Just a note of experience: While towing our C-12 w/15 hp in 6' seas/23 kts off the S side of St. Thomas this weekend, the snap link that connected the thimble eye on the tow line to the towing ring failed. It looks like the spring broke. And thus, we noticed our dink going the opposite way of our boat. It was an interesting rescue in those conditions. I ended up diving overboard and jumping into the dink as it as very hard to get the 2 boats side by side at the same level (dink rides side to wind and swell).
I had crew attached a shackle to the tow line and toss me the center part of the tow line, came up close to the stern of the sailboat, then had 100' of float time to attach. Then it came time to get on the bucking transom... good timing and all was done. It was a good drill.
Lessons: No more snap links for convenience. Heavy shackle only. Those conditions were a bit big for towing... sail elsewhere or haul dink.