...hmmm, what? Oh,yes. The Mast!

Wherein I build a hollow core "birdsmouth" spar.

Updated 11/02/25

Once again I find myself at loose ends. All good jobs come to those; ends, loose and otherwise. This past one was pretty OK. Somewhat recently I got the bug to start a part of the boat that's been rattling around in my brain pan for eons, namely said mast. As I'll describe later on, I started gathering the makings for the table 6 years ago. Nowadays that's pretty eonish.

The cavern below me has been all but abandoned to the trogs and spiders ever since I stopped playing with trains. It's staggering how much downright junk one can accumulate even when not actively trying.


Accomplishing this bit took my brother the better part of a week. Sadly, he didn't throw out the junk. He merely rearranged it in another corner of the basement.


Activity didn't pick up again until late June when the table began taking shape. The steel stud legs and framing are from a jobsite scrap pile where I worked in 2001. Industrial grade studs.


The top is 3/4" plywood. The table is 42'-3" long. There are a few dips in it, but the front was set with a string line, and it's absolutely straight.


First coat of primer, meaning it got a second coat, and the beginnings of a band saw. No. I'm not normally a "two coats of primer" kind of guy, but I was hoping the primer would whiten the table enough to get away with not painting. As you'll see, it got painted. Once.

The band saw was inherited and was supposed to replace the antique in SWPUWM's studio, but the damned thing refused to grow little feet and walk itself inside. So until now it's been gathering a fine layer of dust in the garage.

I should have left it there. What a royal pain in the ass it's turned into. I seemed to have gotten a motor with it. The motor is 220 volts, so I had to run a seperate 220 line for it. It wasn't wired so I had to wire it up. I sent Mongo a shot of the label and he decyphered the wiring diagram and told what to connect to where. (I'm an electrical moron.) Then I broke the first switch as I was installing it, so off to the store to buy another one. Then I wired the circuit braker to a cold leg on the panel. Mongo came over and fixed that little snafu.

All the electrical nightmares out of the way, we turn on the saw for the first time. And the rubber bands surrounding the wheels promptly jump out of the slots! We surmise that the wheels are turning too fast. I have another pulley wheel down at the shop, so it's another trip across town... and another day the saw isn't running.

Change wheels. Slow down the motor to about 1100 rpm. Turn it on. And the bands jump off again. This time I suspect the problem is fatigue. (Although "brand new", the saw is 20 years old. After a discussion with Mongo, I decide to glue the rubber bands on with contact cement. I search the house. No contact cement. It's about the same distance to the store as the shop, so I go back to South Philly to get the cement.

Wheels properly glued in place, the saw runs like a saw, only the blade's no damn good! Doesn't cut worth a shit! McMaster-Carr is shipping two top of the line blades on Monday.

I can only wonder what kind of fiendish plot it's cooking up next. I just hope the saw doesn't bite off a finger in retrubitution for my years of wanton neglect.


Back to the story. I welded up a very sturdy little stand for the saw. M.L.Condon delivered 200 linear feet of 3"x6" Rough Sawn Vertical Grain Douglas Fir in lengths 12' or longer. It used to be called Quarter Sawn lumber. Now it's called Vertical Grain. It's beautiful stuff. I have 14 pieces and there might be 3 knots in the whole lot; small knots.

I chose this option, meaning rough sawn, because the price for "dressed four sides" was downright staggering.

Beginning to approach some semblence of order - sixteen bags of trash stuffed under every nook and cranny of the table awaiting trash day.


Here's the little monster. If it doesn't work with the new blades, I have a good mind to put a couple of bullets between its eyes.


The lumber is coming off the table and stacked in the foreground. The table gets its coat of paint.


Today, 07/07/07, got off rousing start. I began by laying out in full 1-to-1 scale one of the staves. The staves are all typical. The reason for the full scale lofting is that the lumber lengths are to some extent random. In order to get accurate measurements for the various bits; each stave will have to be scarfed from at least 3 pieces, I want to be able to measure the width of a stave at any point along its length. (Extremely tight string lines are a very accurate way to mark material; ball-point points are dropped under the line, then a straight edge makes the permanent lines.


In case you're not too sure what a "birdsmouth" is, it's a system for building hollow spars. It's also refered to in Practical Junk Rig as the Noble System. This is a cross section shown at the "datum", the point where the mast passes through the deck. Most of the mast is made up of only the outer ring of rectangular pieces. Each piece has a notch cut out of one side. hence "birdsmouth." The trapazoidal pieces are stiffeners that thicken the mast up a short way above and below the "datum."

This mast will be 37' long. It is (will be) 10.5" at its maximum diameter at the datum. It will taper to 8" at the foot, and 4" at the head. (Not to get too technical, but it is cylindrical just above and below the datum too.)


