Sizing a panting stay

[Brion Toss]

Hi,
This is a tie rod, whose function is to hold the deck down, primarily from the result of compression by the shrouds, but also against upward pull from mast-base deck blocks. It is only needed with keel-stepped masts, as the mast itself performs these functions with deck-stepped masts.
The load on this tie rod (which, by the way, is very, very rarely called a panting stay) varies with the angles of the shrouds and the stiffness of the house and deck. The load can be significant, but from the dimensions you give, the breaks likely had more to do with materials quality than stresses. Corrosion might also have been a contributing factor. Note that the rod does not need to go into the bilge; it can also attach to the mast (see the Rigger's Apprentice).
Fair leads,
Brion Toss

[Svinshallah]

I'm positive the two breaks were due to corrosion. I replaced the broken stay with a 1/2" turnbuckle with 1/2" clevis pins at each end and 5/16" compact strand wire. My specific question was based on the fact that of the several versions of this stay that I've looked at in other boats, all but one used a solid rod that seemed much stronger than the turnbuckles or attachment points. I was curious why and what was likely to be the weak point.

[Brion Toss]

Hi again,
Aesthetics might play a part, but I suspect that the biggest reason is that it is cheap and easy to thread the ends of a rod, compared to terminating a wire. The rod termination weakens the material, but the material is quite strong.
Fair leads,
Brion Toss

[Svinshallah]

I'm positive the two breaks were due to corrosion. I replaced the broken stay with a 1/2" turnbuckle with 1/2" clevis pins at each end and 5/16" compact strand wire. My specific question was based on the fact that of the several versions of this stay that I've looked at in other boats, all but one used a solid rod that seemed much stronger than the turnbuckles or attachment points. I was curious why and what was likely to be the weak point.