Glossary.qxd 8/25/04 11:35 AM Page G-3 SKIDS-ON-FLOATS —A type of helicopter float design where the rigid portion of the landing gear rests on the floats. The floats sup- port the whole weight of the heli- copter in water or on hard surfaces. by underwater disturbances such as volcanoes or earthquakes. The waves have a uniform and orderly appearance characterized by smooth, rounded, regularly spaced wave crests. TIP FLOATS —Small floats near the wingtips of flying boats or floatplanes with a single main float. The tip floats help stabilize the air- plane on the water and prevent the wingtips from contacting the water. SKIPPING  — Successive sharp bounces along the water surface caused by excessive speed or an improper planing attitude when the seaplane is on the step. SPONSONS —Short, winglike pro- jections from the sides of the hull near the waterline of a flying boat. Their purpose is to stabilize the hull from rolling motion when the flying boat is on the water, and they may also provide some aerodynamic lift in flight. Tip floats also are sometimes known as sponsons. SWELL DIRECTION  — The direction from which a swell is moving. Once set in motion, swells tend to maintain their original direc- tion for as long as they continue in deep water regardless of wind direction. Swells may be moving into or across the local wind.  TROUGH —The low area between two wave crests. TRANSOM —As it applies to seaplanes, the rear bulkhead of a float. SWELL FA CE —The side of the swell toward the observer. The back is the side away from the observer. These terms apply regardless of the direction of swell movement. UPSWELL —Motion opposite the direction the swell is moving. If the swell is moving from north to south, a seaplane going from south to north is moving upswell. SPRAY RAILS —Metal flanges attached to the inboard forward por- tions of the chines to reduce the amount of water spray thrown into the propeller. SWELL LENGTH —The horizon- tal distance between successive crests. VESSEL —Anything capable of being used for transportation on water, including seaplanes. STARBOARD —The right side or the direction to the right of a vessel. STEP —An abrupt break in the longitudinal lines of the float or hull, which reduces water drag and allows the pilot to vary the pitch attitude when running along the water’s surface. STEP 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 planing posi- tion. SWELL PERIOD — The time interval between the passage of two successive crests at the same spot in the water measured in seconds. SWELL VELOCITY  — The velocity with which the swell advances with relation to a fixed reference point, measured in knots. There is little movement of water in the horizontal direction. Each water particle transmits energy to its neighbor resulting primarily in vertical motion, similar to the motion observed when shaking out a carpet. TIDES —The alternate rising and falling of the surface of the ocean and other bodies of water connected with the ocean.  They are caused by the gravitational attraction of the sun and moon occurring unequally on different parts of the earth. Tides typically rise and fall twice a day. SWELL —Waves that continue after the generating wind has ceased or changed direction. Swells also are generated by ships and boats in the form of wakes, and sometimes WING FLOATS —Stabilizer floats found near the wingtips of flying boats and single main float float- planes to prevent the wingtips from contacting the water. Also called tip floats. WINDWARD —Upwind, or the upwind side of an object. WEATHERVANING —The ten- dency of an aircraft to turn until it points into the wind. WATER RUDDERS — Retractable control surfaces on the back of each float that can be extended downward into the water to provide more directional control when taxiing on the surface. They are attached by cables and springs to the air rudder and operated by the rudder pedals in the cockpit. G-3