School me on jets. Looking for something that may not exist

Discussion in 'Jet Drives' started by curtis73, Oct 3, 2021.

  1. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,401
    Likes: 1,034, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    I'd have sworn they were centrifugal Barry.
     
  2. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,401
    Likes: 1,034, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Fit this with an inboard jet, and that will be quite a bit of work too, and go motoring on this shallow, rocky river, and the destruction of the whole thing is inevitable, would you take a jet ski through there ? Of course not, and they are a lot heavier built than this thing. If it was 6mm alloy plate bottom, you might get away with the jet, the glass is bound to suffer a fiasco
     
    bajansailor likes this.
  3. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,401
    Likes: 1,034, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    One possibility, if this was a monohull, might have been a "shoe" along the centreline to take the groundings, but you could easily bottom on the outside sponsons, they are pretty well the same depth
     
  4. Barry
    Joined: Mar 2002
    Posts: 1,607
    Likes: 355, Points: 83, Legacy Rep: 158

    Barry Senior Member

    Back in the early 80's a friend had a 15 hp outboard pushing a 12 foot lund rivetted aluminum boat. It would push about 500 pounds of gear up fast moving water. Attached to the ventilation plate was a Riffle Runner, which looked like a tunnel.
    I have not seen another since though a quick image Google search will bring them up. The motor had to be installed higher than normal and very little of the lower case was below the bottom of the boat. Some but minimal
     
  5. ondarvr
    Joined: Dec 2005
    Posts: 2,795
    Likes: 483, Points: 83, Legacy Rep: 506
    Location: Monroe WA

    ondarvr Senior Member

    I have a riffle runner someplace, never used it.
     
  6. Barry
    Joined: Mar 2002
    Posts: 1,607
    Likes: 355, Points: 83, Legacy Rep: 158

    Barry Senior Member

    I am referring to the pump that most outboard OEMs use, built by Specialty Marine/Outboard Jets in California. A radial/centrifugal flow impeller has the inlet coming into the center area of the impeller, the water is accelerated radially to the edge of the pump housing then out to an outlet. Generally, centrifugal pumps are high pressure low volume. (there are also open face centrifugal impellers as well)
    Mixed flow impellers, Berkley, American Turbine, medium volume medium pressure and then axial pumps, older Hamilton 77x series, Kodiak . (the new Hamiltons are said to be more axial in flow configuration (212 series for the 18 - 26 foot range)

    The third picture down is a picture of the impeller from a Specialty Marine/Outboard Jet.



    [​IMG]

    Centrifugal above


    [​IMG]


    l[​IMG]

    Axial above

    [​IMG]
    Mixed
     
  7. bajansailor
    Joined: Oct 2007
    Posts: 2,743
    Likes: 1,051, Points: 113, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    DogCavalry likes this.
  8. curtis73
    Joined: Mar 2002
    Posts: 80
    Likes: 1, Points: 8, Legacy Rep: 14
    Location: Variable, North America

    curtis73 Junior Member

    Agreed. As of yet, I have not found a smaller unit than 500cc, at least not in the common brands of PWCs

    I'm after planing and being able to lift one end in the boat in a van or truck bed, then hoisting the other end and sliding it in. I'm also after not occupying half of the boat with a drive unit.
     
  9. baeckmo
    Joined: Jun 2009
    Posts: 1,363
    Likes: 339, Points: 83, Legacy Rep: 1165
    Location: Sweden

    baeckmo Hydrodynamics

    The jet pump power is proportional to shaft rpms^3. There are wrecked PWC's around, get your hands on one of the smaller units (~6" inlet diameter) and match it to an engine with a suitable power/rpm range, simple.....
     
    Ad Hoc likes this.
  10. curtis73
    Joined: Mar 2002
    Posts: 80
    Likes: 1, Points: 8, Legacy Rep: 14
    Location: Variable, North America

    curtis73 Junior Member

    YES! This is exactly what I want. A poorly-performing Jet Ski. Bingo. Now we're getting somewhere.

