Its an old aircraft hangar which used to be used for seaplanes. Its now run by Hants CC and contains a climbing wall, ski slope & velothingy (where racing bikes go round & round in circles).
I think it's the old Sunderland hangar. I was looking across at it one day and lo and behold a Sunderland emerged from it and taxied into the Solent. It was fairly busy and I said to my wife that no way can it take off. It did and it was an amazing sight.
Slightly differant, came across a photo last week taken in the 50's entering Cowes of the Princess flying boats on the slip, still think it was a sad sight.
The river Rance next to St Malo in France has an area set aside for flying boats to land on. I've never seen one land there though. Perhaps they forgot to amend the chart since the 1950s
I recall the forest fires north of Hanover in 1976(?) when they got dangerously close to a major chemical & arms dump. I was at a German air base at the time on the other side of town and they used a whole variety of planes to dump on the fire including scoop it up from a lake/sea type ones from france. Eventually the wind changed and that put it out but it was getting close. The brit army used every avaiable vehicle to shift the stuff out of the dump including vehicles with no brakes, only one gear, no clutch etc. You name it they were parked on the base!
I remember flying into Quebec airport in the early 1970's and seeing 20-30 of these lovely yellow Catalina flying boats all lined up. Don't know what they were used for but it was a most impressive sight.
Rule 18(e)
A seaplane on the water shall, in general, keep well clear of all vessels and avoid impeding their navigation. In circumstances, however, where risk of collision exists, she shall comply with the Rules of this Part.
In other words, seaplanes come right at the bottom of the pecking order:
Not under command
Restricted in ability to manoeuvre
Engaged in fishing
Sailing
Power driven
Seaplane on the water.
Interesting, wouldn't like to be the one shouting "Starboard" though. Nearly went past the place today on my first ever sail in Southampton Water, aren't those ferries quick!