Issues with synthetic rigging?

[Brion Toss]

Hello all,
We are in the process of returning to a world where sailors are a living part of their rigs, responsible for design and fabrication, as well as maintenance and use. Part of that process requires familiarizing ourselves with the assorted materials, and the interactions thereof. The expansion issue being discussed here is a piece of that.
As John notes, the pretension required for a (proper) tune with wire masks differences in expansion rates for aluminum and steel. But if you put a tension gauge on the wire on a cold day, and then a warm one, I think you'll be surprised at the difference. In the Northwest, we can use this to our advantage, as the colder days usually have higher windspeeds.
With Spectra, very little pretension is normally needed, so there's less "travel" needed for the rigging to go slack. This might mean more frequent or seasonal adjustment, and it might mean finding an average pretension -- under the "creep" level -- to tune to.
As for longevity, it looks like uncovered Spectra will last at least as long, safely, as stainless in the same climate. Covered Spectra, which costs about 40% more and is more difficult to splice, might still end up being long-term cheaper, as it will basically be immortal. That's why I'm recommending it to cruisers who expect to be in the Tropics for any length of time. Might make a difference in resale value, too. And even with the extra cover weight, it's still lighter than wire.
Fair leads,
Brion Toss