Replacing Traditional Wood Masts with Alloy

[chris95040]

Originally Posted by SV Windrush II

When the boat is being knocked around in the swell and it is blowing any more than 20 knots, the mast is experiencing bending and shear stress. It is experiencing compression but not as much as the other two. Here is why.

If your mast was experiencing more "bending" stress than the huge compression loads it sees, it would bend.

Have you ever lifted a mast on one end? Its surprising, and illuminating, how wiggly they are. The reason it stays straight on your boat is because something other than itself is handing those "bending" loads, namely, the transfer of that force into tension in the shrouds and compressive loads on the mast.

Imagine grabbing your boat by the masthead and heeling it over. Big compression at the mast step, big tension in the shrouds. Agree?

Now take the shrouds away and do that. The mast is going to bend and snap before the boat gets very far. So obviously the mast is being protected from those "bending loads" when the rig is assembled.

I suspect Jim Cate is right, that this is just semantics and our collective misnaming of forces.. And its further complicated by the fact that a wiggly column's compression loads at some point want to turn into bending (and if not constrained by other means, like standing rigging, turn rapidly into buckling failure..)

[SV Windrush II]

Originally Posted by chris95040

If your mast was experiencing more "bending" stress than the huge compression loads it sees, it would bend.

Have you ever lifted a mast on one end? Its surprising, and illuminating, how wiggly they are. The reason it stays straight on your boat is because something other than itself is handing those "bending" loads, namely, the transfer of that force into tension in the shrouds and compressive loads on the mast.

Imagine grabbing your boat by the masthead and heeling it over. Big compression at the mast step, big tension in the shrouds. Agree?

Now take the shrouds away and do that. The mast is going to bend and snap before the boat gets very far. So obviously the mast is being protected from those "bending loads" when the rig is assembled.

I suspect Jim Cate is right, that this is just semantics and our collective misnaming of forces.. And its further complicated by the fact that a wiggly column's compression loads at some point want to turn into bending (and if not constrained by other means, like standing rigging, turn rapidly into buckling failure..)

Yes I think we just have different ways of explaining it, and my engineering mind is to complicated