a question about gluing

Kindly forgive what must be a rather simple question, but why
are wooden masts glued rather than fastened. I've consulted
Chapelle and he does not really treat this subject other than
explaining the gluing process.

 

Becouse it's much better in many ways.. stronger.. lighter.. long lasting etc

 

If you look at the publication dates of Chappelle's books they pre-date the availability of reliable waterproof glues.In spite of this,glue was used.The more relevant consideration for masts is that a glue bond is uniformly strong.A line of fasteners is strong at the points where the fasteners are located and will become weaker after numerous cyclic loads are applied.It is also quite difficult to shape the mast if there are fasteners present.If you are building a replica large ship from the mid nineteenth century or earlier different considerations apply.

 

With the exception of through fasteners (nut and bolt) a good glue will yield several advantages. A prime consideration is weight aloft. After you count up hundreds of fasteners on a lengthy built up mast, the weight will make you sweat in the first real blow the stick sees. Fastener arrangement, as has been mentioned, can cause a host of issue, like trying to screw a sail track down and having internal fasteners get in the way. Hard points and stress risers are another issue. the fasteners create a localize clamping force that rapidly decreases as you get further from the fastener. Under bending loads this can place surrounding wood under undue stress, causing localized fiber failures. This can be commonly seen as compression around the fastener heads or distortions in the general area, both weakening the mast.

Applied properly, glues can generate a uniform bond between pieces, stronger then the fibers themselves. This makes a homogeneous column, one that will react uniformly to load, not the dictates of fastener spacing.

Some masts, box section in particular, will have small brads to hold the stave's in place while the glue cures. These offer little to no structural advantage other then initial alignment.

Chapelle used and wrote about truly waterproof glues, including resorcinol, plastic resin, which he was fond of and epoxy, which he wasn't completely convinced of yet. He passed in 1972 and was well aware of the "new fangled" goo's.

 

Herreshoff was using "plastic" glue for spars in the 1920's already. Chapelle's book is of much later vintage.