Water and Seaplane Characteristics, Seaplane Bases, Maritime Rules, and Aids to Marine Navigation (ASES, AMES)

Glassy water is dangerous because it removes depth perception: with no discernible surface features on the calm, mirror-like surface, the pilot cannot judge height above the water, so a normal visual flare is unreliable (FAA-H-8083-23 glossary). The technique is a glassy water landing — a stabilized, power-on descent at a fixed attitude and rate, flown until touchdown occurs, rather than a flare judged by eye.

Teaching problem: the student's eyes will insist they can see the surface. Brief on the ground that the procedure is flown by attitude and rate, not by sight picture, and set the descent rate before the surface disappears.

• Size and location of the water area
• Protected versus unprotected areas
• Surface wind
• Current — direction and strength
• Debris — floating and partially submerged
• Sandbars, islands, and shoals
• Vessel traffic and wakes
• Wave direction and height
• Whatever is specific to the local area (AI.II.L.K1)

Add the handbook's own warning about takeoff room: the landing distance of a seaplane is much shorter than the distance required for takeoff, and many pilots have landed in areas that turned out to be too short for takeoff. If the distance may be inadequate, reduce weight or wait for more favorable conditions — a takeoff that would be dangerous on a hot, still afternoon may be safe the next morning with cooler temperatures and a brisk wind (FAA-H-8083-23 ch. 4).

Taxiing in the same direction as the current reduces directional control, because the seaplane is not moving as quickly through the water — the keel effect only works when the floats are moving through the water (FAA-H-8083-23 ch. 4). For crosswind or calm-wind takeoffs in rivers or tidal flows, take off in the same direction as the current to reduce water forces on the floats.

The handbook's arithmetic: if the seaplane lifts off at 50 knots and the current is 3 knots, it needs a water speed of 47 knots downstream but 53 knots against the current — a 6-knot difference that means longer time on the water and more stress on the floats (FAA-H-8083-23 ch. 4).

Scale of the effect: for a seaplane of average size and power at idle, a 5-knot current can offset a 25-knot wind in the opposite direction (FAA-H-8083-23 ch. 4).

(1) Displacement, (2) hump or plowing, (3) planing or "on the step," and (4) lift-off (FAA-H-8083-23 ch. 4).

1. Displacement — weight is supported by buoyancy; the floats sink until they displace a volume of water weighing exactly as much as the seaplane. The submerged surface is the wetted area, and it is a major source of drag.
2. Plowing — hydrodynamic lift pushes the float bows up, moving the center of buoyancy aft; combined with full aft elevator this forces the rear of the floats deeper, creating more wetted area and more drag. This is why acceleration is so slow here. Resistance peaks just before the floats reach a planing attitude — the hump on the water drag curve.
3. Planing — past the hump, weight can be supported entirely by hydrodynamic lift. Relaxing back pressure rocks the float up onto the step, clearing the rear of the floats and eliminating all wetted area aft of the step, along with its drag.
4. Lift-off — when all weight has transferred to the wings.

The step is an abrupt break in the longitudinal lines of the float or hull that reduces water drag and allows the pilot to vary the pitch attitude (FAA-H-8083-23 glossary). Without it, drag increases as the square of speed until it balances engine output and the seaplane simply stops accelerating along the surface — the handbook notes seaplanes have been built with enough power to force a takeoff that way, but the step makes further acceleration possible without additional power (FAA-H-8083-23 ch. 4).

Other structural members worth teaching (FAA-H-8083-23 glossary):

• Keel — guides the seaplane through the water and supports its weight on land
• Chine — the seam joining the sides to the bottom
• Spray rails — on the forward chines, keep spray out of the propeller
• Sister keelsons — provide rigidity and directional stability on the water
• Skeg — aft of the step, helps prevent the seaplane from tipping back onto the rear of the float

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 (FAA-H-8083-23 ch. 4).

Mechanism, nose-low: water pressure builds a crest under the float bows; the floats ride up over it, pitching the bows up; as the step passes the crest the floats tip forward abruptly, digging the bows deeper and building a new crest. Each oscillation is more severe, and uncorrected it will nose the seaplane into the water, causing extensive damage or possible capsizing. A second type occurs with the nose held too high on the step, which can also cause a premature lift-off at extremely high angle of attack, a stall, and a nose-down drop into the water.