Fresh paint and ball point pens make for very clear, permanent lines.


Here's a view of the datum section of a stave. The part between the vertical lines will be cylindrical, short taper on the left, long taper on the right.


The 3 pieces of stave "A" have been cut for width. The overlap is where they will be scarfed. The scarfs will be 10-to-1, somewhere between 8-to-1 "just barely enough", and 12-to-1 "fanatical."


Except for these two, which are 8-to-1 because I wasn't paying attention. I'm not too concerned though for several reasons. First of all, they're going to be surrounded by solid staves on either side. Those two "stumps" will in all likelyhood be the only short pieces on the foot side of the datum. Secondly, the sheer massiveness of this portion of the mast means there won't be much if any flex to worry about.


It occurs to me now that you're probably wondering just how I'm cutting the wood. If not with the band saw, then what? Let me introduce you to Bosch Monster. It's an 8-1/4" saw that cuts very nearly 3" deep. The motor is 13 amps. A bull. A beast. Verily, a monster.

When it doesn't actually reach to the bottom of one of these 3' cuts, there's so little wood left I can cut the piece apart with a couple of strokes with one of my Japanese pull saws. There's very little dust to speak of. I merely had to adapt and install one of my multitudinous vacuum cleaner nozzles to the sawdust port and it was off to the races.


Timely update 07/07/09

Staves "A", "B", and "C" areare cut and scarfed for width. Cutting for thickness remains to be done. Hopefully the band saw will some into play. But failing that, I'm fairly certain now that a combination of circular saw and jig saw will get the job done.


Time to refer to our sophisticated material utility document to determine how to cut "D".

"D" is in progress.

Progress Report: Quatorze Julliet - Bastille Day!

It's off to the beach! Notorious boatbuilder feigns excitment for SWPUWM; secretly fumes about pissing away two days away from the mast.


The first four of the eight staves are all cut for length, width and thickness. Stave "D" is gluing up first because it was the closest to the edge of the table. Careful perusal will show that there is indeed a very short piece among the "A"s (on the right.) It was very late on Sunday night and when pulling the uppermost piece out to cut the scarf, I turned it over a quarter turn, cutting the scarf into the wrong face. The replacement is a 4' patch.
The reasons I'm finishing these four except for the birdsmouths is that I'm beginning to accumulate a lot of scrap and in order to build the rest, some are going to be made from reglued scraps. See below. Also, I'm beginning to run out of table room and this way I can stack the "made" pieces against the wall.


OH! I take back all the nasty thoughts I had about the band saw. Well, maybe not all of them because it had one parting shot in impinging my progress. I got the new saw blades promptly from McMaster-Carr so I started taking off the old blade... only to discover that in my attempt to put the on-off switch in a convenient place, up front, I'd locked the blade in between the saw table and the motor. Notice the $43 worth of NEW plugs between the motor and the on-off switch.

I must say though, it cuts like a dream come true. The blade is bimetal, 1/2" deep, and about 3/64ths thick, with 6 teeth to the inch, and has a noticeable "set". Anything under four inches thick, which it cuts with ease, and it chomps through as fast as I can push the wood through. Cuts straight too.

UPDATE: 07/07/30

The glued pair of scraps above worked out very nicely. It went on to become one of the base pieces. The next one however was an utter disaster.
Mea culpa. Only twice in my recollection have I mixed my epoxy backwards; that is to say, 2 parts hardener, 1 resin. This was one of those two. (The first time I was able to recover.) This time not so.

Late one night I thought I'd get just a bit more work done, be a bit more advanced for the next day. I chose the pieces to glue together and placed them on sawhorses. Then I mixed the "soaking coat" painted it on and went off to give it time to work in. Not realizing I'd botched the mix, and it still being glossy and tacky, I mixed the thickened coat, the real glue, applied it and clamped up.

The next day there were sticky edges to the glue-up. That definitely shouldn't have been, so I knew immediately I'd messed up. What to do? The reason I mentioned the previous time this happened is that that was a section of glass on the inside of the hull. To that mess I applied, ( if I remember correctly,) straight resin. It went on to cure solid in a timely fashion. I hoped that by giving this mess more time, it might also cure. Such however was not to be. After more than a week, I was able to drive a chisel into the crack at the joint. Definitely bad news. So I condemned the piece. Although not good as a stave member, it went on to usefulness as parts of the step octagon.


Brother Andrew brought his spiffy new table saw. Here we see the members of the datum reenforcement being cut. Note that he left the blade guard home. I cringed but noticed that his 9&3/4 fingers - he gave up a thumb tip to a radian arm saw several decades ago - made him all the more careful around the blade. No blood stains on my lumber. All's well that ends well, I guess.


