As the plans say, getting the aluminum mast is difficult. I tried the
local Metal Supermarkets, plans say 16' of 2-2.375" .065 wall Al
tubing. All they could get was 2" .125 wall thickness. Considered
using it but it would flop around in the big mast hole so found a
place on internet selling 2.25" .065 wall in 16' length for $109,
other two pieces for the lateen rig will be 12' 2" .o65 wall for $95
each for a total of $299 for each boat......WOW. No idea what
shipping will cost. Any ideas anyone? Should I use the 2" .125 wall
from Metal Supermarkets (essentially free since they owe me money)?

Hi,

just did a few numbers (everything in decimal inches/ sq. / cu. as
appropriate), and assuming the same density of aluminium in each, just
to compare the tubes.:
1.56 oz./cu. in. is just an encyclopedia value for the density of
aluminium (2700Kg/cu. M).
Based on a 16" length.

Recomended tubing:
Diameter 2.375
Outside Radius 1.1875
Outside Area 4.430136515
Wall Thickness 0.065
Inside Radius 1.1225
Inside Area 3.958426378
C/S Area 0.471710137
Volume of 192" 90.56834629
1.56oz/cu. In. 141.2866202
Pounds 8.830413763

Metals Supermarket tubing:
Diameter 2
Outside Radius 1
Outside Area 3.141592654
Wall Thickness 0.125
Inside Radius 0.875
Inside Area 2.405281875
C/S Area 0.736310778
Volume of 192" 141.3716694
1.56oz/cu. In. 220.5398043
Pounds 13.78373777

Someone might check that over - I'm a metric kid, and these ancient
mariner inches, rods, bushels etc. confuse me no end. Alternatively,
I may have just made a hames of the numbers.

Tubing you're suggesting is 55% heavier than the suggested tubing.
It'll also be up pretty high -a 5metre length of this forms the upper
spar of the lateen rig, and it's held up pretty high at the aft end.

Someone more clued in than me could tell you how the difference in
radius and wall thickness would affect strength and stiffness
(stiffness increasing in proportion to square of radius or somthing?).

Generally, the worst place for more weight is up high.

However...

....the building notes are pretty slack when it comes to specifying
tubing for the masts.

You're still within the 2"-2.375" range per the plans.

They suggest everything from irrigation piping to car exhaust
sections.
They also say that if the tubing is too flexible, it can be stiffened
with a baton of wood running along the line of stress (fore-and-aft in
most of the tubes), so there's probably a fair margin of safety in the
measurments.

As usual, it's up to you. I'd hate to say it looks Ok, then have the
rig come down on your head in the first stiff breeze you go out in.

If you you do use the smaller tubing, just shim the mast hole, but
make the shims removable - stick em' in with a few blobs of silicone
on the back so that they'll stay where they are, but can easily be
pried off if required.

Seems you've still got a fair bit of finishing, filling and painting
to do before you need the masts anyway, so I'd keep looking round for
a bit, rather than blast ahead when you could get better stuff.

Regards,

bookieb.