incorporate the movement of the water along with the
wind. The current may be a help or a hindrance, or
change from a help to a hindrance when the pilot
attempts to change direction. The keel effect only
works when the floats are moving through the water. If
the current is moving the seaplane, there may be little
or no motion relative to the water, even though the
seaplane is moving relative to the shore. Using wind,
current, and thrust to track the desired course requires
careful planning and a thorough understanding of the
various forces at work.
With the engine shut down, most flying boats sail
backward and toward whichever side the nose is
pointed, regardless of wind velocity, because the hull
does not provide as much keel effect as floats in pro-
portion to the side area of the seaplane above the
waterline. To sail directly backward in a flying boat,
release the controls and let the wind steer. Sailing is
an essential part of seaplane operation. Since each
type of seaplane has its own peculiarities, practice
sailing until thoroughly familiar with that particular
type. Practice in large bodies of water such as lakes
or bays, but sufficiently close to a prominent object in
order to evaluate performance.
Before taxiing into a confined area, carefully evaluate
the effects of the wind and current, otherwise the sea-
plane may be driven into obstructions. With a seaplane
of average size and power at idle, a water current of 5
knots can offset a wind velocity of 25 knots in the
opposite direction. This means that a 5 knot current
will carry the seaplane against a 25 knot wind.
Differential power can be used to aid steering in multi-
engine seaplanes.
PORPOISING
Porpoising is a rhythmic pitching motion caused by
dynamic instability in forces along the float bottoms
while on the step. An incorrect planing attitude sets off
a cyclic oscillation that steadily increases in amplitude
unless the proper pitch attitude is reestablished. [Figure
4-13]
A seaplane travels smoothly across the water on the
step only if the floats or hull remain within a moder-
ately tolerant range of pitch angles. If the nose is held
too low during planing, water pressure in the form of a
small crest or wall builds up under the bows of the
floats. Eventually, the crest becomes large enough that
the fronts of the floats ride up over the crest, pitching
the bows upward. As the step passes over the crest, the
floats tip forward abruptly, digging the bows a little
deeper into the water. This builds a new crest in front
of the floats, resulting in another oscillation. Each
oscillation becomes increasingly severe, and if not cor-
rected, will cause the seaplane to nose into the water,
resulting in extensive damage or possible capsizing. A
second type of porpoising can occur if the nose is held
too high while on the step. Porpoising can also cause a
premature lift-off with an extremely high angle of
attack, which can result in a stall and a subsequent
nose-down drop into the water. Porpoising occurs dur-
ing the takeoff run if the planing angle is not properly
controlled with elevator pressure just after passing
through the “hump” speed. The pitching created when
the seaplane encounters a swell system while on the
step can also initiate porpoising. Usually, porpoising
does not start until the seaplane has passed a degree or
two beyond the acceptable planing angle range, and
Right
Aileron Up
Left Rudder
Left Aileron
Down
Direction of Motion
with Engine Idling
Direction of Motion
with Power Just
Balancing Wind
Direction of Motion
with Enough Power
to Overcome Wind
Direction of Motion
with Power Off
Figure 4-12. By balancing wind force and engine thrust, it is
possible to sail sideways or diagonally forward. Of course,
reversing the control positions from those illustrated per-
mits the pilot to sail to the opposite side.
Figure 4-13. Porpoising increases in amplitude if not corrected promptly.
Ch 04.qxd 8/24/04 10:49 AM Page 4-9
does not cease until after the seaplane has passed out of
the critical range by a degree or two.
If porpoising occurs due to a nose-low planing attitude,
stop it by applying timely back pressure on the elevator
control to prevent the bows of the floats from digging
into the water. The back pressure must be applied and
maintained until porpoising stops. If porpoising does not
stop by the time the second oscillation occurs, reduce the
power to idle and hold the elevator control back firmly
so the seaplane settles onto the water with no further
instability. Never try to “chase” the oscillations, as this
usually makes them worse and results in an accident.
