Did you look at lockitron: https://lockitron.com/preorder ? I'm not exactly sure it would fit your need but it seems close event if you might need an extra app/website for people to "book" the kayak?
I think that's how some airbnb hosts give access to their flat without having to meet you in person. At least I've seen it advertised during my last research for an airbnb booking.
Thanks koopajah. Lockitron may be the best solution out there. I was hoping for a padlock that did pretty much the same thing, but with some tweaks I might be able to make the lockitron work for my needs. Perhaps using it in a metal box with a key to the shared kayak storage shed inside.
I think that's how some airbnb hosts give access to their flat without having to meet you in person. At least I've seen it advertised during my last research for an airbnb booking.