I wasn't the one who jailed him but; I usually just provide players with a warning (not a staff warning) and tell them why it's not really a good idea to use it at start since it can cause lag for some players, and that there are other places for them to use it.

The only time I normally give a staff warning is when players continue to use the kayaks even after given advice. After all, it is disrupting game-play for some players near start due to the lag. That's how I would handle the situation.

However, if your friend believes his jail was unfair - he can submit a ticket to http://support.toonslab.com/