HD: the positioon of the 'tower' as marked on your map puts it close to the position where I must have seen the 'boat' in '56, whereas I would have thought any 'control' facility would be about 2 miles south at Hythe, mind you I do remember having an RAF chart dated about 1960 (lost long ago regrettably) which showed more than one 'water' airport on Southampton Water (it also showed a land airfield at Ryde on the I.O.W.)