Pilots must learn and practice the correct pitch attitudes
for takeoff, planing, and landing for each type of sea-
plane until there is no doubt as to the proper angles for
the various maneuvers. The upper and lower limits of
these pitch angles are established by the design of the
seaplane; however, changing the seaplane’s gross
weight, wing flap position, or center of gravity location
also changes these limits. Increased weight increases
the displacement of the floats or hull and raises the
lower limit considerably. Extending the wing flaps fre-
quently trims the seaplane to the lower limit at lower
speeds, and may lower the upper limit at high speeds. A
forward center of gravity increases the possibility of
high angle porpoising, especially during landing.
SKIPPING
Skipping is a form of instability that may occur when
landing at excessive speed with the nose at too high a
pitch angle. This nose-up attitude places the seaplane at
the upper trim limit of stability and causes the seaplane
to enter a cyclic oscillation when touching the water,
which results in the seaplane skipping across the sur-
face. This action is similar to skipping flat stones across
the water. Skipping can also occur by crossing a boat
wake while taxiing on the step or during a takeoff.
Sometimes the new seaplane pilot confuses a skip with
a porpoise, but the pilot’s body sensations can quickly
distinguish between the two. A skip gives the body ver-
tical “G” forces, similar to bouncing a landplane.
Porpoising is a rocking chair type forward and aft
motion feeling.
To correct for skipping, first increase back pressure on the
elevator control and add sufficient power to prevent the
floats from contacting the water. Then establish the proper
pitch attitude and reduce the power gradually to allow the
seaplane to settle gently onto the water. Skipping
oscillations do not tend to increase in amplitude, as in
porpoising, but they do subject the floats and airframe
to unnecessary pounding and can lead to porpoising.
TAKEOFFS
A seaplane takeoff may be divided into four distinct
phases: (1) The displacement phase, (2) the hump or
plowing phase, (3) the planing or on the step phase, and
(4) the lift-off.
The displacement phase should be familiar from the
taxiing discussion. During idle taxi, the displacement
of water supports nearly all of the seaplane’s weight.
The weight of the seaplane forces the floats down into
the water until a volume that weighs exactly as much
as the seaplane has been displaced. The surface area of
the float below the waterline is called the wetted area,
and it varies depending on the seaplane’s weight. An
empty seaplane has less wetted area than when it is
fully loaded. Wetted area is a major factor in the cre-
ation of drag as the seaplane moves through the water.
As power is applied, the floats move faster through the
water. The water resists this motion, creating drag. The
forward portion of the float is shaped to transform the
horizontal movement through the water into an upward
lifting force by diverting the water downward.
Newton’s Third Law of Motion states that for every
action, there is an equal and opposite reaction, and in
this case, pushing water downward results in an
upward force known as hydrodynamic lift.
In the plowing phase, hydrodynamic lift begins push-
ing up the front of the floats, raising the seaplane’s nose
and moving the center of buoyancy aft. This, combined
with the downward pressure on the tail generated by
holding the elevator control all the way back, forces
the rear part of the floats deeper into the water. This
creates more wetted area and consequently more drag,
and explains why the seaplane accelerates so slowly
during this part of the takeoff.
This resistance typically reaches its peak just before
the floats are placed into a planing attitude. Figure 4-14
shows a graph of the drag forces at work during a sea-
plane takeoff run. The area of greatest resistance is
referred to as the hump because of the shape of the
water drag curve. During the plowing phase, the
increasing water speed generates more and more
hydrodynamic lift. With more of the weight supported
by hydrodynamic lift, proportionately less is supported
by displacement and the floats are able to rise in the
water. As they do, there is less wetted area to cause
drag, which allows more acceleration, which in turn
increases hydrodynamic lift. There is a limit to how far
this cycle can go, however, because as speed builds, so
does the amount of drag on the remaining wetted area.
Drag increases as the square of speed, and eventually
drag forces would balance the power output of the
engine and the seaplane would continue along the sur-
face without further acceleration.
