HP(human-powered) jet drive?

Discussion in 'Jet Drives' started by bluekayak, Apr 27, 2012.

  1. bluekayak
    Joined: Mar 2006
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    Location: Menlo Park, California

    bluekayak Junior Member

    Hi -

    Am pondering kayak design and wondering if (small) jet drive would work on kayak, meaning powered by pedal

    Is that an utterly impractical idea? Thinking that maybe some of limitations/requirements would be less relevant in context of a very light-weight vessel that isn't being designed to break speed records

    Also wondering about questions e.g. what horsepower requirements are, and guessing jet drives require higher rpm etc

    Recently saw that some surfboards are using small jet drive of some sort, which is what got me going on this

    Thanks much
  2. Submarine Tom

    Submarine Tom Previous Member

    If you're okay with an output of about 50 watts it'll be fine.
  3. johneck
    Joined: Nov 2011
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    Location: New England

    johneck Senior Member

    Propellers will be much more efficient and given the low power available (no offense intended) you need to maximize efficiency to go very fast. Waterjet come into play for high speeds and high power density. It is hard to beat a well designed propeller at 5 kts.
  4. tunnels

    tunnels Previous Member

    You need to go look closely at a jet ski !! how much horse power can a person produce peddling his little heart out at full peddle ?? and for how long ?? take the weight of a person the Jet ski and the hp it needs to do what it does !! :?:
    A water jet is not very efficent for pushing anykind of boat and need lots horse power :D:p!!!
  5. Petros
    Joined: Oct 2007
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    Petros Senior Member

    many years ago when I was an engineering student I was on a team that developed some bicycles used by the US Olympic cycling team. We did a lot of tests and did research on human powered vehicle such as human powered flight (Crammer prize won by Dr. Paul McCready's team), and met with Dr. McCready in fact.

    A human in reasonably good shape can sustain an output of about 1/4 hp, and can put out peak hp of about 1/2 for short bursts. That is not much to drive a jet. Athletes can put out much more, but I do not think it would be very practical for your average recreational user if you designed it for more.

    The most efficient drive for low hp would be a very slow, large dia propeller. Very large props are not practical for marine use, so you must compromise with 8 to 12 dia max.

    Jets are not efficient at low speeds, but at high hp they prevent blade cavitation, tip losses, and other losses when trying to put lots of power into a prop. Consider that no boat that uses a jet does so for economy, are use very large amount of power (and fuel). It can be done for the sake of being unique, but you would go further with less effort with propeller designed specifically for very low power and low speed operation.

    Good luck.
  6. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    A more efficient jet drive at least for humans is a bellows approach similar to a heart, or a squid or octopus. An you can operate with your legs pressing down and a spring to bring it back. A one way valve would be needed. Your not going to go very fast but you will be generating thrust.
    JamesG123 likes this.
  7. bluekayak
    Joined: Mar 2006
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    Location: Menlo Park, California

    bluekayak Junior Member

    Thanks everyone who answered

    Pretty much what I suspected: if it could've been done, it would've been done

    Reading about jet propelled surf boards got me going

    Nice to have technically-oriented people around to straighten the rest of us out when we get dreamy ideas
  8. Submarine Tom

    Submarine Tom Previous Member

    I think your term sums it up:

    Utterly impractical.
  9. Thomas Grigal
    Joined: Aug 2018
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    Location: Traverse City MI

    Thomas Grigal New Member

    Not so fast...(pun intended) look here>>>> Pedal Boat - JET WAVE Jet Boat https://nmi.craigslist.org/boa/d/pedal-boat-jet-wave-jet-boat/6671829391.html

  10. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell . . . _ _ _ . . . _ _ _

    HP?! About 1/4 of a HP with both occupants pedalling steadily.
    But at the jet you lose 50% so 1/8 of a HP!!
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