Correction (nose-low): apply timely back pressure on the elevator to prevent the bows from digging in, and hold it until porpoising stops. If it has not stopped by the second oscillation, reduce power to idle and hold the elevator control back firmly so the seaplane settles onto the water with no further instability. Never "chase" the oscillations — that usually makes them worse and results in an accident.

Skipping is successive sharp bounces along the water surface caused by excessive speed or an improper planing attitude on the step — typically landing at excessive speed with the nose at too high a pitch angle, placing the seaplane at the upper trim limit of stability. It can also occur crossing a boat wake while on the step or during a takeoff (FAA-H-8083-23 ch. 4).

Telling them apart by feel: a skip gives vertical "G" forces, similar to bouncing a landplane; porpoising is a rocking-chair forward-and-aft motion.

Correction: increase back pressure on the elevator and add sufficient power to prevent the floats from contacting the water; then establish the proper pitch attitude and reduce power gradually to let the seaplane settle gently. Skipping oscillations do not tend to increase in amplitude the way porpoising does, but they pound the floats and airframe unnecessarily — and can lead to porpoising (FAA-H-8083-23 ch. 4).

The upper and lower limits are established by the seaplane's design, but they move with gross weight, wing flap position, and center of gravity location (FAA-H-8083-23 ch. 4):

• Increased weight increases float displacement and raises the lower limit considerably
• Extending flaps frequently trims the seaplane to the lower limit at lower speeds, and may lower the upper limit at high speeds
• A forward CG increases the possibility of high-angle porpoising, especially during landing

Porpoising usually does not start until the seaplane has passed a degree or two beyond the acceptable planing range, and does not cease until it has passed back out of the critical range by a degree or two — which is why the handbook insists pilots learn and practice the correct pitch attitudes for each type until there is no doubt about the proper angles.

Similar to, but not identical to, the in-flight rules (FAA-H-8083-23 ch. 1 quoting 91.115):

• General — each person operating an aircraft on the water shall, insofar as possible, keep clear of all vessels and avoid impeding their navigation, and give way to any vessel or other aircraft given the right-of-way by this section
• Crossing — the aircraft or vessel to the other's right has the right-of-way
• Approaching head-on — each shall alter course to the right to keep well clear
• Overtaking — the one being overtaken has the right-of-way; the one overtaking shall alter course to keep well clear
• Special circumstances — when risk of collision exists, each shall proceed with careful regard to existing circumstances, including the limitations of the respective craft

Inshore of the boundary line dividing the high seas from inland waters, follow the statutory Inland Rules (Pilot Rules); outside that line, follow the International Rules of the Sea, and all seaplanes must carry a current copy of the rules when operating in international waters (FAA-H-8083-23 ch. 1).

These rules apply because, under USCG regulations, the definition of a vessel includes virtually anything capable of being used for transportation on water — including seaplanes on the water — so a seaplane on the surface must comply with USCG navigation rules applicable to vessels; adhering to 91.115 should ensure compliance.

Inland waters are divided from international waters by buoys in areas with frequent ocean traffic, inshore of a line approximately parallel with the general trend of the shore drawn through the outermost buoy (FAA-H-8083-23 ch. 1).

Rotating beacon: the familiar beacon identifies lighted seaplane landing areas at night and in reduced visibility, but the colors alternate white and yellow for water landing areas; a double white flash alternating with yellow identifies a military seaplane base (FAA-H-8083-23 ch. 1).

Aeronautical charts: seaplane landing areas use symbols similar to land airports with the addition of an anchor in the center; tick marks around the outside denote fuel and services available, and a double ring identifies military facilities (FAA-H-8083-23 ch. 1).

Operating restrictions at individual bases (AI.II.L.K5, S6) come from the Chart Supplement and local sources — check them for each base you or your student will use.

The U.S. system uses a simple arrangement of colors, shapes, numbers, and lights. Buoys are floating markers held in place by cables or chains; daybeacons serve a similar purpose in shallower water, usually a marker on a piling or pole driven into the bottom (FAA-H-8083-23 ch. 1).

• Can buoys are cylindrical; nun buoys are conical. The shape often has significance.
• Approaching from seaward, the left (port) side of the channel is marked with black or green can buoys, using odd numbers that increase toward the coast. They also mark obstructions to be kept to the vessel's left when proceeding from seaward.
• The right side of the channel — and obstructions to be kept to the vessel's right when headed toward shore — are marked with red nun buoys, using even numbers that increase from seaward. The mnemonic is "red, right, returning."
• Black and white vertically striped buoys mark the center of the channel or fairway, and may use letters starting at A from seaward.
• At night: only the more important buoys are lighted. Some unlighted buoys carry red, white, or green reflectors with the same significance as lights of the same colors. Black or green buoys have green or white lights; red buoys have red or white lights. Buoys with a red band at the top carry red lights.

