Originally Posted by
Stanwell
Call me old-fashioned, but in my day of dealing with such things, there was a slight difference between a 'seaplane' and a 'flying-boat'.
A 'seaplane' was a landplane that had been adapted for water-based work - i.e., fitted with floats (call it a float-plane, if you like).
A 'flying-boat' was an aircraft that hat been designed from the outset to use its floating and planing 'hull' for take-off and alighting.
Of course, an amphibian aircraft can be based on either of the above.
The Martin Mars, for example, is a flying-boat (or was, the last time I heard).
Difference between Brit and US usage. In this case, the US usage seems preferable to me (Brit though I be) as making the distinctions clearer.