Rough Water Takeoff and Climb (ASES, AMES)

The objective in a rough water takeoff is similar to that of a rough or soft field takeoff in a landplane: transfer the weight of the airplane to the wings as soon as possible, get airborne at a minimum airspeed, accelerate in ground effect to a safe climb speed, and climb out (FAA-H-8083-23 ch. 4).

That analogy is the most useful teaching device in the Task, because a student who already flies soft-field takeoffs in a landplane has the motor pattern — you are transferring a known skill to a new surface. What is new is the timing (waves) and the failure mode (the float bows).

The secondary purpose: using the proper procedure during rough water operation lessens the abuse of the floats, as well as the entire seaplane.

• Lift off at minimum airspeed and accelerate to VY ±5 knots before leaving ground effect
• Maintain VY ±5 knots to a safe maneuvering altitude
• Configure after a positive rate of climb has been verified, or per the manufacturer
• Maintain directional control and proper wind-drift correction throughout takeoff and climb
• Verify the assigned/correct takeoff path, and determine wind direction with or without visible indicators
• Position flight controls and configure for the existing conditions
• Clear the area and select an appropriate takeoff path considering wind, swells, surface hazards, or vessels
• Retract the water rudders
• Establish and maintain an appropriate planing attitude and directional control, correcting for porpoising, skipping, and increased water drag
• Avoid excessive water spray on the propeller(s)
• Analyze and correct common errors (S15)

Open the throttle to takeoff power just as the floats begin rising on a wave (FAA-H-8083-23 ch. 4).

Two reasons: it prevents the float bows from digging into the water, and it helps keep spray away from the propeller.

Pitch rule: 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.

Narration: "Watching the swell… bows coming up — power now. Extra back pressure, keep those bows out of the next one."

It is a divergent condition, and left alone it ends in a stall or a nose-in: once on the step, each bounce raises the nose higher, so each successive wave is struck with increasing severity (FAA-H-8083-23 ch. 4).

Correction:

• Use smooth elevator pressures to set up a fairly constant pitch attitude, letting the seaplane skim across each successive wave as speed increases
• Maintain control pressure to prevent the float bows from being pushed under the water surface — bows under on the low side
• Avoid letting the seaplane be thrown into the air at a high pitch angle and low airspeed on the high side
• Never try to "chase" the oscillations — this usually makes them worse and results in an accident (FAA-H-8083-23 ch. 4); the coaching word is smooth

One consolation to give the student: 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.

Two rules, and both are stated as thresholds (FAA-H-8083-23 ch. 4):

• 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.
• Wavelength versus float length: 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 it — this creates dangerous pitching motions, and takeoff should not be attempted.

The judgment framing: 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. Teach the two measurements first so the judgment has something to stand on — and note that 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.

They add. Consider 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 water and wind is 25 knots, and the waves will be as high as those produced in still water by a wind of 25 knots (FAA-H-8083-23 ch. 4).

Teach the student to survey the water, not the windsock. A 15-knot wind report on a fast-flowing river is a 25-knot sea state, and the wave-height and wavelength rules are measured against what is actually there.

The corresponding planning fact for takeoff direction: 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 — because overcoming the current creates far more drag than accelerating a few extra knots downwind with the current.

Because float drag increases as the square of water speed. The speed of the floats in the water corresponds to the higher groundspeed required in a landplane, but float drag rises far more steeply with speed than the rolling resistance of tires and wheel bearings does. A tailwind may lengthen the seaplane's takeoff distance much more dramatically than the same tailwind in a landplane (FAA-H-8083-23 ch. 4).

There are still legitimate reasons to take off downwind — a long lake with mountains at the upwind end and a clear departure path at the other, noise considerations, or a favorable current — but on rough water the answer is usually no, because rough water is usually an indication of strong winds, and vice versa (FAA-H-8083-23 ch. 6), and a strong tailwind on rough water combines the worst of both.

Teaching test: make the student justify a downwind takeoff out loud, against the departure path and the water distance available.

