Best glue for bird's mouth mast?

[davidrparker]

What would folks here reccomend as the best glue to use in assembling a bird's mouth mast? I have read both that epoxy is the stuff to use and also that this is not the place for epoxy.

Thanks, David

[Thorne]

Size, material, and use of mast will determine a lot.

I tried gluing up a simple mast of 2 2x4's with the Weldwood resin glue, but didn't get either (or both) the clamping pressure or temps correct, and had to re-glue the lower 1/3 of the mast by cleaning out the glueline and using epoxy.
http://www.dap.com/images/products/00203t.jpg

Let's see what the more experienced folks say, but I'd recommend epoxy for most small-boat masts that are not supposed to flex a lot.

[paladin]

I would say that it depends on mast size and use.....the mast is gonna flex.....so you need an adhesive that will flex at the same rate as the wood......the only epoxy that I am aware of formulated specifically for that purpose is T-88, now sold by System Three, developed for aircraft spars...

[Clinton B Chase]

For a lug sail spars, which you do not want to flex even a little bit, then epoxy will be best for stiffness. You especially don't want the yard and mast to bend so that'd be the place to use epoxy for stiffness. And there are flexible epoxies and non flexible ones. I don't know a lot here, but WEST seems to give a stiff glue joint compared to other epoxies.

Cheers,
Clint

[paladin]

Unfortunately...wood flexes.....no matter how stiff you build it, it will flex....if the glue line is more rigid than the wood you will in effect get something remotely described as "rolling shear"......the wood gives ever so slightly, but the glue doesn't....eventually destroying the join.....it is best, IMHO, to have the glue with the same flex characteristics as the material being joined. If you want to stiffen the member, use splints....in this case, use the proper epoxy and lay carbon fibre ribbons between the joins.....

[Bob Smalser]

http://pic20.picturetrail.com/VOL12/1104763/7099973/92113916.jpg

The major glue characteristics required for birdsmouth construction are long open times, ability to fill gaps, good adhesion at relatively low clamping pressures, and (usually) ability to cure outdoors in cool temperatures.

That sure sounds like marine epoxy applied with a slow hardener and high-adhesive thickener to me. I'd only consider resorcinol or UF resin in a box section mast I could get more serious clamps on, and then only when I could get the joints to 70 degrees for 12 hours.

[davidrparker]

Good points, what would you consider a good high adhesive thickner? I was mainly concerned about the epoxy kicking off on me before I was ready but as cooler weather approaches that will become less of a concern. BTW, this is for my Macgregor canoe. the largest diameter is shown on the plans as 2", which is for the main mast.

[Clinton B Chase]

No problem with open time in a mast that size...I am using 406 with wood flour 50/50 these days and loving the consistency. (You can also use a 406/403 mix 50/50...a good all around glueing mix) If you are confident in your joints go with a catsup consistency/mayonaisse conistency if you are in doubt. Or use System Three Gel Magic in the tubes (load in the caulk gun) and dispense with a mixing tip right into the groves in the staves...perfect results all the time. This will give you the gap filling/low clamp pressure forgiveness as well as the flexibility and stiffness you need for the mast...you are doing balanced lug rig masts so you want a very stiff spar. Be sure to sight the length of the mast after you have snugged up on all the hose clamps...you can easily get a curve in the spar. Clean up with denatured alcohol so you can enjoy shaving off those edges with out dullling the blade with cured epoxy. Don't forget to glue plugs into the ends and perhaps a plug where you might have some hardware mounted on the mast (but prob. not nec. for a little boat like yours).

Cheers,
Clint

Cheers,
Clint

[Boatmik]

Howdy,

The join will be so thin relative to the size of the timber structure the stiffness of the glue will be negligible. All plastic based glues have very similar stiffness at any rate.

Gap filling is the single most important property - and I would steer well clear of prethickened epoxy glues. Buy a quality resin system West, Sys3 or any ones well regarded for boatbuilding and add the right powder. Cheap brands are generally a lot weaker than the established ones (One university here did some tests of about 16 brands and the three premium brands were WAY ahead and the cheap ones were very poor - maybe 1/3 of the strength for the tests that were done (tensile, shear and energy to fracture)

While I agree with Clinton about the masts above - lug masts need to be stiff, but not so stiff that there is excessive weight. Other rigs can allow a greater degree of flexibility in the mast unless there is a jib flown without the mast being supported by side stays - which is generally a poor performance option anyhow.

