I have swam with the support of a kayaker 5 times. 3 of those times were 10 K swims, another was a 9 mile swim and a swim from Catalina Island to the California coast.
The primary purpose of the kayak support is the safety of the swimmer.
In my 9 mile experience, my escort power boat left both myself and the kayaker in the Tampa Bay 24 mile swim. That is the reason I had to get out after 9 miles, but if it were not for my kayaker, I likely would have gone to shore at sometime before the 9 mile mark.
In my 10 K swims the kayaker has been my guide from start to finish along with providing me with feedings and water. My wife and sons have been my support kayakers for two of those swims and friend for the third one. My wife and sons have been very supportive even when I asked if they knew where they were going. They could see the end I could not. In that swim, one of the swimmers went into a cove and the kayaker could not get them back on course until much effort was made to comunicate that the swimmer was off-course.
In the Catalina to Calfornia Crossing the kayaker was next to the swimmer instead of the escort boat. So the kayaker again provided feedings and guidance, the kayaker made sure that I was not sucked under the boat.
The Role of the kayaker is to provide a safety net, feedings and liquids for the swimmer. Without a kayaker many long swims could not be done.
Animal
When we've started out before dawn, it's always nice to "go to the light" of the kayaker. Also, for longer swims you can't beat the psychological aspect of having someone else along for the fun.
Finally, who else can carry the beer and chips?
One of the reasons I ask is because I thought one of the aspects of open water swimming usually included the swimmer's navigation ability, i.e. the swimmer's ability to maintain the straightest possible line. So I was wondering if a kakay escorter is supposed to help the swimmer stay on line or not?
The kayaker is to lead the swimmer for the longer swims, of say 10 K or more. If a swim is 10 K or less or has buoys that a swimmer can see then there is no need for a kayaker to lead. In the 3 mile swim for the La Jolla Rough Water Swim, there are people on paddle boards. Usually a swimmer will set one up for his or her self. What happens is that a group of like speed swimmers will then follow that paddler, so that sighting as often is lessened.
For my 5.44 mile swim, they require kayak escorts, and I've felt SO much better having someone nearby. It's partly the feed (some races I know have feed stations, but I've never done one of those and am not sure how that would work--I like that I have someone exclusively for me). The swim goes across the Great South Bay, and so there's boat traffic including ferries. It's hugely reassuring that (1) the boat operators know of our swim and the Coast Guard keeps an eye out but (2) having someone right at your side makes for even more safety. Never once in the three times I did that swim did I ever feel unsafe. Nauseated from seasickness, exhausted, wanting to be on land ASAP... but not unsafe!
Primarily, safety, kayakers are within a few feet of a swimmer and can spot trouble early. It's pretty frequent, especially in a short, intense swim like a triathlon, that a kayaker needs to talk a panicky swimmer down so they can finish the swim portion. Some just need a pool noodle tossed, or few minutes rest on the bow of the kayak to recover. On longer swims, we can easily provide nutrition and encouragement without diesel fumes. I think the most important role on long swims is to help the swimmer to not have to sight as often. If the kayaker is always pointing in the desired direction, the swimmer only needs to keep themselves oriented to the kayak.