Seaplanes have been built with sufficient power to
accelerate to takeoff speed this way, but fortunately the
step was invented, and it makes further acceleration
possible without additional power. After passing over
the hump, the seaplane is traveling fast enough that its
weight can be supported entirely by hydrodynamic lift.
Relaxing the back pressure on the elevator control
allows the float to rock up onto the step, and lifts the
Ch 04.qxd 8/24/04 10:49 AM Page 4-10
rear portions of the floats clear of the water. This elim-
inates all of the wetted area aft of the step, along with
the associated drag.
As further acceleration takes place, the flight controls
become more responsive, just as in a landplane.
Elevator deflection is gradually reduced to hold the
required planing attitude. As the seaplane continues to
accelerate, more and more weight is being supported
by the aerodynamic lift of the wings and water
resistance continues to decrease. When all of the
weight is transferred to the wings, the seaplane
becomes airborne.
Several factors greatly increase the water drag or
resistance, such as heavy loading of the seaplane or
glassy water conditions. In extreme cases, the drag may
exceed the available thrust and prevent the seaplane
from becoming airborne. This is particularly true when
operating in areas with high density altitudes (high ele-
vations/high temperatures) where the engine cannot
develop full rated power. For this reason the pilot should
practice takeoffs using only partial power to simulate
the longer takeoff runs needed when operating where
the density altitude is high and/or the seaplane is heavily
loaded. This practice should be conducted under the
supervision of an experienced seaplane instructor, and in
accordance with any cautions or limitations in the
AFM/POH. Plan for the additional takeoff area required,
as well as the flatter angle of climb after takeoff, and
allow plenty of room for error.
Use all of the available cues to verify the wind direc-
tion. Besides reading the water, pick up clues to the
wind’s direction from wind indicators and streamers
on the masts of moored boats, flags on flagpoles, or
rising smoke. A boat moored to a buoy points into the
wind, but be aware that it may have a stern anchor as
well, preventing it from pointing into the wind.
Waterfowl almost always align themselves facing into
the wind.
Naturally, be sure you have enough room for takeoff.
The landing distance of a seaplane is much shorter than
that required for takeoff, and many pilots have landed
in areas that have turned out to be too short for takeoff.
If you suspect that the available distance may be inad-
equate, consider reducing weight by leaving some of
your load behind or wait for more favorable weather
conditions. A takeoff that would be dangerous on a hot,
still afternoon might be accomplished safely on the fol-
lowing morning, with cooler temperatures and a brisk
wind.
In addition to wind, consider the effects of the current
when choosing the direction for takeoff. Keep in mind
that when taxiing in the same direction as the current,
directional control may be reduced because the seaplane
is not moving as quickly through the water. In rivers or
tidal flows, make crosswind or calm wind takeoffs in the
same direction as the current. This reduces the water
forces on the floats. Suppose the seaplane lifts off at 50
knots and the current is 3 knots. If winds are calm, the
seaplane needs a water speed of 47 knots to take off
downstream, but must accelerate to a water speed of 53
knots to become airborne against the current. This dif-
ference of 6 knots requires a longer time on the water
and generates more stress on the floats. The situation
becomes more complex when wind is a factor. If the
wind is blowing against the current, its speed can help
the wings develop lift sooner, but will raise higher
waves on the surface. If the wind is in the same direction
as the current, at what point does the speed of the wind
make it more worthwhile to take off against the current?
In the previous example, a wind velocity of 3 knots
would exactly cancel the benefit of the current, since the
air and water would be moving at the same speed. In
most situations, take off into the wind if the speed of the
wind is greater than the current.
Unlike landplane operations at airports, many other
activities are permitted in waters where seaplane
operations are conducted. Seaplane pilots encounter a
variety of objects on the water, some of which are
nearly submerged and difficult to see. These include
items that are stationary, such as pilings and buoys,
and those that are mobile, like logs, swimmers, water
skiers, and a variety of watercraft. Before beginning
the takeoff, it is a good practice to taxi along the
intended takeoff path to check for any hazardous
objects or obstructions.
