Here's a game I used for single handed dinghies - Optimists in this case. Each boat has a balloon attached to the back on about 2m of string (a loop in the end of the string dropped over the tiller is the quickest way to attach them). An area sized appropriately for the number of boats is designated by four buoys - a rough square - and every one has to keep within this space. At the signal the participants have to try and pop everyone else's balloon. Last one left with an inflated balloon is the winner! Rules are - you cannot leave the designated area and may not shorten your string by retrieving it. The length of string helps reduce the risk of collisions.