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  1. #1

    Purpose of the pump?

    Can someone please explain the purpose of the pump? I understand how the impeller works and that the force it create spins the pump (essentially a turbine)... but what would the SKI do without a pump?would it be faster? Slower?

    the impeller is moving the water, but why is the pump there?!

    Some detailed explaing of what the pump does and not how a PWC jet drive works would be great. There's plenty of information of how anpwc jet works but it doesn't detail the pump and it's role.

    thank you.

  2. #2
    Click avatar for tech links/info K447's Avatar
    Join Date
    Jul 2007
    near Toronto, Canada
    Why not just have a propeller hanging under the hull in the water, is that the question?

    The spinning impeller accelerates the water rearwards, obviously. It also imparts a rotational spin to the water. The curved stator vanes convert the water spin back into additional directional flow rearwards.

    The tapered jet pump exit nozzle narrows the water path, forcing the water to increase in velocity and pressure. This increases the effective thrust from the jet pump at speed. Within a range, a smaller exit nozzle will produce higher watercraft top speed but reduce initial acceleration.

    At speed, the enclosed intake under the hull ensures that the impeller receives a solid flow of water with no or minimal air mixed into the water. Water does not compress, air does. The jet pump requires solid water to produce the desired high thrust.

    The water jet also allows steering with the steering nozzle. Without the nozzle, steering would require a rudder. Reverse and neutral are possible using a bucket positioned behind the jet pump, unlike a boat that requires a gearbox to actually change the rotation direction of the propeller. PWC has no transmission, the impeller is always turning with the engine and always in the same direction.

    With the entire propulsion unit tucked up into the hull, the PWC can operate in shallower water than a traditional boat propeller, and accelerate much harder.

    Here is some info on an experimental propeller conversion watercraft.

  3. #3
    GGG's Avatar
    Join Date
    Sep 2009
    Jersey Shore
    i would say a major reason would be safety. for 2 reasons. there's no prop to chop you up and the the pump is more stable at high speed

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