Martin P6M Seamaster

[hval]

Jane-Doh,

Seaplanes may be split into two groups; float planes and flying boats. Neither is able to take of in particularly rough weather, in fact the weather needs to be relatively calm. Flying boats are able to take off in rougher weather than sea planes. Sea state/ water state limits the number of days that sea planes may take off; more so than an aircraft taking off from a runway on land.

Floating objects are another hazard

A seaplane during take off has to overcome hydrodynamic forces (water drag is the major part of the forces resisting acceleration). This resistance reaches its peak at a speed of about 27 knots, and just before the floats or hull are placed into a planing attitude. Several factors greatly increase the water drag or resistance; heavy loading of the aircraft or glassy water conditions in which no air bubbles slide under the floats or hull, as they do during a choppy water condition. In extreme cases, the drag may exceed the available thrust and prevent the seaplanes from becoming airborne. This is particularly true when operating in areas with high density altitudes (high elevations/high temperatures) where the engine cannot develop full rated power

For seaplanes, the forces involved in take off are different to land planes. Sea planes have to overcome hydrodynamic forces which require additional power (I think of the water as being “sticky”). These forces increase until the float hull is out of the water or on the stepping plane. Did you know that float planes have two hull designs? One for when the aircraft is sitting in the water/ taxying around and one for when on the stepping plane and taking off.

I am now going to quote from a useful website (Flying Seaplanes): -

The seaplane takeoff may be divided into four distinct phases:
(1) The "displacement" phase (plane sitting there or taxying)
(2) the "hump" or "ploughing" phase, (accelerating for take off)
(3) the "planing" or "on the step" phase, (overcome most hydrodynamic forces, accelerating for take off)
and
(4) the "lift off." This is where the wings produce lift and start to raise the hull from the water.


Take a look at the web site I have linked to. It may answer many of your questions re sea planes.

Sea planes are great, but economically, as passenger aircraft, they were not viable in todays requirements for being on time. As stated above, not only do sea planes have to take in to account the same weather conditions as land planes, but also the added component of sea state.

Hval.