in cross-section) length of wood into a perfectly round one without using a lathe. Most boat masts are tapered, and this method works with either a straight or tapered mast.
Steps
- Determine the length of your mast as well as its diameter along the length. For instance, you may have a mast that is 3" in diameter at the base tapering up to 3 1/4" 1' up the mast, and then tapering down to 2" starting 1' from the top. Here's a picture with an absurdly shortened mast for clarity.
- Select a light, straight-grained wood for your mast. Sitka spruce is wonderful, but boat builders have been using whatever was available for ages.
- Cut your wood to be a little wider, thicker, and longer than your mast. Glue up two boards to get the desired thickness if needed.
- Use a jointer or a hand plane to plane one face of your mast perfectly flat.
- Mark the center line of your mast on this planed face. Stretch a string tacked at the midpoint (widthwise) of both ends of the mast and pull it taut. Make small pencil marks directly beneath the string to mark your center line.
- Use a long, straight strip of wood (called a batten) the length of your mast or longer, to connect these marks and create a center line along the face of the mast. Repeat this process on the opposite face to create a center line there as well. It doesn't matter if the two faces are perfectly parallel to each other just yet.
- Mark the width of your mast along its length, using your center line to make sure that your widths are centered. In this case, you'd measure out 3" at the base, (i.e., 1 1/2" to either side of the centerline), move up 1', measure out 3 1/4" wide, move up one more foot, measure out 3 1/4" again (since this is where the transition to the top of the mast begins), and then go to the top of the mast and measure out 2" wide. Repeat this process on the opposite face.
- Use your batten to connect the width marks along the edges of your mast on the planed face. Repeat this on the opposite face. You now have an outline of the shape of your mast on two opposite faces.
- Cut the outline of your mast with the planed face down using a band saw, circular saw, etc. Cut close to, but not right on, your outline. You now have two sawn faces, one planed face, and one untouched face.
- Plane each of your sawn faces flat and smooth, making sure that they are perpendicular to the first flattened face. Check your progress with a combination square as you go. You now have two tapered sides that are flat (side to side) and perpendicular to one face. This means that they will also be parallel to each other.
- Repeat the steps for marking the center line and mast outlines on the two faces you just planed. Then cut the outline again for these two sides.
- Plane the sides that you just cut flat and perpendicular to their adjacent sides. You now have a tapered spar that is square in cross section and is exactly the right width along its length.
- Use a compass to draw a series of circles along your mast that just touch the edges of the mast. Do this on all four sides. At the very least, draw circles at the top, bottom, and transitions of your tapers. Draw at least one circle in the midpoint of your tapers, and at least one circle in the midpoint of your mast. These circles will generate the points that you will eventually plane down to, so take your time and be precise.
- Draw two lines that just touch the edges of your circle, and that are perpendicular to the edge of your mast. Do this for each circle. What you've created here is a cross section view of your mast; you've got a box (the current mast shape) with a circle in it (your final mast shape).
- You can get by with only doing one vertical line next to your circle, but the more reference points you make, the more checks for accuracy you'll have.
- Put the point of your compass in the center of the circle, and open up the compass until the pencil point just touches the corner of the box (i.e., the point where the line goes off the edge of the mast). Lock in that measurement.
- Read the next 3 steps before making any marks, you may want to take the shortcut described in step 18 to save time.
- Make the edge marks for the 8-sided mast. Take the compass with the setting you just locked in, and placing the point as close to the corner of the box as you can, tick off the distance on the line that makes up that side of the box. Make a little horizontal mark where the compass intersects the box line.
- You can clamp a piece of wood to the mast so that your point is exactly half on and half off the mast.
- Go to the opposite side of the box and do this again, now going up the line. Repeat this on each box line.
- Check to make sure that your tic marks are accurate by taking your combination square and checking that a 45 degree angle taken from the side of the mast and going through this marked point on the box line will just touch the circle. In other words, the tic mark you just made identifies the point on the side of your box where a 45 degree line that is tangent to your circle will just touch.
- Shortcut:If you want to skip the part about using your compass, you can create these tic marks on the box side using just your 45 degree combination square, making sure that you draw your line so that it just touches the circle. Using both methods from time to time as a check is also a good idea.
- Mark the edges of the 16-sided mast.