Despite what happens with the mast there are very big advantages in the yard (or gaff) and to a smaller extent the boom being flexible.

This is the biggest single innovation for conventional racing boats - from the Star when it went bermudan in 1929 to almost all sailing boats today is using controlled spar bend to make the boats easier to sail and reduce the need for reefing.

There is no reason that it cannot be utilised for a more traditionally built boat also.

The advantage of getting the RIGHT amount of bend is that the sail will automatically flatten out in a gust as the yard (and the boom to a smaller extent - but SPRIT booms must have NONE) bend which reduces power to a great extent, then when the gust passes the spars will straighten and you have full power again.

The difference in handling is great - the boat accelerates cleanly in gusts and keeps trucking in the lulls. In other words - you can carry a much bigger sail area without suffering any disbenefit.

There is some general information about this topic here
http://www.storerboatplans.com/Faq/tradrigperformance.html

The important thing is the designer has to get the stiffness of the spars right - if they are too stiff the boat will become less controllable in gusts - if they are too flexible the boat will lack power in moderate breezes or if it has to punch its way into a chop.

A fellow contacted me a year or so ago to tell me that my Goat Island Skiff design was impossible to sail. He had made a number of changes to the hull and rig - but the biggest problem was he had replace the timber spars designed for the boat with some heavy walled Aluminium tubes - way overspecified in terms of stiffness.

When he replaced them with correctly proportioned timber spars in the plans it behaved normally.

Best wishes
Michael

[David G]

Good points, what would you consider a good high adhesive thickner? I was mainly concerned about the epoxy kicking off on me before I was ready but as cooler weather approaches that will become less of a concern. BTW, this is for my Macgregor canoe. the largest diameter is shown on the plans as 2", which is for the main mast.


I don't know whether you're following a designers specification, or winging it. If the latter, I'm not sure I'd be thinking about a birdsmouth for such a small stick. It can be done, but it's lots of extra work & complication for a very small weight gain compared to solid sticks of that diameter. Even if the former, I'd be quizzing them on the necessity for the birdsmouth. OTOH, if you're just looking for an excuse to build your first birdsmouth project, never mind me... just carry on, and have fun<g>

If you do go birdsmouth, the two most commonly recommended adhesives are resorcinol and epoxy. Resorcinol is the one that's been around the longest. As Mr. Smalzer noted, it does require tighter joints, higher clamping pressures, and higher temperatures to cure than epoxy. If all of those are provided, along with sufficent glue & adequate cure time - it will last. For example: I'm working on a project now replacing a Frisco Flyer mast - which is a hollow rectangle. Cheoy Lee built the original stick in 1964 with resorcinol, and it lasted until recently - when the riggers dropped it while unstepping for a refit. Turns out the glue joints were failing anyway, but it had lasted over 40 years at that point.

The owner & I are discussing whether to build the new one with epoxy or resorcinol. I have no problem with whichever one he decides. I've used both, though I have far more experience with epoxy. Mostly I've used West System - since it first came out. But lately I've used mostly RAKA. I would consider using T-88 from System3, or G-Flex from West - but I'd have to spend some time talking to their tech folks before I felt comfortable going that route.

Another possibility: Titebond III. A well-known local builder recommended it to the owner for his F.Flyer mast. I haven't spoken to him, as the owner rejected the notion. I imagine the reasoning went something like: strong; perfectly waterproof; remains slightly flexible when cured; easy; inexpensive; long open times; less gooey; less toxic. My two main concerns would be repairability & lack of track record.

"I was thrown out of college for cheating on the metaphysics exam. I looked into the soul of the boy sitting next to me" -- Woody Allen

[Tom Lathrop]

The one thing that cannot be avoided in assembling a birdsmouth spar is long assembly time needed to get the glue on all those joints and the ability to move the pieces around into alignment. This requires a glue with a long set up time. Since the joints are not likely to be really tight and high clamping pressure is impossible to get in any normal situation, epoxy is the clear choice here. A slightly flexible one would be the choice but successful ones have been built with whatever is on the shelf.

[paladin]

My recommendation for using Schindlers (now System Three T-88) is that it meets all the requirements, does not need fillers, is 1:1 mix, and if you do it in the cool of an evening, you will have plenty of assembly time.......

