20.1 Seaplane and Water Operations Knowledge

FAA-S-ACS-6C is the ACS for the airplane category — single-engine land and sea, multiengine land and sea — so it carries a full set of seaplane knowledge elements. This section covers Task I.I (water and seaplane base characteristics), Task II.E (seaplane taxiing and sailing), the water takeoff and landing tasks in Area IV, and Task XII.B (seaplane postflight).

Reading the water surface

PA.I.I.K1 lists what to evaluate before committing to a landing area: size and location; protected versus unprotected areas; surface wind; direction and strength of the water current; floating and partially submerged debris; sandbars, islands, and shoals; vessel traffic and wakes; direction and height of waves; and any other characteristic specific to the area.

Two of those deserve emphasis. Current matters because a landing that looks fine against the wind may be badly downstream over the ground, and because docking is done against the stronger of wind or current. Debris is the seaplane equivalent of an obstacle on the runway, and a deadhead log floating just below the surface is invisible from pattern altitude.

The three surface conditions and the three techniques

Porpoising and skipping — the two named seaplane malfunctions

PA.I.I.K3 asks for the causes of porpoising and skipping and the pilot action to prevent or correct them, and these are exactly the kind of named-phenomenon items the test likes.

• Porpoising is a rhythmic longitudinal oscillation on the step, caused by planing at too low (too nose-down) a pitch attitude so the bows dig in and the airplane rocks fore and aft with increasing amplitude. Correction: apply back pressure to raise the nose to the correct planing attitude. If the oscillation does not stop within two or three cycles, close the throttle and let the floats settle off the step.
• Skipping is a bouncing off the tops of waves, caused by touching down in rough water at too high a pitch attitude or too fast — the airplane rebounds rather than settling. Correction: add power and go around, or lower the nose to the correct planing attitude if remaining on the water.

The symmetry is worth memorizing: porpoising is nose too low, skipping is nose too high.

Taxiing, sailing, and the water rudders

Task II.E covers taxiing and sailing. There are four distinct surface modes:

1. Displacement taxi — idle power, floats deep in the water, nose slightly high, a large bow wave. The slow, controllable mode. Water rudders down.
2. Plowing taxi — a transitional, very nose-high, high-drag attitude between displacement and step. Useful briefly for visibility over the nose; not for sustained taxiing, because it produces spray and heavy loads.
3. Step taxi — up on the step and planing, fast and efficient. Water rudders UP, because they will be damaged and are ineffective at speed.
4. Sailing — engine at idle or shut down, using the wind on the airframe with flaps, doors, and water rudders as sails to back the airplane into a dock or beach. A seaplane always weathervanes into the wind, and sailing works with that tendency rather than against it.

Water rudder discipline (PA.I.G.K1k) is a favorite test item: retracted for takeoff, landing, and step taxi; extended for displacement taxi, docking, and sailing.

Floats, charts, restrictions, and marine rules

Float and hull construction (PA.I.I.K2) changes performance: floats add weight and a great deal of parasite drag, so the takeoff run is longer, cruise speed is lower, and useful load is reduced. Floats are divided into watertight compartments — and every one of them must be pumped out before flight, because trapped water is both weight and an unknown CG shift.

Charts and directories (PA.I.I.K4): seaplane bases carry their own symbol on sectional charts, and the Chart Supplement lists seaplane bases along with their restrictions. Operating restrictions (K5) are frequently not FAA rules at all — state and local governments, wildlife refuges, and national parks regulate the water surface, and a lake that is aeronautically perfect may be legally closed.

Right-of-way on the water — 14 CFR 91.115:

• General. Each person operating an aircraft on the water shall, so far as possible, keep clear of all vessels and avoid impeding their navigation.
• Crossing. The aircraft or vessel to the other's right has the right-of-way.
• Head-on. Each shall alter course to the right to keep well clear.
• Overtaking. The craft being overtaken has the right-of-way; the one overtaking alters course to keep well clear.

Marine navigation aids (K7) include buoys, beacons, lights, sound signals, and range markers; in U.S. waters the convention is "red, right, returning" when returning from seaward. Naval Vessel Protection Zones (K8) extend 500 yards around a U.S. naval vessel: operate at the minimum speed necessary for safe navigation within 500 yards, and do not come within 100 yards without authorization. No-wake zones (K9) mean displacement taxi only.

Postflight (Task XII.B) is mooring, docking, anchoring, and beaching or ramping. All four are approached slowly, into the wind or current where possible, with the engine shut down early enough that you arrive with no more energy than you can absorb by hand, and with the floats protected from rocks and pilings.