Birdsmouth spars revisited

I've been playing around with the birdsmouth technique a bit, what I've discovered is a nifty trick for putting it all together. No doubt somebody else has tried this before. First of all, as long as any two opposite pieces are the same width, it'll come out right, this allows you to make ovals, or, if you feel like it, really weird shapes. What I used was flat-braid straps, I just stapled it on to piece #1 and then held piece #2 in its proper position and stapled it to the strap, then I held #2 and #3 together and stapled #3 to the strap, then I held piece #3 and piece #4 together and stapled the strap to #4 and so on to #8. Once all the pieces were stapled on to the straps I just un-rolled the whole thing and spread on the adhesive, rolled it back up, and clamped it with hose-clamps. Pretty damn cool technique, if you ask me.

Yokebutt.

 

Come on kids, poke a hole in my balloon will you! Let's get a conversation started, so we can all benefit in the end! Bloody *******!

Yokebutt.

 

Lately I've been amusing myself by cutting a shallow cove with the table saw on the inside of the sticks, and thus making the inside round too! Works for oval birdsmouth spars too, just takes a little bit more figgering....

Yokebutt.

 

I like the idea of using a strap; I have made a few small tests using tape in the same way.
Do you have a name other than the user ID; I get a little tick in my head when addressing “yokebutt”, I guess I can get use to it.

Gary

 

I have access to a lathe with 8' diameter and a 40' bed to "clean up" any rough edges. Or we could turn down a tree in 8 hours?

 

Sounds like a great method for assembly. I like the birdsmouth technique just wonder about swallow tail installation. Plugging the foot doesn't appear to be a problem, but rolling up all those staves with a birdsmouthed swallow tail???? There I said it!
Keep up the good work Yokebutt!!

Phil

 

Yes, I can certainly understand if duluthboats doesn't care to address my buttocks, just call me "yoke", my friends seem to think it applies well.

Now Phil, if you would just lay off the gay jokes, unless "birdsmouthed swallow tail" has a meaning in woodworking too! (but then again, I'm not a native speaker of english) actually, I don't know what a swallow tail "entails" in this particular instance, would you mind enlightening me?

Yokebutt.

 

Swallow tail is the name given to a plug installed in a hollow mast. The plug or swallow tail is installed at the point where the spreaders are to be installed. The ends of the insert are cut with v sections taken out. They are hollow and usually made of hardwood. The v sectioned fingers provide extra stength but cut down the weight of the insert.

Hope this helps

Phil

 

I've come up with several modifications to the bird's mouth technique to address the typical issues that come up during any built up spar construction.

I build the sticks as halves, first of all. I glue it up and assemble it as any other bird's mouth pole, but tape over the seams I don't want glue in. This allows me to open the spar and install hard points swallow tails and all. Putting a cove on the inside (yokebutt style) would make this job a lot more difficult and I don't like removing any more material then I need to. I usually design the mast and like to stick with the scantlings I've selected for the intended use, though I could factor in an additional 20% material to account for the cove cut on the inside, but I'm not sure of the need.

I've made oval masts with internal halyards and wiring, all the bells and whistles you'd expect to see on a well dressed spar.

As Phillip has pointed out, the swallow tail, refers to the ends of a tapered insert (hard point) You need hard points along the length of the mast. Areas like the gooseneck, gaff, spreader(s) stay and shroud lands, heel and head will all need some reinforcement from their attachments and the loading they exert. These areas may be to prevent collapsing the mast from compression of the gaff or gooseneck, support for spreader sockets, shroud tangs, anything that may require fasteners that could compromise the stave wall. Typically a hard point is inserted in this area, with gently tapering ends to spread the load. More importantly to not create a "hard spot" which will likely break the mast when under bending loads in use. When making a built up mast, these inserts will have to taper down the inside of each stave, which must have look like a swallow's tail to some really bored spar builder long since dead, but his hook still carries on. I make mine up individually and glue them into place inside each mast half. I find it's a lot easier to fit them and insure good gluing surfaces this way. Tapers are around 12:1 or better.