[Bob Smalser]

Another possibility: Titebond III. A well-known local builder recommended it to the owner for his F.Flyer mast. I haven't spoken to him, as the owner rejected the notion. I imagine the reasoning went something like: strong; perfectly waterproof; remains slightly flexible when cured; easy; inexpensive; long open times; less gooey; less toxic. My two main concerns would be repairability & lack of track record.



Go to the Franklin site and even they will tell you it creeps under load, won't fill gaps and isn't recommended for high-stress applications. Moreover, anyone who says it has long open times sounds like someone who either lives above the Arctic Circle or hasn't used much glue of any kind. An extremely poor choice for your application, without even considering repairability or track record.

[sv Lorelei]

What about PL Premium? I've been using this in laminating ribs and find that it's much more conveniant to work with out of the tube than epoxy mixed in small batches, has a long cure time and appears to bond well, and is consistent. Any disadvantages?

[Tom Lathrop]

My recommendation for using Schindlers (now System Three T-88) is that it meets all the requirements, does not need fillers, is 1:1 mix, and if you do it in the cool of an evening, you will have plenty of assembly time.......

Chuck, You must remember Jerry Schindler and the Cleveland Boatbuilders group. I bought some of Jerry's T88 in the early 70's and found it very strong and workable at lower temperature than the others available at that time. The problem I had with it was the very viscous nature that made it difficult to measure in small quantities and difficult to stir for mixing. Have used only a little since then. Is it still like I describe?

I much prefer the easy handling of the low viscosity mixes of thixotropic glue. I second Bob's note about Titebond ll or lll. I doubt that it would be possible to ever get a birds mouth mast assembled with it in the first place so creep would never be an issue. Set up, or tack time is far too short for such a project.

[Bob Smalser]

What about PL Premium?

Open time. Skins over rather quickly in warm weather. And no track record; I'll let others do the experimenting, thanks.

[kc8pql]

The major glue characteristics required for birdsmouth construction are long open times, ability to fill gaps, good adhesion at relatively low clamping pressures, and (usually) ability to cure outdoors in cool temperatures.

That sure sounds like marine epoxy applied with a slow hardener and high-adhesive thickener to me.

I came to the same conclusion. I used System Three, slow hardner and high density filler on well primed joints. Lots of extra hands helps too.

http://i9.tinypic.com/81k6dk6.jpg

http://i17.tinypic.com/6l41gtg.jpg

[Gary E]

After all that work, cutting, shaping, glue, etc etc...EXPENSE ???
and are you going to make it round after all that??? more $$ and time

Are you any better off with this or just cutting down a suitable size TREE??? it's allready round...

[George Schuld]

Gary E,

I know what you mean. Birds mouth spars are surely not the easiest spars to make. But for spars for racing boats that require round hollow sections they are IMHO opinion a very cost effective option to get a quality race spar. I've built several dozen Sitka Spruce racing spars over the years and have used quite a few methods. For a local racing class (A-cats ...barnegatbayacat.com) I have built 4 49ft round (birds mouth) masts that are 6" diameter tapering to 4". For these spars we have made many purpose built jigs, custom shoed hand planes, and one pretty nifty turning lathe capable of turning spars up to 70ft. The spar lathe really helps out. We have custom built all the spars for the Bull and Bear Sandbaggers (very cool boats) and were able to vacuum bag unidirectional carbon fiber to the inside surfaces of all the staves for them to make the spars stiffer and stronger. They work great.
As far as the mentions of whether epoxy is suitable to this type of spar construction, I say absolutely. We use West System exclusively and bending spars does not cause a problem. For example, for the Sandbaggers, we built setting out poles for the jibs. They are 28ft long and are 2 3/4" in diameter in the middle tapering to 1 7/8" at the ends with a 5/8" walls. With no carbon added to these. During an unofficial "test", we were able to bend one of them in a nearly perfect u shape (with great force needed ...don't ask!) The seams were perfect, didn't even hurt the varnish. Nearly all the racing spars that we have built are regularly pushed very hard on the race courses, and we have yet to have a single glue joint failure of any kind and certainly no one has been able to break one of our spars yet! Not that I consider that a challenge or anything.

If anyone has any questions about the process let me know.