- Set a protractor (or in this case, and much easier, a protractor head on a ruler) to 67 ½ degrees. Each corner of a 16-sided mast is 22 ½ degrees, and 67 ½ is 90 degrees minus 22 ½.
- Place the blade tangent to (i.e., just touching) your circle, and mark on the box side where the blade crosses it.
- Draw a short horizontal line there as well.
- Repeat this around the circumference of the mast using at least one side of your box.
- Continue your lines past the box side to where they intersect. If they intersect exactly on the centerline of the mast, you know you're on target. The picture to the right shows a quick summary of the lines drawn. The whole point of making these is to get the proper intersections for the edges of your mast as you start planing it down.
- Connect the tic marks you've made for the 8-sided mast along the length of your mast with a batten, and draw the resulting lines. In this photo the batten has been clamped to the mast. This way you don't leave little nail holes in your mast from fastening the batten.
- Do the same again with the 16-sided lines. You now have the edges of an 8-sided and a 16-sided mast drawn.
- Clamp your mast down using angled clamping blocks to hold it steady.
- Start planing the first corner.
- Plane down until you just connect the 8-sided edge marks on each of the adjoining faces.
- When you're done planing down all four corners you'll have four new faces that look like this. You can see that the non-planed faces have guide marks on them for the 16-sided mast, but of course the newly planed faces don't. You’ll need to add in guide marks for the 16-sided mast on these newly planed faces.
- Take your compass and measure the width of the 16-sided face.
- Transfer that width over to the planed side by putting the point of the compass on the existing 16-sided line and making a tic mark on the newly planed face.
- In this photo, the tic mark and line had been previously drawn, so the compass is just in position to show how the line was measured.
- Place a batten connecting your marks and draw a line along it. At this point, you may need to do some minor adjustments if it looks like you won't get even widths between each of the 16 sides. Use your best judgment and be brave. In this photo you can see where the upper line was adjusted to make it fit better with the other sides.
- Plane the corners down to these lines to get to a 16-sided mast.
- Now you don't have any guidelines to help you get from a 16-sided mast to a 32-sided one. Instead of making new longitudinal lines, take a number of locations along the mast and connect the tips of the edges you've created with lines like this. It looks like a Charlie brown shirt.
- Plane off the tips of this zig-zag line, leaving just small line segments behind. This will give you a visual guide as to how much you're planing off. It's not much, just a few strokes of the plane.
- Suspend the mast so that you can both hold it steady and rotate it as you work. It’s useful to put screws in the end and fasten it to a pair of uprights clamped to workbenches.
- Here's a fancy box sander used to finish off the rounding. You can make a simpler one by making a 3-sided box and stapling sandpaper in the open fourth side. There are handles on this one, as well as a cloth backing behind the sandpaper to help keep it from tearing. Clamps along the sides of the box hold the sandpaper in, and these make it easy to change paper.
- Sand away! When using the sanding box, move in a long, spiraling motion along the mast. You can go straight back and forth for a few strokes, but mostly use a long twisting motion around the mast as you go. This helps to fair out any uneven spots. Start with 60 or 80 grit paper and work your way up the grits to 150 or so.
- Varnish, starting with a slightly thinned varnish mixture to soak in. Follow this with a minimum of six coats of marine varnish. Eight to twelve coats are better, and will save you work in the future.
Tips
- Keep your tools razor sharp.
- Use a longer plane for most of this work, like a Stanley #5 or #7, to get a nice fair line. A scrub plane, or drawknife are both excellent for taking off the bulk of the wood when going from 4 to 8 sides.
Things You'll Need
- Exact measurements of your spar, including length, diameter, starts and stops of all tapers, and material to be used
- A strip of straight-grained wood for a batten - it should be about 3/4" x 3/4" square and cut as straight as possible. Spruce is an excellent choice.
- A compass
- A combination square
- A protractor head for your ruler or a protractor with an extending leg
- A drawknife
- Wood planes: scrub plane is nice but not necessary. A #4 or #5 is good. A #7 is great for long straight runs.
- Sharpening stones to get your blades razor sharp
- Space to hold your spar while you work on it
- A sanding box
- Sandpaper
- Pencil, string, and nails to hold the string tight
- Glue, in case you're gluing up your spar from 2 boards.
Related Articles
Sources and Citations
- http://eweandme.com/boatblog A blog about attending wooden boat restoration school.
