[Brian Duff]

Thanks, Brian. I'll have a look at Vectran.
How much does Dyneema creep? Is it just the tiniest bit? And does it ever stop creeping?
Creep varies with load and manufacture of line - but it is not the tiniest bit, its a lot. For instance on runners one size up for a Tayana 55 (3/8" amsteel) they elongate 6" a year, each year (we keep shorteing them, three times now- this fall they will get changed to Dynex Dux which is prestretched so shouldn't creep as much)

Could creep be mitigated by oversizing? Yes , it sure can, but it always creeps, just less at lower percent of load. That is how we deal with the problem when using the Dynex Dux, oversize stuff a bit.

The boat is a Cape George 31 pilot cutter I'm finishing from a bare hull; I'm putting a gaff rig on it rather than a marconi. IF its to be gaff rigged, keel stepped and set up with deadeyes, then Dyneema will likely be fine, as these rigs get a large protion of their strength from the bury in the deck (depending on design) and so shourds that get abit slack wont be the worst thing - I have yet to sail on a gaffer that doesn't have slack rigging on the lee side when loaded up.

Check out the Hampjeden website, and Colligo Marine, and Precourt Marine for more info, or give BRION TOSS a call

more about the rig design will help give you better advice. do you have a drawing ?