HYDRODYNAMIC FORCES Forces relating to the motion of fluids and the effects of fluids acting on solid bodies in motion relative to them.

HYDRODYNAMIC LIFT For seaplanes, the upward force generated by the motion of the hull or floats through the water. When the seaplane is at rest on the surface, there is no hydrodynamic lift, but as the seaplane moves faster, hydrodynamic lift begins to support more and more of the seaplane’s weight.

IDLING POSITION The attitude of the seaplane when its entire weight is supported by the buoyancy of the floats, as it is when at rest or during a slow taxi. Also called the displacement position.

KEEL A strong longitudinal member at the bottom of a float or hull that helps guide the seaplane through the water, and, in the case of floats, supports the weight of the seaplane on land.

LEEWARD Downwind, or the downwind side of an object.

MOOR To secure or tie the seaplane to a dock, buoy, or other stationary object on the surface.

NUN BUOYS Conical buoys marking the left side of a channel for an inbound vessel. They often have even numbers that increase as the vessel progresses from seaward.

PLAIN SKI A type of aircraft ski that can only be used on snow or ice, as compared to combination skis, which also allow the use of the skiplane’s wheels for landing on runways.

PLANING POSITION The attitude of the seaplane when the entire weight of the aircraft is supported by hydrodynamic and aerodynamic lift, as it is during high-speed taxi or just prior to takeoff. This position produces the least amount of water drag. Also called the step position, or “on the step.”

PLOWING POSITION A nose high, powered taxi characterized by high water drag and an aftward shift of the center of buoyancy. The weight of the seaplane is supported primarily by buoyancy, and partially by hydrodynamic lift.

POP-OUT FLOATS Helicopter floats that are stored deflated on the skids or in compartments along the lower portion of the helicopter, and deployed in the event of an emergency landing on water. Compressed nitrogen or helium inflates the floats very quickly.

PORPOISING A rhythmic pitching motion caused by an incorrect planing attitude during takeoff.

PORT The left side or the direction to the left of a vessel.

PRIMARY SWELL The swell system having the greatest height from trough to crest.