Wow, great idea guys!
I have an idea for UWH playing ground, that could be mounted on the spot, and put into sea or lake. I played arround with different concepts and came to few conclusions in order to make it successfull.

1. Playing ground should be able to last a significant number of years (15+), to excuse its cost.
2. P.g. should be made of materials that can susstain all of the sea water influences.
3. P.g. should be light enough, and designed in such a way, that it can be transported with single truck, and mounted together on the beach in few hours by team of 20 players.

Playing ground can be made in 3 different ways, regarding the buoyancy. Positive, negative or neutral. Becouse of the advantages for easy moving it on the water, and easy instalation, it would be best to have it just slightly positive in the sea. Concrete anchors (moorings) on the sides and under the playing area, would secure it in place. The concrete anchors would be the only part, that would stay underwater for good. Aditional heavy-duty buoys mounted on the sides would make it more stable. Sinking of the playing area would be done from the boat one side at the time, using chain pulley between playing area, anchor and the boat. This would also be used to change the depth of the playing area.
It sounds like I'm dreaming, but in fact its not that hard to make it so. I have lots of experiance in salvage, and I think this way is do-able, but with a challange.

I'm stuck at other problems such as materials and how to make it rigit enough. This would require experimenting. The best way to do it, would be to try varius ideas on a smaller scale model, let say 30 m2. thats little over 5m x 5m, and a scale of 1:10 of the usable field. It would provide proving ground for most of the problems ahead. I was stuck some time, as to what prime material should be used in construction of the playing area, and it seems like I just may have found it.

Now, the part where reallity strikes. Money. Even for the experimenting on the scale model, it would take some serius money to make it work. I would put out the money myself, if it was for full scale workable playing ground, and some "promises" of the future money return from its use. Also, for such a project I would need help... and lots of it. These are the reasons, why I havent moved this project from "idea" stage until now.

Anyone out there?

It would be great, to have tournaments and training camps on the sunny beaches, now wouldn't it, eh?