All eight pieces are gluing up prior to being mitred for the octagon. Scrap ends were piling up, but there wasn't a lot long lumber, and rather than lose more length or cut up wood that might prove useful later on, I elected to join these pieces with a simple half-lap.


My reasoning is that this is mostly a compression stiffener since the mast gets wedged in at the partners.



During the week between the picture above and the one below a lot happened. All the staves were finished and I turned my attention to cutting the birdsmouths. A long time ago when I first began dreaming out this phase, I'd always thought of using angle iron as the rails for the rolling upsidedown table saw. I called an old employer and order 80' of angle several weeks ago. When I got the call telling me it was in and found out how much they wanted for it, I almost fainted. (The amount of this stuff that gets wasted is appalling.) So I cleaned the shop and waited for delivery. And got stood up. One whole day wasted. They never even called. I haven't called them either. I'll probably never work for them again either. It brakes my heart.

In the mean time, I realized I could achieve the same ends with lumber; 16' doug fir 2x4s and some "one by". (The one-bys are underneath.)


I drew a scale drawing as a stave profile to give me the desired elevations for the bunks between the rails. Along with the other tapers, the birdsmouths are tapered. This means the top of the stave has to slope down towards the tip. The stave has to be braced up along its length so that the bottom of the cut is at the same height at the tip as it is at the fullest part - the datum. You definitely need a drawing to figure that out when dealing with a spindly wobbly piece of wood 30+ feet long. Installing the rails and bunks was straight forward stuff. Boschmonster needed a fair bit of combobulating to become a rolling upsidedown table saw. I widened the base, added an aluminum brace at the back end, and screwed a fence to one side. This screwed fence had to be removed as the blade isn't quite parallel to the table. Hence the C-clamped fence.


Looking straight down at the birdsmouth groove in the center - This was my very unimaginative system for centering the staves between the rails. Again, late at night. Brain winding down to dead stop, but it worked for the first one.


Brother Andrew came along the next day and suggested this truly elegant solution - lag bolts, heads into the center, easilly loosened or tightened to center the stave between the rails. Mahvellous! The only irritant, so to speak, was that the vacuum cleaner could only be attached to boschmonster on the outboard cut because of the way I'd attached the nozzle in the first place. I must be getting finicky in my old age because when it looks like I'm going to have to chop my way through the airborn sawdust, I wear a mask. Oh, and I've probably gone through fifty pairs of latex gloves for this project alone.


Staves are gluing up as pairs. The first pair (of staves) was assembled with ratchet straps, but as it turned out, they didn't apply the pressure exactly where it was needed. So I finished by clamping up with bits of kant strip. The second pair, on the right, have full length kant strips screwed in along the length, and clamps at each screw. The glue up is near perfect.

Feb -2011 - Found some lost material...


Unable to gather a team to assemble the entire mast in one swell foop, I glued two staves together at a time, then four staves into half-masts.


Here we are at the base of the mast. The heel and datum stiffeners were glued into octagons. The lightning conductor , ( green, not visible, is on the bottom of the far piece,) and the nav light power conductor, (white), were run the length of the mast and fished through the datum stiffener in preparation for finall assembly.


Here at the masthead, the conductors are plainly visible, both fished through the masthead stiffener (bathed in goop.)


Here's another view of the mast cavity near the head. The piece on the "bottom", at right, was liberally stuffed with aluminum foil just before final assembly. I'm hoping this acts as a radar reflector. If not, I'll add one of those masthead gizmos later on.


This is it! The big moment! It's a mast! Since it was only possible to clamp the two halves normally at the very slim mast head, I screwed the birdsmouth scraps to the sloping sides of each halfbefore assembly. This gave me parallel sides to clamp with.


Here at the base, the clamping setup is plainer to see. Once again, the boatbuilders' adage, "You can never have too many clamps.", was proven.


Now this is a mast!


Fairing began with a Makita power planer to bull off the grossest angles. Then I switched to a 16" vintage Stanley Jack plane here and there. Once it was beginning to look circular, I again switched tools; a Makita 4x24 belt sander with, 24grit, then 40grit, then 60grit. The belt sander was too cumbersome and heavy. The final sanding was done with a Bosch Random Orbital sander. Up and over, up and over, up and over, always on the bias.

The whole mast was sheathed in 1708 tri-axial glass. Oops, no picture.

Depending on how you got this far, you may have missed some pages I forgot to write about.
2005 - Building the ladder.
2007 - Skylight - The Real Part I of 2007

This way to 2011 - Part I

This way --> [home2.] Home.[chaos]

Got any questions or comments? I'm still "themadmac" [dawg1email.jpg] only now I'm at verizon.net

Written 2007/Jul/07
Updated 2011/Feb/25