Box Mast Fears

Ferro cement is a reasonably accepted building material in some parts of the world, but in the USA, it has a pretty bad reputation. There are a few valid and a few not so valid reasons for this, which you likely know already.

In the USA, it will have the lowest resale value of all the building materials and is the most difficult to survey accurately or completely.

If the boat was built by Windship Limited, then your value goes up a touch, if the buyer is aware of the quality of their hulls, but other wise, it's white elephant that's very difficult to sell. The same is true of Jay Benford designs, built to his plans.

 

Internal halliards aren't a good idea, better to keep the mast weathertight. Internal wiring is commonly installed.

Tang fasteners are usually bolted with a compression tube right through the mast and internal block, the question of the internal blocking causing a stress raiser really depends on the wall thickness relative to the section size. A thick wall and I don't think its going to be an issue. But simple to Cut an intersecting V shape in both directions (fore-n-aft and side to side) in the blocking. I used to see very large masts made like this a few decades ago, Oregon was the preffered timber here.
Wooden masts can be very durable and strong, surprisingly so if you can source the timber.

 

No, I'm not to worried about those issues. Just concerned about the structural. It's a little nerve racking contimplating building your own masts.

C.

 

Since its been mentioned....two sidewalls are 1 5/8", the other are 1 1/4".

 

Three foot by two inch wide strips of inner tube make great gluing clamps. Bicycle inner tubes also work, and most bike shops have a garbage can full of them, free for the taking. Don't put too many on or you will crush the wood.
Brent

 

Build a short section first using cheap materials. You can establish methods, jigs etc that suit you and get a heads up on the problems.