Hi Ralph: Congratulations on catching such a fun assignment! Here's a suggestion for the documentation part of the open space on a beach: Something I've done often is to create a master supply of clipboards for each convener to take to their sessions and return to the Clipboard Depot.
Clipboards give people a hard surface to write on. A pen can be tied to the metal ring with a string or wire. A supply of paper can held by the clip. The paper can be pre-formatted into a template with the information you require about each group. You could even offer one for each person - a manual portable laptop, if you will. Come to think of it, I suppose the completed sheets could be posted on a vollyball net (just for fun, if nothing else) with small metal clips. For the community bulletin board, should you want to go with a wall, consider erecting a snowfence. The material, pegged to steel uprights, is inexpensive and designed to quickly and cheaply span long distances. Don't forget your sun tan lotion and shades! Best, Jay Vogt