Make absolutely sure the takeoff path ahead is free
of boats, swimmers, and other water traffic, and be
sure it will remain so for the duration of the takeoff
run. Powerboats, wind-surfers, and jet-skis can
move quickly and change direction abruptly. As the
POUNDS THRUST OR DRAG
KNOTS 20 40 60 80
"Hump"
Water
Drag
Propeller
Thrust
Figure 4-14. This graph shows water drag and propeller
thrust during a takeoff run.
Ch 04.qxd 8/24/04 10:49 AM Page 4-11
seaplane’s nose comes up with the application of full
power, the view ahead may be completely blocked by
the cowling. Check to the sides and behind the sea-
plane as well as straight ahead, since many watercraft
move much faster than the normal taxi speed and may
be passing the seaplane from behind. In addition to the
vessels themselves, also scan for their wakes and try to
anticipate where the wakes will be during takeoff.
Operators of motorboats and other watercraft often do
not realize the hazard caused by moving their vessels
across the takeoff path of a seaplane. It is usually better
to delay takeoff and wait for the swells to pass rather
than encountering them at high speed. Even small
swells can cause dangerous pitching or rolling for a
seaplane, so taxi across them at an angle rather than
head-on. Remember to check for other air traffic and
make any appropriate radio calls.
Be sure to use the pre-takeoff checklist on every take-
off. All checks are performed as the seaplane taxies,
including the engine runup. Hold the elevator control
all the way back throughout the runup to minimize
spray around the propeller. If there is significant wind,
let the seaplane turn into the wind for the runup. As
r.p.m. increases, the nose rises into the plowing posi-
tion and the seaplane begins to accelerate. Since this is
a relatively unstable position, performing the runup
into the wind minimizes the possibility of crosswinds,
rough water, or gusts upsetting the seaplane. Waste no
time during the runup checks, but be thorough and pre-
cise. Taxi speed will drop as soon as the power is
reduced.
Water rudders are normally retracted before applying
takeoff power. The buffeting and dynamic water pres-
sure during a takeoff can cause serious damage if the
water rudders are left down.
As full power is applied during takeoff in most sea-
planes, torque and P-factor tend to force the left float
down into the water. Right rudder pressure helps to
maintain a straight takeoff path. In some cases, left
aileron may also help to counter the tendency to turn
left at low speeds, by increasing drag on the right side
of the seaplane.
Density altitude is particularly important in seaplane
flying. High, hot, and humid conditions reduce engine
power and propeller efficiency, and the seaplane must
also attain a higher water speed in order to generate the
lift required for takeoff. This increase in water speed
means overcoming additional water drag. All of these
factors combine to increase takeoff distances and
decrease climb performance. In high density altitude
conditions, consider not only the length of the water
run, but the room required for a safe climbout as well.
The land area around a body of water is invariably
somewhat higher than the water surface. Tall trees are
common along shorelines, and in many areas, steep or
mountainous terrain rises from the water’s edge. Be
certain the departure path allows sufficient room for
safe terrain clearance or for a wide climbing turn back
over the water.
There are specific takeoff techniques for different
wind and water situations. Large water areas almost
always allow a takeoff into the wind, but there are
occasionally circumstances where a crosswind or
downwind takeoff may be more appropriate. Over the
years, techniques have evolved for handling rough
water or a glassy smooth surface. Knowing and prac-
ticing these techniques not only keep skills polished so
they are available when needed, they also increase
overall proficiency and add to the enjoyment of
seaplane flying.
NORMAL TAKEOFFS
Make normal takeoffs into the wind. Once the wind
direction is determined and the takeoff path chosen,
configure the seaplane and perform all of the pre-take-
off checks while taxiing to the takeoff position. Verify
that the takeoff will not interfere with other traffic,
either on the water’s surface or in the air.
Hold the elevator control all the way back and apply full
power smoothly and quickly, maintaining directional
control with the rudder. When the nose reaches its highest
point, ease the back pressure to allow the seaplane to
come up on the step. Establish the optimum planing atti-
tude and allow the seaplane to accelerate to lift-off speed.