    This is a 4' x 8' boat. A) I don't have to move around. I sit and fish. B) standing up in this tiny bucket is not really an option without falling in the drink anyway. Look at my last picture. The red box would more than adequately house a GY6 and a small jet pump with room left over for life jackets, a gas tank, and the required safety equipment. The middle seat is coming out anyway and the front platform is getting extended. Divinycell is being selected and the vacuum bags are ready. In fact, all said and done, the red box idea combined with removing the center seat may increase space in the boat.

    I really appreciate the thoughts, but the smallest/lightest outboard jet I've found is a 25hp head/15-ish hp output and $4000. A 25 hp outboard plus the weight of the centrifugal drive is just insane on this tiny tub. They weigh 150+ lbs, and I weigh 225. Until I put me with clothes, 3 gallons of gas, and the jet outboard on the vessel, we're looking at 400 lbs. It just won't float. It would also mean me mounting and un-mounting the heavy beast every time I want to take it out. In contrast, a GY6 weighs 30 lbs and is the size of a sewing machine. Not to mention easily available for free in hundreds of broken scooters on FBM, and even if I bought a brand new one, it's $250.

    The ONLY way I would consider a jet outboard is if you found one that puts 10 hp to the water and weighed 50 lbs or less, and to the best of my knowledge, it doesn't exist.

    I guess I'm confused as to why many of you are suggesting an outboard that is massive and steering me away from some kind of inboard jet. Care to share your reasons, y'all?
     
  11. curtis73
    Joined: Mar 2002
    Posts: 80
    Likes: 1, Points: 8, Legacy Rep: 14
    Location: Variable, North America

    curtis73 Junior Member

    This was a thought, but I don't have the expertise to know if I can effectively re-power a pump originally designed for 500-600cc with a 150-200cc powerplant and not have it be wildly mismatched.
     
  12. comfisherman
    Joined: Apr 2009
    Posts: 230
    Likes: 102, Points: 43, Legacy Rep: 10
    Location: Alaska

    comfisherman Senior Member

    I replied to the thread on the "other boat forum".

    Kawasaki made a 300cc stand up in the late 80s it was the smallest. They also made a 440 and 500. Those will be the smallest physical dimension engines you can find. Goodluck finding a running one, the kawasaki motors were abysmal compared the Yamaha counterparts. There weren't many running ls300 jetskis in the late 80s, cannot imagine many if any still exist. The smallest most popular jet is the Yamaha 650cc out of the super jet stand up. It will likely be to long to work, your hull also wouldn't be the greatest for a jet conversion without some modification.


    There are 75, 100, and 110mm plastic jet units on the various China direct web sites, very little exists in information about how much power they can absorb. A few of the cast aluminum ones used to absorb a 29cc weed eater motor. But something designed for a 20 lbs boat isn't gonna hang pushing a dingy and a dude....

    The mini jet boats are routinely overpowered to compensate for the fact that they are overweight relative to the impeller and engine combos installed.

    Don't think the child's jets skis ever made it to the USA due to emissions compliance, but they look to be about the size of the kawasaki ls300.
     
  13. Barry
    Joined: Mar 2002
    Posts: 1,607
    Likes: 355, Points: 83, Legacy Rep: 158

    Barry Senior Member

    The impeller designed for 500 - 600cc will not be able to be spun up to the same rpm as the your proposed 200cc as the hp due to lack of power.
    But Baeckmo can confirm, The difference between horsepower requirements for the Berkeley pump impellers was the amount of clearance between the impeller and the wear ring. ( to a point) So perhaps this may be possible depending on the
    type of impeller that you end up with
    Ie machine additional clearance and the 200 cc may attain enough rpm to reach its working HP
     
  14. comfisherman
    Joined: Apr 2009
    Posts: 230
    Likes: 102, Points: 43, Legacy Rep: 10
    Location: Alaska

    comfisherman Senior Member

    The impeller is much like a prop, and they can be purchased in different ranges for different applications. It will be hard to find one pitched to work on a 200 cc engine off a jet setup for 700cc. Although it looks like the kawasaki 440/300 pumps can pitch pretty low. Not sure if that would be enough.
     

  15. comfisherman
    Joined: Apr 2009
    Posts: 230
    Likes: 102, Points: 43, Legacy Rep: 10
    Location: Alaska

    comfisherman Senior Member

Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.