Thank you everyone for your insights. I think we'll be getting our hands on the 32" spar for this project. Once it's in the yard I'll be able to start fashioning the receiving cup for the keel step and properly build up the partners. 

Hi Adam,

assuming a sail area of about 300 square feet with a center of area about 18 feet above the water then the righting moment for the rig at 20 miles per hour wind is about 5400 foot pounds. The strength of the smaller of the masts, using a strength for the aluminium of 20,000 pounds per square inch, will resist a moment of over 20,000 foot pounds. The longer mast is not quite as strong but both would give a safety factor of above 3 which is more than adequate for most purposes.

Arne has a different calculation method, but we usually come up with pretty close results.

All the best, David.

The most critical dimension for strength consideration is the diameter of the mast. What are the diameters of the masts under consideration? This will allow some rough calculations to be made as to strength and hence suitability for your purpose.

Adam,

Do you know what size of Nonsuch these were fitted to? I can't find a luff length for the Nonsuch 22, but for the 26, it was 41ft, and it seems unlikely that either of the masts under consideration was originally fitted to a boat of similar size and righting moment to yours. A mast for the Nonsuch 22 would not be stiff and strong enough, I fear.

Alright - mast question for the subject matter experts - especially Arne but anyone else with build experience.

Two masts: One 32' the other 36' have been found. I only need 31 feet.

They are aluminum extrusions. Both formerly from Nonsuch's.

Both are sleeved.

32' thickness tapers from 7mm to 5m

36' thickness tapers from 5mm to 4mm

The challenges:

One extrusion has had holes tapped into it for a sail track. Does this pose a structural issue?

The other - where the top and bottom sections meet has a bolt that protrudes. I could ... in theory ensure that the bolt that protrudes has its profile reduced, and that a small fairing be glassed over it to ensure that the parrels or battens slide over it. As it is - there's a real risk of it snagging either or both.

These are the best two candidates to come along in over a year's search. Everyone seems to be squirreling away their lamp posts. OR in the case of the Southern Ontario aluminum extrusion industry, they will not produce extrusions unless you are ordering in batches of 10,000.

And before the suggestions flow about a wooden mast, that option is my very very last resort as I'm fully aware of my limits as a carpenter.