Two cautions: the chain holding a buoy is likely several times the depth of the water, so the buoy may be some distance from its charted location and from the hazard it marks — do not come any closer to a buoy than necessary. And other buoyage systems exist in the U.S. and abroad, sometimes with exactly the opposite meanings, so learn the system used where you fly (FAA-H-8083-23 ch. 1).

Ranges are pairs of beacons that mark a safe course when the two structures appear in line — typically a channel centerline. They display rectangular daymarks of various colors and are generally, but not always, lighted (33 CFR 62.41). The caution to teach: a range does not tell you how far it is safe to follow — consult the chart to learn which section may be safely traversed, since a range held past its usable limit leads straight into shoal water.

Sound signals warn mariners of proximity to danger when visual signals are obscured, and sit on or beside an aid (33 CFR 62.47). Never navigate by them:

• Distance cannot be judged by sound intensity.
• There are places close to a signal where it cannot be heard, and fog near — but not at — the source can block it entirely.
• Buoy-mounted signals are actuated by sea motion, so they may not sound at all in calm conditions — exactly the glassy-water day when you most want them.
• A buoy is not on a fixed position, so the sound is not coming from a fixed position either.

Teaching angle: pair this with the buoy-chain caution. Every marine aid tells you roughly where something is, never exactly.

A seaplane on the water is a vessel under Coast Guard rules, so both apply to you.

Naval vessel protection zone — a 500-yard regulated area around any large U.S. naval vessel (a U.S. naval vessel over 100 feet in length), whether moored, anchored, or underway (33 CFR 165.2015). Inside 500 yards, operate at the minimum speed necessary to maintain a safe course. No vessel or person may come within 100 yards of a large naval vessel without authorization from the Coast Guard, the senior naval officer present, or the official patrol — request it on VHF-FM channel 16 (33 CFR 165.2025). This is an armed-enforcement zone, not an advisory one.

No wake zones — controlled areas established by state and local authority, marked by information and regulatory marks: white with two horizontal orange bands and an orange shape (33 CFR 62.33).

• Open circle — operating restrictions in effect inside the marked area (a speed or no-wake limit)
• Square or rectangle — lettered instructions
• Open diamond — danger
• Crossed diamond — vessels excluded entirely

Instructor point: your wake is your responsibility. Docks, moored boats, and swimmers are what those zones protect, and a step taxi through one is both a violation and how seaplane operations get banned from a lake.

Many seaplane landing areas are a stretch of water and nothing else — no fuel, no maintenance, no line service, no one to call, and possibly no cell coverage. The chart gives the first warning: FAA-H-8083-23 ch. 1 distinguishes a civil seaplane base from one annotated "No Facilities, or Complete Information is Not Available."

What that changes in the preflight, and what you must make the student build a habit of:

• Fuel is a closed loop. Plan to return with reserves; do not plan on buying fuel that may not exist, may be the wrong grade, or may be behind a locked gate.
• A mechanical problem is a recovery problem. Consider how the airplane gets out if it will not start — and remember the handbook's warning that landing distance is far shorter than takeoff distance, so a marginal area is a one-way trip.
• Docking and mooring may be improvised. Know the beaching, docking, and sailing techniques before you need them at a site with no dock.
• Carry survival equipment appropriate to the area, and know how to use it — FAA-H-8083-23 ch. 7 makes the point for remote operations directly.
• Tell someone. A flight plan or a named person expecting you at a time is the only search trigger at a base with no one on it.

Teach it as a go/no-go input rather than trivia: "what does this base actually provide?" belongs in the student's planning flow next to weather and takeoff distance.

The person pushing off or mooring a seaplane at a dock is allowed to move around while the seaplane is in motion on the surface — an exception to the normal rule requiring everyone to have a seat and wear a seatbelt during surface movement (FAA-H-8083-23 ch. 1, 91.107).

Related certification note: because seaplanes seldom have retractable landing gear as such, 61.31 accounts for this — an endorsement to act as PIC of a complex seaplane requires training in a seaplane with flaps and a controllable pitch propeller (FAA-H-8083-23 ch. 1).