Mast construction

[dadellwo]

I am finishing a Swampscott Dory and am making a mast out of Norwegian Spruce. It is rough cut to a 13 foot long tapered square pole. I am to make it a round mast, 3 inches at bottom, 2 3/4 inches in middle and 1 3/4 inches at top. Is there a place I can look to see how I can do this nicely and not ruin a great piece of wood? I have mostly hand tools.

[gert]

I ruffed mine with a power planer and finished up with a well tuned and sharpened 24" armstrong jointer plane. It didn't take that long and when a plane that long (heavy) gets started it will go the entire length of the mast taking a single shave. Cut some circles in card board and cut em in half to check your round.

[mmd]

Bud McIntosh & Sam Manning's book "How to Build a Wooden Boat", Chapter 18, "Spars". A very clear text and excellent illustrations. This text should be on every boatbuilder's shelf.

[Paul Scheuer]

All of my experience with making round stuff out of square stuff has involved making a perfect octagon to exact marks on the four faces. I once saw an article on a marking jig that did the outlines and the center marks on tapered pieces. It may have been in WB. The real trick is the shoe-shine with a coarse sanding belt action, until the center marks just start to fade. It's not that hard to get really good results. I've even been accused of turning my oars on a lathe. The same system works with oval shapes, as long as you do the marks right.

[DougWilde]

I built a 19'9" mast for my Windward 15.

This will take you to the page that shows how I built it, taper and all.

Mast, step, and partner page

The boat gets flipped tomorrow so I can paint the deck. Can almost hear the waves slapping her flat bottom.

Doug Wilde

[JodyAdamonis]

the first thing you want to do is find the widest cross section of your mast and cut a square block to that exact dimension. With a compass, draw a circle in the block so that it meets four of the edges. Next take a combination square and place the 45 degree side on any side of the block and adjust it so that is meets the outside of the circle. draw a line on a 45 so that it just touches the circle and proceeds to the edge of the block. do the same on the opposite edge. Take a second peice of scrap wood (this will become your marking guage) that is 1" wide and 2" wider than your block. Place it on your block and transfer the 45 degree intersections to the second block along with the outside dimensions of your circle. You should have 4 marks on your second block. The outside circle marks is where you will drill and insert 10d nails, these will act as fences for your marking gauge. make sure you drill your holes on the outside of the marks so that the gauge fits over the spar. The second pair of marks, is where you insert pencils that will mark your spar so that you have 8 equal sides. These holes are centered on the lines.
Next plane the corners to the line. A number 4 stanley should work fine. you should 8 equal sides. Now plane all 8 corners so that you have 16 equal sides. This can be done easily by eye. Once your have 16 equal sides proceed to round those corners off with a block plane until your remove all remaining edges.

Now its time to turn to 60 grit sand paper and sand until you are satisfied.

[Ian McColgin]

I put it up somewhere else but here goes the easy way:

Put the tapers for the sides and leading edge on your square stock. The luff is straight - a proper mast does not taper all around like a flag pole.

To make a scribing jig that will give you a great 8 side right through the tapers, figure a distance conveniently a bit larger than the largest square section that is easily divisible by 24.

For example: Assume a shape that expands from 1-1/2" at the heel to 2" at the partners and the tapers, but not evenly, to say 1" at the truck.

A distance of 2-1/4" is readily divisible into 24 units that are 3/32" each, so make a piece comfortably longer than that and drill it such that two nice round posts can stick down an inch or so with 2-1/4" clear between the inside edges.

Mark on center a spot 21/32" from each end (of the inside edges of your round posts) and stick through there whatever you want as a scribe. I like a fine nail but whatever.

You lay the stick across the spar stock at it's natural angle. This angle will decrease as you move from the heel up to the partners and then increase again as you move to the truck.

You'll be laying nice lines that put the lines 7 units from each end with 10 units between each. If you envision looking at the square end with your octagon drawn on the bottom there, and think about just the top edge for a moment, it will occur to you that the two diagonal sides to be planed away are the same as the part of the original face remaining. Each corner being planed off is a 45-45-90 triangle. The hypotenuse is the same length as what is supposed to be left of the original face. Hence the 7-10-7. Take one corner - lopping off two sides of 7 units each leaves a hypotenuse of so close to 10 units that you can't measure the error. Seven Squared plus seven squared (49+49) is pretty close to ten squared.

QED.

[Bruce Hooke]

Others have done what looks to me to be a good job of detailing the majority of the process. The one thing I would add is that you say "rough cut" -- before you can apply any of these methods you need to make sure your stock is reasonably square (i.e. that each face is reasonably close to 90 degrees to the adjacent faces) and that the you've got the planned taper applied to the square stock. If you don't do the former than everything else that follows will be off. If the latter was not taken care of when you "rough cut [it] to a 13 foot long tapered square pole" then this will take a little careful layout and some planning to adjust the taper to match the plan. The way I would do this it to select which face is to be the straight (luff side) of the mast and then on the two faces that are adjcaent to this face measure and mark the correct width at various heights, measuring from the luff face. Connect these marks and plane the face opposite the luff face down to these lines. Then, on this newly planed face, and on the luff face, again mark the correct widths at various heights, but this time working from the centerline of the mast. This will give you a little bit to plane off each side of the mast. Having done that you can proceed to making an octegon out of the mast and so on from there...

[Paul Scheuer]

dadel: Bruce is Dead On. If the first shaping is rough, all that follows will be rough. Anyone who has ever screwed this up will say that they thought they could make it up in the final shaping. The first square shape should be square, true, smooth, crisp, and otherwise perfect. Not just the scribe marks, but the piece itself actually cut perfectly. Made is if you intended to varnish it for show.

I’m glad no one has suggested using a router to cut the bevels. I think it’s the formula for disaster..

[dadellwo]

Thanks to all. I have been doing well with your suggestions. The mast is almost done and your ideas and suggestions made it work. Thanks again for all your help. DADellwo