Go with running backstays ....
They are a royal pain in the ass as they need to be readjusted on each
tack BUT the wide base angle (distance from the bottom of the mast to
the attachment point on deck) is large so that the mechanical
efficiency is much more efficient (in comparison to fixed intermediate
stays), can use less strong tackle & wire/line, etc.
The 'nice' thing about runners is that they can be slacked and stored
on either the cap shroud or the lower aft stays when not needed.

With fixed intermediate stays the base angle is too small (the
intercept angle of the stay with the mast) to be of any significant
structural support strength, etc. needing *humongous* strength in the
deck/base and significantly stronger 'wire' than a runner. A fixed
intermediate stay add unecessary 'weight aloft', doesnt do a good
structural job (because of the low interc ept angle with the mast
attachement).
Its all about the 'trigonometry' of the attachment points. and the huge
forces generated by the small intercept angles.
Choose Runners if possible inspite of their being a PITA
;-)


In article , Len
wrote:

I want to install a cutter-stay and two back stays on my 50ft alu
sloop, 1) to add a cutter-jib to my sailing options and 2) to stop the
annoying pumping-motion of my mast.

So my options a

1) Running backstays, which are relatively hard to install reason why
I would prefer:

2) Fixed backstays, to be installed on the existing puttings of the
lower stays and the other end on the exsisting mount of the
intermediates. When fixed like that, there will "room voor the boom"
on downwind courses.

Problem is the very small angle the fixed backstays will make compared
to the mast. They will be fixed to puttings one meter before the mast.
The other end will be mounted 14 meter high in the mast.

What do you think about the forces such an installation will cause
when using a cutter stay in heavy weather?

Regards, Len.