This is what John H. wrote me when i asked him what side up for the aluminium gunter sloop mast (which comes in two pieces):

"I would put the short piece of mast towards the top. At an
engineering level I don't think it makes any difference. But since
the location of the joint influences the bend of the mast under
sailing loads, and the shape of the bend is a tiny bit more ideal for
the sail shape if the joint is up high, I'd put the short piece on
top. "

And so i did :)

Ruud

Anthony,

A properly made scarf joint is stronger than the wood. That is, the wood will break before the glue line does, so it makes no difference where you have it.

That said, the top of the mast has less stress than the bottom (that's why masts can be tapered) in case you want some extra insurance..

Have fun,

Laszlo

There's another thing to consider.  Even though the scarf joint is stronger than the wood, it's not as flexible, especially in one direction.  Most of the flexion on an unstayed mast happens just above the partners so I would orient the mast so the scarf was toward the top and with the sides that show the joint angle (as opposed to the straight seam) fore and aft.  My $0.02.

   My vote is with Lazlo. It doesn't matter where you put your scarfs if your joints are good.

Apparently, I did everything wrong. My scarf joint starts about three feet up the mast (and continues for another foot or so). It is not oriented optimally. And to make things worse, when I was trimming the base of the mast with my hand-held circular saw, I cut out a small divot that I later had to glue back in to make the dimensions work.

The mast looks good. None of these joints is visually offensive. And I have sailed the boat (unreefed) in very challenging conditions. I'm talking about 20 - 30 mph gusts. It flies. And the mast has held up. Knock wood!