Briefed before the run, using the handbook's own thresholds:

• The two wave rules — trough-to-crest more than half the float height, or wavelength longer than the floats: do not attempt (FAA-H-8083-23 ch. 4)
• A distance point for being on the step and a distance point for lift-off, measured against the water available and the departure path
• The porpoising trigger, and it is countable — if porpoising does not stop by the second oscillation, reduce power to idle and hold the elevator control back firmly so the seaplane settles with no further instability (FAA-H-8083-23 ch. 4). That is your "I have the flight controls" moment (AIH ch. 9)
• Engine failure — as in any takeoff, control first; a seaplane has the advantage that the surface below is landable, but a high-pitch, low-airspeed condition off a wave crest is a stall, not a glide
• Gear position in an amphibious airplane (AI.VII.K.R7) — confirmed verbally and visually before the run (FAA-H-8083-23 ch. 6)

And apply the AIH's limit rule as your own: learners should never be allowed to exceed the flight instructor's limits, and instructors should not exceed their own ability to perceive a problem, decide upon a course of action, and physically react (AIH ch. 9). Rough water compresses all three.

Weight the explanation phase — objectives, completion standards, the precise actions, the end result of those efforts, and safety procedures, with time for questions before you leave the ground (AIH ch. 9). In a simulated Task the brief carries most of the learning.

Then make the airborne portion faithful where it can be:

• Fly the soft-field analogue in the seaplane on calm water — early back pressure, lift off at minimum airspeed, accelerate to VY in ground effect before climbing — because that is the skeleton of the maneuver (AI.VII.K.S11)
• Practice the survey and the go/no-go arithmetic on real water using the two wave rules, even when the answer is obviously "go"
• Rehearse the porpoising correction verbally and, if conditions permit, in the benign form produced by crossing a boat wake — noting that a wake crossing on the step is a listed cause of skipping (FAA-H-8083-23 ch. 4)
• Use learner tells, instructor does — the student calls the power timing ("bows rising — power"), the extra back pressure, and the abort trigger while you fly (AIH ch. 9)

Debrief with collaborative assessment: learner self-assessment first, then your comparison (AIH ch. 9).

The definitions, at instructor depth (AFH ch. 6): VX is the speed at which the airplane achieves the greatest gain in altitude for a given distance over the ground; it is usually slightly less than VY, which is the greatest gain in altitude per unit of time. VX is where excess thrust peaks; VY is where excess power peaks.

Why VY is the graded number here: the rough water Task asks you to lift off at minimum airspeed and accelerate to VY ±5 knots before leaving ground effect, then maintain VY ±5 knots to a safe maneuvering altitude (AI.VII.K.S11, S13). The maneuver's whole purpose is to transfer the weight of the airplane to the wings as soon as possible, get airborne at a minimum airspeed, accelerate in ground effect to a safe climb speed, and climb out (FAA-H-8083-23 ch. 4) — the constraint is the water surface, not an obstacle, so you buy altitude per second and get away from the waves.

Where VX takes over: an obstacle or rising terrain in the departure path, which is Task VII.G's standard (VX ±5 knots until the obstacle is cleared or 50 feet AGL). Rough water and confined terrain frequently coexist, so brief which speed governs before the run.

The instructor-depth warning to attach: the airplane is lifted off at minimum airspeed, so it leaves the water below both speeds and accelerates in ground effect. Attempting to climb prematurely out of ground effect at that point is the maneuver's characteristic accident — and in some airplanes a deviation of 5 knots may result in a significant reduction in climb performance (AFH ch. 6).

The Seaplane Handbook prints no numbered common-error list, so build one from the failure modes it describes (FAA-H-8083-23 ch. 4). Name the error, then the corrective phrase:

• Attempting the takeoff at all when the two thresholds say no — waves more than half the float height from keel to deck, or wavelength longer than the floats, which creates dangerous pitching motions
• Reading the windsock instead of the water — a 15-knot wind opposing a 10-knot current is a 25-knot sea state
• Applying power at the wrong moment in the wave cycle — open the throttle to takeoff power just as the floats begin rising on a wave
• Not enough back pressure — apply a little more back elevator pressure than on a smooth water takeoff to keep the float bows clear
• Bows digging in, or the opposite, being thrown into the air at a high pitch angle and low airspeed — the two failure modes bracketing the correct attitude
• Chasing the bouncing with abrupt inputs instead of smooth elevator pressures to set up a fairly constant pitch attitude; never try to "chase" the oscillations
• No porpoising abort trigger — idle power and firm back elevator by the second oscillation
• Excessive water spray on the propeller(s) (S14) from a low nose in the plow
• Climbing out of ground effect before VY rather than accelerating to VY ±5 knots before leaving ground effect (S11)

The teaching order matters: the first two errors are made on the beach, before the engine starts, and they are the only ones on the list that a student cannot recover from with technique.