In most cases, the seaplane lifts off as it reaches flying
speed. Occasionally it may be necessary to gently help
the floats unstick by either using some aileron to lift one
float out of the water or by adding a small amount of back
pressure on the elevator control. Once off the water, the
seaplane accelerates more quickly. When a safe airspeed
is achieved, establish the pitch attitude for the best rate of
climb (VY) and complete the climb checklist. Turn as
necessary to avoid overflying noise-sensitive areas, and
reduce power as appropriate to minimize noise.
CROSSWIND TAKEOFFS
In restricted or limited areas such as canals or narrow
rivers, it is not always possible to take off or land
directly into the wind. Therefore, acquiring skill in
crosswind techniques enhances the safety of seaplane
operation. Crosswinds present special difficulties for
seaplane pilots. The same force that acts to lift the
upwind wing also increases weight on the downwind
float, forcing it deeper into the water and increasing
drag on that side. Keep in mind that the allowable
crosswind component for a floatplane may be signifi-
cantly less than for the equivalent landplane.
Ch 04.qxd 8/24/04 10:49 AM Page 4-12
A crosswind has the same effect on a seaplane during
takeoff as on a landplane, that is, it tends to push the
seaplane sideways across the takeoff path, which
imposes side loads on the landing gear. In addition,
wind pressure on the vertical tail causes the seaplane to
try to weathervane into the wind.
At the beginning of the takeoff roll in a landplane, drift
and weathervaning tendencies are resisted by the fric-
tion of the tires against the runway, usually assisted by
nosewheel steering, or in some cases even differential
braking. The objective in a crosswind takeoff is the
same in landplanes and seaplanes: to counteract drift
and minimize the side loads on the landing gear.
The sideways drifting force, acting through the sea-
plane’s center of gravity, is opposed by the resistance of
the water against the side area of the floats. This creates
a force that tends to tip the seaplane sideways, pushing
the downwind float deeper into the water and lifting the
upwind wing. The partly submerged float has even more
resistance to sideways motion, and the upwind wing dis-
plays more vertical surface area to the wind, intensifying
the problem. Without intervention by the pilot, this tip-
ping could continue until the seaplane capsizes.
During a takeoff in stiff crosswinds, weathervaning
forces can cause an uncontrolled turn to begin. As the
turn develops, the addition of centrifugal force acting
outward from the turn aggravates the problem. The keels
of the floats resist the sideways force, and the upwind
wing tends to lift. If strong enough, the combination of
the wind and centrifugal force may tip the seaplane to
the point where the downwind float submerges and
subsequently the wingtip may strike the water. This is
known as a waterloop, and the dynamics are similar to a
groundloop on land. Although some damage occurs
when the wingtip hits the ground during a groundloop,
the consequences of plunging a wingtip underwater in a
seaplane can be disastrous. In a fully developed water-
loop, the seaplane may be severely damaged or may
capsize. Despite these dire possibilities, crosswind take-
offs can be accomplished safely by exercising good
judgment and proper piloting technique.
Since there are no clear reference lines for directional
guidance, such as those on airport runways, it can be
difficult to quickly detect side drift on water. Waves
may make it appear that the water is moving sideways,
but remember that although the wind moves the waves,
the water remains nearly stationary. The waves are
simply an up-and-down motion of the water surface—
the water itself is not moving sideways. To maintain a
straight path through the water, pick a spot on the shore
as an aim point for the takeoff run. On the other hand,
some crosswind techniques involve describing a
curved path through the water. Experience will help
determine which technique is most appropriate for a
given situation.
CONTROLLED WEATHERVANING
In light winds, it is easy to counteract the weathervan-
ing tendency during the early part of the takeoff run by
creating an allowance for it from the beginning. Prior
to adding takeoff power, use the water rudders to set up
a heading somewhat downwind of the aim point. The
angle will depend on the speed of the wind—the higher
Begin Takeoff by
Aiming Downwind of
the Intended Takeoff Path
Airplane
Weathervanes to
Intended Path
During Takeoff Run
Intended Takeoff Pat
Figure 4-15. Anticipate weathervaning by leading the aim point, setting up a somewhat downwind heading prior to starting the
takeoff. Choose an aim point that does not move, such as a buoy or a point on the far shore.