I also use an asymmetric layout for the staves, rather then the more usually seen symmetric notch. I take advantage of the thicker shoulder created and save a small amount of rounding effort. I do use the symmetric layout on internal halyard spars.

 

A post in the steel boat section is from a guy who needs help on a mast specified in his plans . He can't nail down a few steps. His name is Phillip and I took the liberty to tell him to post on this section. Could you steer him straight? Rich

 

Phillip,
I think the roll-up technique would lend itself to leaving two of the joints dry and installing local reinfocements before closing it out, but I'll have to do some experimenting to confirm that.

PAR,
Cutting a cove on the inside was something did mostly because it seemed like a really cute idea, but the reality is that as you move materials away from the neutral axis their impact on stiffness increases by the cube of the distance, so I imagined the cove as a way of eliminating a little bit of material that doesn't contribute all that much to overall strength of a spar that gets forced to bend while sailing would be a good idea, I certainly appreciate your concerns about the difficulty of installing local stiffeners though.

The idea for bands to hold the pieces together arose from a teak and maple floor-board project we were doing at the same time that I was futsing around with the birdsmouth technique. What we did was to first glue together 2" thick teak boards with 1/4" thick maple, then we ripped battens that were 3/8" thick and 2 1/4" wide from those, giving us a maple strip already bonded to the teak. Bonding the two pieces together on a flat table first certainly helped, but they were still far from straight. To eliminate the last of the crookedyness, we laid out the teak/maple slats in the pattern/order as we were going to bond them to the plywood substrate, then we used bar-clamps to squeeze them all together tight, we then put down a strip of 3M fiberglass-reinforced packing-tape (very strong and very stiff stuff) across the wood-slats spaced every few inches. Once the tape was down and carefully rubbed on, we could lift the whole thing, and coat the bottom and sides of each individual slat as we progressively "rolled" them into place, once the whole "sheet" of slats was down, we assembled the processing-stack and the vacuum-bag. However, we had a few issues along the way, (or "opportunities to gain experience" as I like call them) for one, the packing tape didn't stick all that well to the teak, and on the first panel we almost had the slats fall off the tape before we could get them into place, we rectified this problem by alternating the packing tape strips with strips of really gooey tape that was very stretchy but kept the pieces together during glue-up. The right types of tape and liberal application of some thoroughly foul language seemed to do the trick. And that, at long last, is the moral of the story and the reason I used staples instead of tape for the birdsmouth, but I suppose you could use a band of fiberglass cloth and put a dab of epoxy on every slat if you want to avoid the staple-marks.

Yokebutt.

 

And of course, thank you both very much for elucidating the meaning of "swallowtail" to my rather dense and prejudiced mind.

Yokebutt.

 

Turned into quite an amazing thread yokebutt. Don't think for a minute that PAR didn't straighten me out also. I wouldn't have thought about a 12-1 taper on those fingers; But it sure makes sense. Unbeleiveable amount of information....I'll be saving this one.
I was never concerned about building a 25 ft. mast using these techniques but 36 ft. has me wondering. But! If everything does go to heck in a basket....... We do know a builder with a 40ft.bed that can do an 8" diameter right cyclops!!!!

Thanks Everyone
Phil

 

AAAHHH, UUMMMM. No problem. Just remove the roots and wash the dirt off the rest. How long does it take to dry a whole tree without stress cracks? 4 score and 7 years ago our

 

Having just built a 26'er to replace the aluminum one that got bent (it's 19 oz. lighter too) I'd have to say a 36' stick, as a first attempt in mast making, is quite ambitious.

The method has a number of posts on this and other forums. You'd be well advised to do a search for them. With careful planning and lots of dry runs before the glue hits the staves, you can do it. Personally, I'd want a boom under my belt (hint) before I dug into a stick this length.

A 10" diameter pine tree cut down, not de-barked, heavily coated in oil, covered up and rolled 180 degrees every other month will be ready to use in a year, and shouldn't check to badly. Dry it faster in a solar kiln, maybe 3 - 6 months, depending on where you live.