Amphibious vehicle glossary

Shorthand for wheel layout: the first number is the total number of wheels and the second is how many are driven. Many amphibious ATVs are 6x6 or 8x8, with every wheel driven so the vehicle can climb out of water and mud.

The American Boat and Yacht Council, a nonprofit that writes technical standards for building boats in the United States, covering items such as electrical systems, fuel systems and ventilation. The standards are voluntary, but many builders and certification programs use them.

The formal name for a hovercraft: a vehicle that rides on a cushion of air held under it by a flexible skirt, so it can cross water, mud, ice and flat land. In the US Marine Corps, ACV also stands for Amphibious Combat Vehicle, a different, wheeled machine.

Hovercraft →

A short name for any amphibious vehicle or aircraft, borrowed from the animals that live both on land and in water.

A vehicle that can travel on land and on water under its own power, without being carried or towed between the two. The term covers cars that float, boats that drive, military landing vehicles, amphibious ATVs and, in a broader sense, hovercraft and amphibious aircraft.

How amphibious vehicles work → · What is an amphibious vehicle? →

Short for amphibious tractor, the name US forces used for tracked landing vehicles such as the LVT. Amtracs paddle through the water with their tracks and then drive straight up the beach.

Landing Vehicle Tracked (LVT, amtrac) →

The width of a boat at its widest point. A wide beam adds stability on the water, but road rules limit how wide an amphibious vehicle can be.

The lowest part of the inside of a hull, where any water that gets aboard collects.

A pump that removes water from the bilge. Amphibious vehicles usually carry more than one, because wheel wells, axle and steering seals, hatches and spray can all let water in.

The front of a boat or amphibious vehicle. The opposite end is the stern.

The upward push that water gives a floating object. It equals the weight of the water the object pushes aside, a rule known as Archimedes' principle. A vehicle floats when it can push aside its own weight in water before the water reaches its openings.

Bubbles of water vapor that form on a spinning propeller or impeller when the pressure on its blades drops too low. Cavitation wastes thrust and can pit the metal. It is a different problem from ventilation, where a propeller draws in air from the surface.

The European conformity mark. Recreational boats sold in the European Union must meet the Recreational Craft Directive and carry the CE mark, which covers design, construction, stability and buoyancy.

The line or edge where the bottom of a hull meets its sides. Hard chines help a planing hull lift onto plane and grip the water in turns.

The angle of a V-shaped hull bottom, measured up from horizontal. A deeper V cuts through waves more softly, while a flatter bottom planes more easily and draws less water.

The weight of water a floating vessel pushes aside, which is equal to the vessel's own weight. Boat weights are often given as displacement.

A hull that moves through the water rather than rising on top of it. Its practical top speed is limited by its waterline length, which is why most early amphibious cars, including the Amphicar, were slow on the water.

Amphicar 770 →

How deep the hull sits below the waterline. A shallow draft lets an amphibious vehicle reach beaches and shallow shorelines that deeper boats cannot.

The nickname of the World War II DUKW amphibious truck, and by extension of the amphibious tour vehicles descended from it.

GMC DUKW "Duck" →

General Motors' factory code for its 1942 amphibious truck. In GMC's system D meant a 1942 design, U meant utility (amphibious), K meant front-wheel drive and W meant two driven rear axles.

GMC DUKW "Duck" →

A World War II system that let a tank swim. A folding canvas screen raised around the hull gave it buoyancy, and propellers driven by the engine pushed it through the water. Known as DD tanks.

Closed-cell foam built into a hull so it stays afloat even if flooded. US Coast Guard rules require built-in flotation in most monohull boats under 20 ft (6.1 m) long.

Federal Motor Vehicle Safety Standards, the US safety rules that road vehicles must meet. FMVSS 500 is the standard for low-speed vehicles.

What is an LSV? →

The height from the waterline up to the lowest point where water could come aboard. Low freeboard is a common weakness of amphibious cars, because a car body sits low in the water and small waves can reach the doors or openings.

Hull Identification Number, the 12-character serial number that identifies a boat. Boats built or imported for sale in the United States have carried one since 1972. An amphibious vehicle sold in the US normally has both a HIN for the water and a VIN for the road.

A vehicle that floats on a cushion of air trapped under a flexible skirt and is pushed along by fans or propellers. Because it barely touches the surface, it can travel over water, mud, sand and ice.

