: After the great discussion last week on deck rigging, I popped down to
: Mariner Kayaks and bought some 1/4" nylon line for the
: safety/perimeter line on my Arctic Tern. Nice feel to the line, thick
: enough for a cold hand to grab, one color (white) fits all, but I didn't
: buy enough.

I'm surprised that Mariner sells nylon line. It's plenty strong, but stretches when wet, so it makes poor deck lines

: With Mariner closed on Sunday, I stopped at a West Marine
: store to buy some more line, and was amazed to see lots of other lines to
: consider -- polyester double braid;

This works well and it's reasonably priced.

: Spectra braid

Spectra is very strong and very expensive. Ropes with Spectra sheaths do not hold knots well, as spectra is very slippery material. Many (most?) Spectra ropes have a Spectra core with another material for the sheath. Spectra's one Achille's heel is that it's very heat sensitive and prone to creep (stretch permanently) if it gets hot while under tension. Personally, I don't see any real advantage to Spectra for deck lines.

Braided polypropylene is light weight (it floats), low stretch and reasonably priced, but I have only found a limited selection of it at local boating suppliers. I use it for my tow line, so it will stay at the surface.

: A sailing friend tells me I've seen the tip of the iceberg on ropes and line.
: He advises me to disregard the strength and weight data and get a line
: that is somewhat stiff to keep it from snagging my paddle when I roll, yet
: is flexible enough to tie in knots.

Since your deck lines should not be loose, the flexibility of the rope isn't terribly relevent. Ease of tying knots and knot holding ability is more important.