Ch 04.qxd 8/24/04 10:49 AM Page 4-13
the wind, the greater the lead angle. Create just enough
of a lead angle so that when the water rudders are raised
and power is applied, the seaplane weathervanes to the
desired heading during the time it gains enough speed
to make the air rudder and ailerons effective. As the
seaplane transitions to the plowing attitude, the weath-
ervaning tendency decreases as the fronts of the floats
come out of the water, adding vertical surface area at
the front of the seaplane. Use full aileron into the wind
as the takeoff run begins, and maintain enough aileron
to keep the upwind wing from lifting as airspeed builds.
[Figure 4-15 on previous page]
USING WATER RUDDERS
Another technique for maintaining a straight takeoff
path involves leaving the water rudders down to assist
with steering. Using the water rudders provides added
directional control until the aerodynamic controls
become effective.
To use this technique, align the seaplane with the aim
point on the shore, hold full aileron into the wind, and
apply takeoff power. As the seaplane accelerates, use
enough aileron pressure to keep the upwind wing
down. The downwind float should lift free of the water
first. After lift-off, make a coordinated turn to establish
the proper crab angle for the climb, and retract the
water rudders.
This takeoff technique subjects the water rudders to
high dynamic water pressures and could cause damage.
Be sure to comply with the advice of the float manu-
facturer. [Figure 4-16]
DOWNWIND ARC
The other crosswind takeoff technique results in a
curved path across the water, starting somewhat into the
wind and turning gradually downwind during the takeoff
run. This reduces the actual crosswind component at the
beginning of the takeoff, when the seaplane is most sus-
ceptible to weathervaning. As the aerodynamic controls
become more effective, the pilot balances the side loads
imposed by the wind with the skidding force of an inten-
tional turn, as always, holding the upwind wing down
with the ailerons. [Figure 4-17]
The pilot plans a curved path and follows this arc to
produce sufficient centrifugal force so that the seaplane
tends to lean outward against the wind force. During
the run, the pilot can adjust the rate of turn by varying
rudder pressure, thereby increasing or decreasing the
centrifugal force to compensate for a changing wind
force. In practice, it is quite simple to plan sufficient
curvature of the takeoff path to cancel out strong
crosswinds, even on very narrow rivers. Note that the
tightest part of the downwind arc is when the seaplane
is traveling at slower speeds.
The last portion of a crosswind takeoff is somewhat
similar to a landplane. Use ailerons to lift the down-
wind wing, providing a sideways component of lift to
counter the effect of the crosswind. This means that the
downwind float lifts off first. Be careful not to drop the
upwind wing so far that it touches the water. When
using a straight takeoff path, keep the nose on the aim
point with opposite rudder and maintain the proper step
attitude until the other float lifts off. Unlike a land-
plane, there is usually no advantage in holding the sea-
plane on the water past normal lift-off speed, and doing
so may expose the floats to unnecessary pounding as
they splash through the waves. Once airborne, make a
coordinated turn to the crab angle that results in a
straight track toward the aim point, and pitch to obtain
the desired climb airspeed.
Again, experience plays an important part in successful
operation during crosswinds. It is essential that all sea-
plane pilots have thorough knowledge and skill in these
maneuvers.
DOWNWIND TAKEOFFS
Downwind takeoffs in a seaplane present a somewhat
different set of concerns. If the winds are light, the
water is smooth, and there is plenty of room, a down-
wind takeoff may be more convenient than a long
downwind taxi to a position that would allow a takeoff
into the wind. In any airplane, the wing needs to attain
a specific airspeed in order to fly, and that indicated
airspeed is the same regardless of wind direction.
Start Takeoff Run with Water
Rudders Down.
Retract Water Rudders
After Lift-Off.
