Design Pump-jet

1 design

1.1 axial flow
1.2 mixed flow
1.3 centrifugal flow

design

this image illustrates workings of reversing bucket. 1: forward thrust, reversing bucket disengaged 2: reverse thrust, reversing bucket pushes thrust flow backwards



forward, back, side & turn pump-jet

a pump-jet works having intake (usually @ bottom of hull) allows water pass underneath vessel engines. water enters pump through inlet. pump can of centrifugal design high speeds, or axial flow pump low medium speeds. water pressure inside inlet increased pump , forced backwards through nozzle. use of reversing bucket, reverse thrust can achieved faring backwards, , without need change gear or adjust engine thrust. reversing bucket can used slow ship down when braking. feature main reason pump jets maneuverable.

the nozzle provides steering of pump-jets. plates, similar rudders, can attached nozzle in order redirect water flow port , starboard. in way, similar principles of air thrust vectoring, technique has long been used in launch vehicles (rockets , missiles) later in military jet-powered aircraft. provides pumpjet-powered ships superior agility @ sea. advantage when faring backwards using reversing bucket, steering not inverted, opposed propeller-powered ships.

axial flow

an axial-flow waterjet s pressure increased diffusing flow passes through impeller blades , stator vanes. pump nozzle converts pressure energy velocity, producing thrust.

axial-flow waterjets produce high volumes @ lower velocity, making them suited larger low medium speed craft, exception being personal water craft, high water volumes create tremendous thrust , acceleration high top speeds. these craft have high power-to-weight ratios compared marine craft. axial-flow waterjets far common type of pump.

mixed flow

mixed-flow waterjet designs incorporate aspects of both axial flow , centrifugal flow concepts. pressure developed both diffusion , radial outflow.

mixed flow designs produce lower volumes of water @ high velocity making them suited small moderate craft sizes , higher speeds. common uses include high speed pleasure craft, , waterjets shallow water river racing (see river marathon).

centrifugal flow

centrifugal-flow waterjet designs make use of radial flow create water pressure.

centrifugal designs not commonly used anymore except on outboard sterndrives.