Jet powered catamaran

Discussion in 'Boat Design' started by SPJ yachts, Aug 2, 2013.

  1. SPJ yachts
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    SPJ yachts Junior Member

    It been a while sine I've been on the forum but I have noticed from time to time there are questions regarding water jets in catamarans.

    To be more specific, small power catamarans of 6 meters or so.

    After much researching could not find anything, any where that would suit our criteria

    So we started working on a design for a rescue and recovery vessel that would suit civil and military applications and the recreational market as a follow on.

    Resulting in a boat that can operate in extremely shallow water, stable, can run in flood waters with out any issues with submerged objects, working floor area completely clear except for a offset control console, and capable of 120Km/h + depending on the power plant.

    This boat will be prototyped and offered up for assessment to rescue organizations

    The design is still in final stages when available I will post a drawing
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    120 km/hr ????????? Sounds more like a conveyance to escape lawful justice ! :eek: :p
     
  3. TANSL
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    TANSL Senior Member

    SPJ,
    120 km / h .... Amazing¡¡¡¡¡
    Without seeing the project is difficult to say but I think the hulls of a catamaran 6 m in length, with very small breadth, as required for that speed, do not have enough space to house the engines. I wish, for your sake, be wrong.
     
  4. Village_Idiot
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    Village_Idiot Senior Member

    I am assuming you are using twin outboards, one per sponson, with a shallow jet tunnel in each sponson to get the jet foot above the bottom of the hull. Otherwise, the airboats will outrun you! :p

    A single jet in between the sponsons would be counterproductive as the jet foot would need to be low enough to reduce cavitation blowout, thus increasing your draft to where a good prop would run more efficiently.

    My tunnel boat with four-blade prop will run in 6" water depth, but it is 5m and only runs 40mph with a 115hp four-stroke. A good tunnel boat with correct setup can run in 4" of water with a propeller, but those boats are a little lighter and won't carry the weight or have the stability you need and still run that shallow.
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

  6. SPJ yachts
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    SPJ yachts Junior Member

  7. Mr Efficiency
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    Mr Efficiency Senior Member

    He's talking about a catamaran, and I assume using inboard engines. I have seen a cat in the 6-7 metre range that had twin 6-cylinder in line petrol engines with jet drives, could not have been much room at all in there for them. I heard the fuel bill was daunting.
     
  8. SPJ yachts
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    SPJ yachts Junior Member

    Thanks for your comment there are indeed one jet unit and engine per sponson.
    Vessel is designed partly around the engines and jet drive intakes, this is how we have managed to accommodate a powerfull and compact drive system into this boat.
     
  9. SPJ yachts
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    SPJ yachts Junior Member

    Highly efficient DFI petrol 4s engines fit well in each sponson and are below the wing deck. Fuel burn in this application not known but projected (using dyno results) as good as, or better than, similar size 4 stroke O/Bs
     
  10. TANSL
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    TANSL Senior Member

    It would be nice to have a picture of the project because, accepting that there is room for the motors, do you there for fuel tanks?. The power required for such high speed resulting in a high fuel consumption. A rescue boat must have a lot of autonomy. How have you solved the problem of the tanks?
     
  11. El_Guero

    El_Guero Previous Member

    How did you improve the efficiency of petrol engines?

    This I want to know.

    Save me money at the gas pump, please.
     
  12. TANSL
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    TANSL Senior Member

    At that speed, the blows of the waves on the wet deck, at the bow, and the pressure surge that occurs, are able to destroy any structure that has not been designed specifically to withstand these stresses. Have you considered these efforts?. Have you considered the accelerations that occur?. The crew must wear helmets and seat belts, not to mention the seat anchorage to the deck. Have you taken into account the code for high speed craft?
    We will have to do something so that the boat does not start flying. Like I said, it would be good to see something of the project, not to think that it is a pure vagary.
     
  13. rasorinc
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    rasorinc Senior Member

    With a cat hull (2 sponsons) there is a lot of possibilities of getting hung up on rocks and not being able to power up and over. You can get locked in between the sponsons. Also this area needs to be beefed up big time because most are designed for wave slap not sliding off of sharp rocks.
    Just some info for you.
     
  14. messabout
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    messabout Senior Member

    Ad Hocs link to Dart NZ shows a spectacular scene of the rarest natural beauty. Right in the middle of that splendor is a noisy, splashy, speeding, boat likely occupied by noisy, , mindless, people.. Shameful.

    The other two links merely illustrate our collective madness. Ripping around so close to all those rocks seems unnecessarily, and foolishly, dangerous. We humans are apparently willing to pay dearly for a thrill.

    Rant finished.
     

  15. SPJ yachts
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    SPJ yachts Junior Member

    The tankage is also below the wing deck and amidships, and are adequate to keep the vessel in operation as long as necessary. engine/jet unit and fuel tanks are positioned for best trim . CG & CB are at best optimum possible.

    Regarding the speed of the boat, while 120kms is possible its not the main objective of this design. As initially posted this is primarily a rescue vessel and top speed ,although important to be rapidly on station, is not the first consideration.

    Operation in areas where conventional propeller driven vessels would be impossible or at best at low speed with O/B at an attitude that renders steering and control very limited, this is where this boat will be deployed.

    Sponson design is asymmetrical and jet intake/recess with uninterrupted water flow in planning panel keel sections protected with sacrificial HDPE for repeated impact of debris etc.
     
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