[cwa]

Ben,

You could use 6" aluminum pipe as a mast.
That is what I am using for my boat.
Doing a splice is rather easy.
The wall thickness is a little more than the 3/16" you were looking for as it is over 1/4".
You will have the same diameter for the length you want.
I'm doing 44 feet so there will be two splices for me to get that length.

De,

Nice to see your website about TAZ.
Evan had shown us your boat as an example of his work before starting on ours.
You could consider an aluminum pipe mast as well and just shim the butt end to go into the tabernacle with a tight fit.
Aluminum pipe is very inexpensive in Canada and that helps with the budget.
Hope to meet you this coming summer when we have Evan do a little more to our boat.
Are you still at Newcastle?

Carl