WHY JET PROPULSION? - Jet propulsion is widely used today for many high speed vessels including large commercial passenger ferries, rescue craft, military patrol boats and offshore supply vessels. Yamaha saw the benefits, performance, efficiency, and safety of waterjets when they entered the Watercraft arena in 1986 with its popular Waverunner and 1999 with its Sport Jet Boats. Yamaha has become the leader in recreational jet watercraft, bringing its extensive single and twin small engine technologies to the water.
Jetboats were originally designed by Sir William Hamilton who developed a waterjet in 1954 for operation in the fast-flowing and shallow rivers of New Zealand, specifically to overcome the problem of propellers striking rocks in such waters. Jets at speed can typically operate in as little as 3 inches of water safely.
HiGHLY MANEUVERABLE - Jet boats are highly maneuverable, and many can, from full speed, be reversed and brought to a stop within little more than their own length, in a maneuver known as a "crash stop". The Navy Seals PBR Mark II (Pibber) was known to be able to turn around 180 degrees within its length from speed as a lifesaving manoever, and today the Navy Seals employ twin jet propulsion in their efficient Mark V.1 patrol craft. (The well known Hamilton turn or "jet spin" is a high speed maneuver where the boat's engine throttle is cut, the steering is turned sharply and the throttle opened again causing the boat to spin quickly around with a large spray of water.)
MORE EFFICIENCY PERFORMANCE - Traditional prop-drives are generally more efficient and economical at low speeds, but as boat speed increases beyond this, the extra hull resistance generated by struts, rudders, shafts etc results in jet propulsion, thrusting above the water, becoming more efficient in speeds over 20 knots (23 mph.) Thus, the vast majority of waterjet units are installed in high speed vessels, and, in particular, situations where shallow draft, maneuverability and load flexibility are primary concerns. A jet propulsion unit that is well matched to the engine is MORE fuel efficient that a propeller because it does not waste power by throwing water radially. Further, typically the engine in a jetboat is directly coupled to the pump shaft eliminating the need for a gearbox and therefore eliminating any gearbox losses. (Most propeller driven vessels have gearboxes in which measurable power is lost resulting in increased fuel consumption and reduced performance.) Generally, a jet boat will normally use about half the fuel that a boat of the same size does which is propelled by an outboard motor at the same speed. The main reason most commercial ferries use jets is to reduce fuel consumption.
GREATEST SAFETY - One very important feature of the jetboat is the fact that it has no external rotating parts; it is thus safer for swimmers and marine life, though these can still be struck by the hull. The safety benefit itself can sometimes be reason enough to use this type of propulsion.