Continue Takeoff Using
Appropriate Aerodynamic
Controls
Figure 4-16. Remember to retract the water rudders after
takeoff to avoid damage during the next landing.
Ch 04.qxd 8/24/04 10:49 AM Page 4-14
However, when taking off downwind, obtaining the
airspeed means accelerating to a proportionately higher
groundspeed. Naturally, the takeoff run is longer
because the wings must first be accelerated to the speed
of the wind, then accelerated to the correct airspeed to
generate the lift required for takeoff. So far, this is
identical to what occurs with a landplane during a
downwind takeoff. But in addition, a downwind takeoff
run in a seaplane is further lengthened by the factor of
float drag. The speed of the floats in the water corresponds
to the higher groundspeed required in a landplane, but the
drag of the floats increases as the square of their speed.
This increase in drag is much greater than the increase
in rolling resistance of tires and wheel bearings in a
landplane. A tailwind may lengthen the seaplane’s
takeoff distance much more dramatically than the same
tailwind in a landplane.
Nevertheless, there are situations in which a downwind
takeoff may be more favorable than taking off into the
wind. If there is a long lake with mountains at the
upwind end and a clear departure path at the other, a
downwind takeoff might be warranted. Likewise, noise
considerations and thoughtfulness might prompt a
downwind takeoff away from a populated shore area if
plenty of water area is available. In areas where the
current favors a downwind takeoff, the advantage
gained from the movement of the water can more than
compensate for the wind penalty. Keep in mind that
overcoming the current creates far more drag than
accelerating a few extra knots downwind with the cur-
rent. In all cases, safety requires a thorough knowledge
of the takeoff performance of the seaplane.
GLASSY WATER TAKEOFFS
Glassy water makes takeoff more difficult in two
ways. The smoothness of the surface has the effect of
increasing drag, making acceleration and lift-off
more difficult. This can feel as if there is suction
between the water and the floats. A little surface
roughness actually helps break the contact between
the floats and the water by introducing turbulence and
air bubbles between water and the float bottoms. The
intermittent contact between floats and water at the
moment of lift-off cuts drag and allows the seaplane
to accelerate while still obtaining some hydrody-
namic lift, but glassy water maintains a continuous
drag force. Once airborne, the lack of visual cues to
the seaplane’s height above the water can create a
potentially dangerous situation unless a positive rate
of climb is maintained.
The takeoff technique is identical to a normal takeoff
until the seaplane is on the step and nearly at flying
speed. At this point, the water drag may prevent the
seaplane from accelerating the last few knots to lift-off
speed. To reduce float drag and break the grip of the
water, the pilot applies enough aileron pressure to lift
one float just out of the water and allows the seaplane
to continue to accelerate on the step of the other float
until lift-off. 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, be
careful not to lift the wing so much that the opposite
wing contacts the water. Obviously, this would have
serious consequences. Once the seaplane lifts off,
establish a positive rate of climb to prevent inadver-
tently flying back into the water.
Another technique that aids glassy water takeoffs
entails roughening the surface a little. By taxiing
around in a circle, the wake of the seaplane spreads and
reflects from shorelines, creating a slightly rougher
surface that can provide some visual depth and help
the floats break free during takeoff.
Occasionally a pilot may have difficulty getting the
seaplane onto the step during a glassy water takeoff,
particularly if the seaplane is loaded to its maximum
authorized weight. The floats support additional
weight by displacing more water; they sink deeper into
the water when at rest. Naturally, this wets more sur-
face area, which equates to increased water drag when
the seaplane begins moving, compared to a lightly
loaded situation. Under these conditions the seaplane
may assume a plowing position when full power is
applied, but may not develop sufficient hydrodynamic
lift to get on the step due to the additional water drag.
The careful seaplane pilot always plans ahead and con-
siders the possibility of aborting the takeoff.
Centrifugal Force
Figure 4-17.The downwind arc balances wind force with cen-
trifugal force.
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Nonetheless, if these conditions are not too excessive,
the takeoff often can be accomplished using the
following technique.
