Unlike landplane operations at
airports, seaplane operations
are often conducted on water areas at which other
activities are permitted. Therefore, the seaplane pilot is
constantly confronted with floating objects, some of which
are almost submerged and difficult to see - swimmers, skiers,
and a variety of watercraft. Before beginning the takeoff,
it is advisable to taxi along the intended takeoff path to
check for the presence of any hazardous objects or
obstructions. Thorough scrutiny should be given to the
area to assure not only that it is clear, but that it will
remain clear throughout the takeoff.
Operators of motorboats
and sailboats often do not realize the hazard resulting
from moving their vessels into the takeoff path of a
To accelerate during takeoff in a landplane, propeller
thrust must overcome only the surface friction of the
wheels and the increasing aerodynamic drag. During a
seaplane take-off, however, hydrodynamic or water drag
becomes 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
The hydrodynamic forces at work during a seaplane
takeoff run are shown in Figure 8. The point of greatest
resistance is referred to as the "hump" because the increasing
and decreasing effect of water drag causes a hump in
the resisting curve. After the hump is passed and the seaplane
is travelling on the step, water resistance decreases.
Figure 8: Water drag on take-off
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 this reason the
pilot should also practice takeoffs using only partial power
to simulate the long takeoff run usually needed when operating
at water areas where the density altitude is high and/
or the seaplane is heavily loaded.
The seaplane takeoff may be divided into four distinct
(1) The "displacement" phase,
(2) the "hump" or
(3) the "planing" or "on the step" phase,
and (4) the "lift off."
The first three phases were previously
described in the section on taxiing. The "lift off" is
merely transferring support of the seaplane from the floats
or hull to the wings by applying back elevator pressure.
This results in the seaplane lifting off the water and
becoming airborne. To avoid porpoising during the takeoff
run, it is important to maintain the proper pitch angles.
Too much back elevator pressure during the planing or lift
off phases will force the stern of the floats or hull deeper
into the water, creating a strong resistance and appreciably
retarding the takeoff. Conversely, insufficient back elevator
pressure will cause the bows to remain in the water,
which also results in excessive water drag. Experience will
determine the best angle to maintain during takeoff for
each seaplane, and if held at this angle, the seaplane will
take off smoothly.
Because the seaplane is not supported on a solid surface
and the float or one side of the hull can be forced
deeper into the water, right aileron control is usually
required to offset the effect of torque when full power is
applied during takeoff.
The spray pattern for each particular seaplane should
also be considered during takeoff. During acceleration the
water is increasingly sprayed upward, outward, and rearward
from the bow portion of the floats or hull, and on
some seaplanes will be directed into the propeller, eventually
causing erosion of the blades.
This water spray is
greater during the hump phase. The spray can be reduced
during takeoff, however, by first increasing the planing
speed about 10 knots, then opening the throttle as rapidly
as practical. This method shortens the time that propellers
are exposed to the spray. Again, the best technique must
be learned through experience with each particular seaplane.
Bear in mind that a rough water condition creates
more spray than does smooth water.
Glassy water takeoffs in a low-powered seaplane
loaded to its maximum authorized weight presents a difficult,
but not necessarily a dangerous, problem.
these conditions the seaplane may assume a "ploughing" or
nose-up position, but may not "unstick" or get "on the
step" because of the adhesive action of smooth water; consequently,
always plan ahead and consider the possibility
of aborting the takeoff. Nonetheless, if these conditions
are not too excessive, the takeoff can be accomplished
using the following procedure.
After the bow has risen to the highest point in the
ploughing position with full back elevator pressure, it should
be lowered by decreasing back elevator pressure. The bow
will drop if the seaplane has attained enough speed to be
on the verge of attaining the step position.
After a few seconds,
the bow will rise again. At the instant it starts to rise,
the rebound should be caught by again applying firm back
elevator pressure, and as soon as the bow reaches its maximum
height, the entire routine should be repeated. After
several repetitions, it will be noted that the bow attains
greater height and that the speed in increasing. If the elevator
control is then pushed well forward and held there,
the seaplane will slowly flatten out "on the step" and the
controls may then be eased back to the neutral position.
Whenever the water is glassy smooth, a takeoff can be
made with less difficulty by making the takeoff run across
the wakes created by motorboats. If boats are not operating
in the area, it is possible to create wakes by taxiing the
seaplane in a circle and then taking off across these self-made
On seaplanes with twin floats water drag can be
reduced by applying sufficient aileron pressure to raise the
wing and lift one float out of the water after the seaplane is
on the step. By allowing the seaplane to turn slightly in the
direction the aileron is being held rather than holding
opposite rudder to maintain a straight course, considerable
aerodynamic drag is eliminated, aiding acceleration and
lift off. When using this technique, great care must be
exercised so as not to lift the wing to the extent that the
opposite wing strikes the water. Naturally, this would
result in serious consequences.
In most cases an experienced seaplane pilot can safely
take off in rough water, but a beginner should not attempt
to takeoff if the waves are too high. Using the proper procedure
during rough water operation lessens the abuse of
the floats, as well as the entire seaplane.
During rough water takeoffs, the throttle should be
opened to takeoff power just as the bow is rising on a
wave. This prevents the bow from digging into the water
and helps keep the spray from the propeller. Slightly more
back elevator pressure should be applied to the elevator
than on a smooth water takeoff. This raises the bow to a
After planing has begun, the seaplane will bounce
from one wave crest to the next, raising the nose higher
with each bounce, and each successive wave will be struck
with increasing severity. To correct this situation and to
prevent a stall, smooth elevator pressures should be used
to set up a fairly constant pitch attitude that will allow the
aircraft to "skim" across each successive wave as speed
increases. Remember, in waves, the length of the float is
very important. It is important that control pressure be
maintained to prevent the bow from being pushed under
the water surface or "stubbing its toes," which could result
in capsizing the seaplane. Fortunately, a takeoff in rough
water is accomplished within a short time because if there
is sufficient wind to make water rough, the wind would
also be strong enough to produce aerodynamic lift earlier
and enable the seaplane to become airborne quickly.
With respect to water roughness, one condition that
seaplane pilots should be aware of is the effect of a strong
water current flowing against the wind.
For example, if the
velocity of the current is moving at 10 knots, and the wind
is blowing at 15 knots, the relative velocity between the
water and the wind is 25 knots. In other words, the waves
will be as high as those produced in still water by a wind
of 25 knots.
The advisability of cancelling a proposed flight because
of rough water depends upon the size of the seaplane,
wing loading, power loading, and, most important, the
pilot's ability. As a general rule, if the height of the waves
from trough to crest is more than 20 percent of the length
of the floats, takeoffs should not be attempted except by
the most experienced and expert seaplane pilots.
Downwind takeoffs are possible, and at times preferable,
if the wind velocity is light and normal takeoffs would
involve clearing hazardous obstructions, or flying over
congested areas before adequate altitude can be attained.
The technique used for downwind takeoffs is almost identical
to that used for upwind takeoffs.
The only difference
is that the elevator control should be held further aft, if
possible. When downwind takeoffs are made, it should be
kept in mind that more space is needed for the takeoff. If
operating from a small body of water, an acceptable technique
may be to begin the takeoff run while headed downwind,
and then turning so as to complete the takeoff into
the wind. This may be done by planing the seaplane while on a downwind
heading then making a step turn into the wind to complete the takeoff.
Caution must be exercised when using this technique sin