Hmm, while reading this thread a bit more I get the feeling that the disadvantages of Nylon may not be so clear as I thought. Here's the 4 reasons:
. Nylon absorbs water
, loosing strength (15%) and gaining weight. Polyester does not absorb water and does not loose strength when wet.
2. Internal chafing. This is caused by heat build-up inside the rope. The 12-plait versions might do much better but you still have the water absorption (the more stretch, the more heat build-up inside).
3. External chafing. Polyester is more durable. Sure you can oversize Nylon which you also need to because of reason #1. But that doesn't mean Nylon is better suited for use on a boat.
4. UV damage. They say Nylon is as UV resistant as Polyester, which is BS. We wouldn't need polyester sails
(Dacron = polyester) if that were true. They dare to state this because of a UV resistant coating on the rope. However, that coating will quickly disappear when you use the rope as anchor rode, loosing the UV protection at the same time.
-> New England
Ropes 3-strand Nylon stretches 11% at 20% of breaking load. (http://www.neropes.com/Datasheets/MAR_3S_nylon.pdf
-> New England
Ropes plaited (12-strand) Nylon stretches 2% at 20% of breaking load. (http://www.neropes.com/Datasheets/MAR_MBII.pdf
-> compare the previous numbers with the rule
of thumb figures of Nylon stretches 22-24% and Polyester stretches 15%. Things don't compute.
Anyway, the stretch of Polyester as an anchoring rode is good enough or, if you really want more stretch, use a Nylon snubber on your Polyester anchor rode. Chafing resistance is the BIG reason that more and more select Polyester (but all chain is even better of course).