@Demonstrata
You have to shoot the second cannon on the other boat, in a direct line between you and the moving boat. I will change it to make it more clear.
Thank you for the tip

Hole 16 seems to be broken. 1) it's nearly impossible to workout where to go. 2) the actual break... a) if you put the ball into the moving boat, it just goes back and forth infinitely b) you cna run down the clock and you never end the hole, so going back to 1, you wind up in a groundhog loop of shooting the ball anywhere in the hopes that you stumble onto the right target. Turned out it was easier to shoot into a previous cup.