Jet DIY

Discussion in 'Jet Drives' started by Duco84, May 19, 2022.

  1. Duco84
    Joined: Feb 2014
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    Duco84 Junior Member

    It is my cousin project. He made all himself, but unfortunately results are not as expecting. Now we will try to make new, but we need more details. Does someone has dimensions of jet for similar power and rpm?
     
  2. anthony goodson
    Joined: Mar 2007
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    anthony goodson Senior Member

    Well you can source these details from manufacturers brochures. Hamilton jet's website will give you all that information ,that's the easy part, but that won't mean you can make a working jet. You need to research the subject in greater detail , before you BEGIN to make anything. I admire your cousin for trying ,there are not enough people out there with that mindset these days ,but at the moment it is clear that he has a lot to learn, but all the information is out there on the internet If he is really keen to do this it is not impossible just a bit more difficult than it looks. Twenty years ago I was curious as to whether I could produce a working jet unit in my garage for my own use I took the best ideas from those available at the time added a few tweaks of my own and ended up making three , I am pleased to say they are all still in use in my family today. So be positive ,and good luck.
     
  3. Duco84
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    Duco84 Junior Member

    Thank you but I couldn’t find. Please send link.
     
  4. anthony goodson
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    anthony goodson Senior Member

    Good morning Duco,there isn't a link that will solve all your problems ,The best advice that I can give you for what it's worth is to type Waterjet Propulsion into google and research from there ,all the information ,photographs etc that you need are available . If having done that you have any more specific questions then please return here ,or if you wish pm me. Others on here may have a better idea.
     
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  5. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell . . . . .

    Duco84,

    Is it a catamaran?
    Any more hull pictures?
    Have you found any replies helpful here on your thread?

    Have you graphed resistance/speed?
    What is your target speed?
    What will the total boat weight be when loaded?

    Sorry, so many questions (6) but we need more information.
     
  6. Duco84
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    Duco84 Junior Member

    No it is monohull. Unfortunately I didn’t find any useable info. I think 12kn is reasonable speed, in any case to load engines. (Maybe to make new inlet and play with nozzle dimensions? Total load weight is abt 2.5 t.
     
  7. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    The first step should be to modify the bottom of the boat so the water flow improves. Those humps and sharp transition will create turbulence and probably ventilate also. Once you have a hull bottom designed and built for a jet drive, you can start the jet design.
     
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  8. Duco84
    Joined: Feb 2014
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    Duco84 Junior Member

    Yes I know, but at this moment I have this, and I want to help only to change jets in order to load engines and try to achieve a higher speed. I hope that changing of inlet and other size of nozzle will help.
     
  9. baeckmo
    Joined: Jun 2009
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    Location: Sweden

    baeckmo Hydrodynamics

    In order to arrive at a reasonable figure for the jet size, you have to know the exact weight of the boat, empty and loaded. In this thread you have mentioned weight as "about 2,5 tons", and earlier you gave a figure of 2,7 tons, which tells me that you are just guessing. The line between success and failure is very thin in this case, there is no chance to make it functional without facts. You must realize that the junk attached to the boat's transom has to go away, all of it! It isn't even close to what it should look like. There is no chance that simple changes of impeller or nozzle size can compensate for that.

    I understand that you want to build your own jet units. The questions then are what resources in terms of financing and mechanical workshop equipment you have available, and to what extent you can apply instructions from qualified forum members with jet knowledge. Please forgive me for a spoonful of patronizing, but jets are tricky creatures to design, so if you really want to do this, it can be done, but there are no shortcuts ahead!
     
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  10. BlueBell
    Joined: May 2017
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    BlueBell . . . . .

    Props instead of jets would be a whole lot easier.
    Surface drives.
    What's the bottom where you run shallow, gravel, sand, mud, smooth rock?
     
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  11. Duco84
    Joined: Feb 2014
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    Duco84 Junior Member

    I know all that, the best solution is to buy a new boat, but I want to try. I said Weight is 2.5t, and width of wl is 2.7m.

    plese if anyone know dimensions of jet installed on similar power engines
     
    Last edited: May 25, 2022
  12. baeckmo
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    baeckmo Hydrodynamics

    You're right, my misreading. Now, it is not the engine power that drives the jet dimensioning here, but the thrust required to push your hull past the hump speed. Key factors are the weight/power ratio and slenderness ratio. Without deeper info on your hull (bottom shape, spray rails size and position, center of mass et c) I would say that you will need impellers with inlet diameters between 220 and 240 mm combined with nozzles between 125 and 145 mm, all referring to jet units with correct design of inlet housing and stator. If you could arrange a step-down gearing with a ratio around ~1.25:1, you would have less cavitation problems, though, but you know all that as well I guess...........
     
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  13. Duco84
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    Duco84 Junior Member

    Thank You, I appreciate.
     
  14. anthony goodson
    Joined: Mar 2007
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    anthony goodson Senior Member

    This jet is powered by a 2litre turbo diesel engine the mixed flow impeller is 270mm diameter and the nozzle diameter is 150mm WP_20181024_16_41_12_Pro.jpg WP_20181024_16_40_16_Pro.jpg
     

  15. BlueBell
    Joined: May 2017
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    BlueBell . . . . .

    You have the hull, measure drag at speed and graph it.
     
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