: My Mariner-style running deckline got low marks in my IDW since there was too
: much slack. The "preferred" decklines had attachment points
: every 2 or 3 feet so there was a lot less deflection when a swimmer
: grabbed it.

"too much slack"?? for what?. When dragging the boat across your lap it's exactly in the center with NO slack when pulling in the direction of the length of the boat. Most of the deck lines on commercial boats are so tight you can't even get a grip on them, especially with recessed fittings. Like you say it makes a LOT more sense to be able to jump(flail?) out of the boat in the surf and grab that rope and toggle while pulling it up the beach before a wave gets it, and that slack gives some clue that you're about to have your fingers pulled off instead of snug little lines. It doesn't give a big handhold for conventional assisted rescues but after seeing big guys rip deckhardware off that's ok by me.
: If you use it as a towline, do you feel you can predictably and quickly
: release it in an emergency?
No, it's definately a last resort type of item, but simply having a 20ft+ length of reasonably thick (1/4-5/16") floating rope that's always accesible is too useful to ignore. I mean, you get out of your kayak, undue the line at the cleat and tie the line that leads through the U-bolt at the bow onto something. Instant painter. You get to a takeout and someone doesn't have enough tie down straps, there it is. I just haven't figured a way to attach cleats onto the deck in front of the coaming in a way that isn't obtrusive like the recessed Mariner deck. That right there is enough to get me to make a strip boat. cheers
-Lee