Hovercraft →

The watertight body of a boat. In an amphibious boat the hull is the main structure and the wheels are added to it; in an amphibious car a car body is sealed so it can act as a hull.

A wing-shaped foil under a hull. As speed builds, the foil lifts the hull out of the water, cutting drag.

The spinning bladed rotor inside a water jet or pump that moves the water.

A propulsion system that draws water in through an opening under the hull and forces it out at high speed through a nozzle at the stern. The driver steers by turning the nozzle. There is no exposed propeller, which suits shallow water and beach landings.

How amphibious vehicles work →

A speed of one nautical mile per hour, about 1.15 mph or 1.85 km/h. Boat and military amphibian speeds are often given in knots.

A boat built to carry troops or vehicles from a ship to a beach and drop them through a ramp. Unlike an amphibious vehicle, a landing craft does not drive inland itself.

Landing Vehicle Tracked (LVT, amtrac) →

Lighter, Amphibious, Resupply, Cargo: a family of US Army amphibious vehicles that carry cargo from ships offshore onto the beach and inland. The number that follows gives the capacity, such as LARC-V for 5 tons.

LARC-V →

A sloped surface running into the water, used to launch and recover boats. Many amphibious vehicles use public ramps to drive in and out of the water, though local rules on ramp use vary.

Launching without a trailer →

Low-speed vehicle. In the United States, a four-wheeled motor vehicle whose top speed is more than 20 mph and not more than 25 mph, built to meet FMVSS 500. States decide which roads LSVs may use.

LSV rules and state guides → · LSV rules and state guides →

Landing Vehicle Tracked, the US Navy and Marine Corps name for the World War II amtracs and their successors.

Landing Vehicle Tracked (LVT, amtrac) →

A swamp vehicle that floats on large pontoons or wide tracks so it can cross wetlands that would trap a normal machine. Many carry excavator arms for dredging and wetland work.

A program of the National Marine Manufacturers Association in which inspectors check a boat model against US Coast Guard regulations and ABYC standards. Certified boats carry an NMMA plaque.

A self-contained engine, gearbox and propeller unit mounted on the transom of a boat. It steers by pivoting and can be tilted up out of the water, which suits amphibious boats that need the propeller clear of the ground on land.

The point at which a hull at speed rises up and skims across the top of the water instead of pushing through it. Planing needs enough power for the weight and a hull shape that can generate lift. Most amphibious cars cannot plane; high-speed amphibians are built to.

How amphibious boats get on plane →

A hull designed to rise onto plane at speed, usually with a V or flat bottom, hard chines and a flat run toward the stern.

Gibbs Aquada →

A sealed float that gives buoyancy. Pontoons support pontoon boats, some amphibious excavators and many bridging vehicles.

Left and right on a boat, as seen when facing the bow. Port is left and starboard is right.

A rotating set of angled blades that pushes against the water. Amphibious cars such as the Amphicar used small propellers driven from the engine, and steered in the water with their front wheels.

The extra floating volume of a hull above the waterline. The more reserve buoyancy a vehicle has, the more weight or water it can take before it sinks.

A blade at the stern that turns to steer a boat. Some amphibious vehicles use a rudder in the water; others steer with an outboard, a jet nozzle or their front wheels.

A raised air intake that lets an engine breathe when the vehicle sits low in the water or fords deep streams. Common on military amphibians and off-road vehicles.

The back of a boat or amphibious vehicle.

Military term for an amphibious vehicle moving through water under its own power, as in swim speed or swimming a river.

A vehicle that runs on continuous belts of track rather than wheels. Tracks spread the weight over soft ground, and on many amphibians they also paddle the vehicle through the water.

Iguana Yachts →

The moment an amphibious vehicle drives into or out of the water. Entry angle, bottom firmness, waves and current all matter, and each vehicle has its own procedure for lowering or raising wheels and switching propulsion.

The flat back panel of a boat's hull, where an outboard motor is mounted.

The United States Coast Guard, which sets federal rules for recreational boats, including capacity labels, flotation, navigation lights, safety equipment and the HIN.

Vehicle Identification Number, the 17-character code that identifies a road vehicle. Road-legal amphibious vehicles in the US carry a VIN in addition to the HIN for the hull.

The line where the surface of the water meets the hull when the vehicle floats at rest.

Raising the wheels up into or alongside the hull once in the water, so they stop dragging. Retraction is what lets high-speed amphibians plane, and it lowers the risk of wheels catching on rocks or weed.

Gibbs Aquada → · Sealegs →