Dacron vs. Polyester
 

Recently had origional halyards and sheets replaced on 1980 Cape Dory 30 cutter. They were 7/16in prestretched dacron,and were replaced with 3/8in Sta-Set polyester. Sail coastal and blue water cruising. What lifetime can be expected compared to the 20+ yrs the origionals? Any maintanence that can extend polyesters' life?

Same, sort of
 

Hello,
First, Dacron is a registered name that DuPont uses for its polyester. By any name, it's polyester, but some people make it better than others. We buy Dacron, as a preference.
Next, what construction was your old line? If 3-strand, you either had filament fibers, in which case the strength would have been close to 6,000lbs., or spun fibers, in which case the strength would have been more like 3,300 lbs. Your new rope has a rated strength of 4,400lbs, so it is either a lot stronger or a lot weaker than what you used to have. It is likely to be less elastic in any event, due to its construction, which brings up the questions: why double-braid; and why the diameter change? Sta-Set-X would have been a better choice for main and jib halyards, at least (3/8" is 5,500lbs, and even less stretch).
As for maintenance, the best thing you can do is to send the halyards down when you are not using them for stretches of time. Occasionally, if they start to look dirty, wash them. No bleach!
Fair leads,
Brion Toss