Boz
Well-Known Member
just a quickie ---- anybody any idea what the metal thickness is likely to be about 5ft from the top of my Westerly Corsair's mast (mast height 48' above the deck and no taper)
Mast metal
- Thread starter Boz
- Start date
Motor_Sailor
Well-Known Member
The wall thickness will be consistent all the way up. It's an extrusion. So you can measure it at an opening at deck level.
Boz
Well-Known Member
Thanks - I hadn't thought of that -dooooh
merlin3688
Well-Known Member
As mentioned if not tapered then the same all the way up, guessing about 6mm, Z Spars section Z701 has been used on the Westerly Corsair however most older boats had a Proctor or Kemp mast. If you are putting in rivets use Monel and 3mm of rivet inside the section.
Motor_Sailor
Well-Known Member
I've never seen an extruded yacht mast with variable wall thickness. Tapered masts have simply had a long 'wedge' cut down each side and then pushed together and welded. The rather crude 'cut and shut' of mast construction. The wall thickness is predicated on the needs of the most highly stressed parts resulting in most of the mast wall thickness being overkill. That's why they're so tolerant of holes, etc, being cut in them.
To get a variable wall thickness mast, they have to be fabricated. The huge racing yachts in the twenties and thirties used this technique with some even built in steel. However extrusions economically spelt the end to this until the Whitbread 60s came along. In their early incarnation, carbon masts were banned on the grounds of cost, so aluminium masts were fabricated with variable thickness parts placed according to some early engineering finite element analysis. They were relatively successful although cost far more than a carbon spar of similar performance. It's not just that carbon is light that makes it good for masts - it's also that the thickness at various parts of the mast can be varied so easily during construction.
Boz
Well-Known Member
Kemp are now Selden, I believe. Looking at the website there is apparently a reference number at the base of the mast which should lead me to the wall thickness if I haven't measured it by then anyway. I had estimated it at 6mm myself by removing a screw and poking about with a straightened paperclip. This sort of ties up with the Selden website....
There seems to be mixed opinions on Monel or Stainless rivets. Either way I'll use Duralac copiuously