After the nose rises to the highest point in the plowing
position with full back elevator pressure, decrease back
pressure somewhat. The nose will drop if the seaplane
has attained enough speed to be on the verge of attain-
ing the step position. After a few seconds, the nose will
rise again. At the instant it starts to rise, reinforce the
rise by again applying firm back pressure. As soon as
the nose reaches its maximum height, repeat the entire
routine. After several repetitions, the nose attains
greater height and speed increases. 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. Once on the
step, the remainder of the takeoff run follows the usual
glassy water procedure.
ROUGH WATER TAKEOFFS
The objective in a rough water takeoff is similar to that
of a rough or soft field takeoff in a landplane: to transfer
the weight of the airplane to the wings as soon as possi-
ble, get airborne at a minimum airspeed, accelerate in
ground effect to a safe climb speed, and climb out.
In most cases an experienced seaplane pilot can safely
take off in rough water, but a beginner should not
attempt to take off 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, open the throttle to take-
off power just as the floats begin rising on a wave. This
prevents the float bows from digging into the water and
helps keep the spray away from the propeller. Apply a
little more back elevator pressure than on a smooth
water takeoff. This raises the nose to a higher angle
and helps keep the float bows clear of the water.
Once on the step, the seaplane can begin to bounce
from one wave crest to the next, raising its nose higher
with each bounce, so each successive wave is 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 allows
the seaplane to skim across each successive wave as
speed increases. Maintain control pressure to prevent
the float bows from being pushed under the water sur-
face, and to keep the seaplane from being thrown into
the air at a high pitch angle and low airspeed.
Fortunately, a takeoff in rough water is generally
accomplished within a short time because if there is
sufficient wind to make water rough, the wind is also
strong enough to produce aerodynamic lift earlier and
enable the seaplane to become airborne quickly.
The relationship of the spacing of the waves to the
length of the floats is very important. If the wavelength
is less than half the length of the floats, the seaplane is
always supported by at least two waves at a time. If
the wavelength is longer than the floats, only one wave
at a time supports the seaplane. This creates dangerous
pitching motions, and takeoff should not be attempted
in this situation.
With respect to water roughness, consider the effect of
a strong water current flowing against the wind. If the
current is moving at 10 knots and the wind is blowing
the opposite direction at 15 knots, the relative velocity
between the water and the wind is 25 knots, and the
waves will be as high as those produced in still water
by a wind of 25 knots.
The advisability of canceling a proposed flight because
of rough water depends on the size of the seaplane, wing
loading, power loading, and, most importantly, the
pilot’s ability. As a general rule, if the height of the
waves from trough to crest is more than half the height
of the floats from keel to deck, takeoffs should not be
attempted except by expert seaplane pilots. Chapter 8,
Emergency Open Sea Operations, contains more
information on rough water operations.
CONFINED AREA TAKEOFFS
If operating from a small body of water, an acceptable
technique may be to begin the takeoff run while
headed downwind, and then turning to complete the
takeoff into the wind. This may be done by putting the
seaplane on the step while on a downwind heading,
then making a step turn into the wind to complete the
takeoff. Exercise caution when using this technique
since wind and centrifugal force are acting in the same
direction and could result in the seaplane tipping over.
The water area must be large enough to permit a wide
step turn, and winds should be light.
In some cases, the water area may be adequate but
surrounding high terrain creates a confined area. The
terrain may also block winds, resulting in a glassy
water situation as well. Such conditions may lead to
a danger ous situation, especially when combined with
a high density altitude. Even though landing was not
difficult, careful planning is necessary for the takeoff. If
the departure path leads over high terrain, consider cir-
cling back over the water after takeoff to gain altitude. If
air temperatures have increased since landing, make the
proper allowance for reduced takeoff performance due
to the change in density altitude. Think about spending
the night to take advantage of cooler temperatures the
next morning. Although the decision may be difficult,
consider leaving some cargo or passengers behind if
takeoff safety is in question. It is far better to make a
second trip to pick them up than to end your takeoff in
the trees along the shore.