Inboard surface drive small boat.

Discussion in 'Surface Drives' started by Greg01, Aug 15, 2022.

  1. Greg01
    Joined: Aug 2022
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    Location: Chattahoochee, FL

    Greg01 Junior Member

    Hello,
    I am glad I found this forum!
    I have a project and a million and one questions.
    My project is a 18' aluminum hull I wish to turn into a inboard surface drive. It was an outboard with a 70hp Evinrude.
    Spent the last 3 days looking for related posts here on the forum. I found several close but not exactly fitting my plan.
    No way could I use fixed shaft and a rudder. I am in the weed infested swamps of north Florida. And venture into the shallows.
    So it has to be a steerable and tilt able shaft. My biggest concern right now is what U joint or CV joint to use, and how to seal hole trough transom?
    The shaft would need to be able to slide on splines I think. To compensate for steering and tilt movement?
    Any information and advise anyone will share will be very appreciated.
    Thanks,
    Greg
     
  2. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Welcome to the forum.
    Having been involved in the design and building of two custom steerable rear propulsion units before; the first question I have to ask is: "Are you a good machinist with a professional shop or have access to one?"
    This is not an endeavor to take on lightly. It took us several months even in a shipyard machine shop.
    FWIW, we used a Honda CV joint and it was steerable only; but was also a CR prop set.
     
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  3. baeckmo
    Joined: Jun 2009
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    Location: Sweden

    baeckmo Hydrodynamics

    Been down that path as well, and can underline the importance of JHM's first question. That said, and with the requirement of tilting added, I found that the double cardan, as used in IO drives, is more forgiving when it comes to the presicion of the swivelling point location. Take a close look at the transom assembly of the Volvo Penta outdrives type AQ 290 (but NOT the SX or Mercruiser variants). There you find the "how-to" both for sealing and dealing with the propulsion forces.

    Generally, the design lifetime for these leasure boat transmissions is very short, compared to the requirements in commercial environments. Given the "normal" annual operating time for a leasure boat, you may probably be able to limit the design life to something like 500 to 800 hours (based on max power rpm and torque). Depending on the torque your'e going to use (remember you will probably have a gearing-down tranny in front of the cardan!), you can most certainly find a suitable double cardan among the various IO models.
     
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  4. Greg01
    Joined: Aug 2022
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    Location: Chattahoochee, FL

    Greg01 Junior Member

    Thank for your response. I am a mechanical engineer very familiar with machining and steel alloys. Trying not to reinvent the wheel, just wondering if there are suitable universal or CV joints that can be used.
    Being a small boat there is no need for lots of horse power. I am looking into small automotive engines between 80 to 150hp. Checked into the drives available and they are for large high horse power boats, Much more than what I need. And very expensive. Or the transom clamp on kits that use lawnmower engines.
    Still in the information gathering stage.
     
  5. Greg01
    Joined: Aug 2022
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    Location: Chattahoochee, FL

    Greg01 Junior Member

    Very helpful information. I haven't checked into transmissions yet. A little surprised at the short life they have. My plan is to use a water cooled gas engine of 80 to 150hp. It will be plenty of power for this boat. Perhaps low hp will easier on the transmission?
    I will take a look at the IO drives, thank you.
     
  6. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    Don't worry about the drive leg as such; it's the arrangement with an inner strut with bearings and a neck for a bellows, seating and sealing in two donut rubber rings (doubling as aft engine mount) that is important. You will have to take the propulsion forces via some kind of gimbal arrangement. This is where the double cardan joint will tolerate more radial and axial displacement than a single CV/Rzeppa joint.

    When/if you check for dimensioning of the joint (CV or cardan), you will find that the suppliers use graphs where joint size and life are functions of torque, speed and operating angle. I have used torque and rpm values with a total average angle of ~8 to 10 degrees for operating life estimates, and the results seem to confirm the principle.
     
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  7. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    This is the important point, where you put the watertight boundary and what is exposed. For longevity of if you really want to go shallow or mudding, you need to protect the running shaft, joints, and thrust bearing. In this case a fully enclosed unit like an Arneson or a torque tube set-up makes more sense but is heavier and more difficult to machine. Otherwise you could have a simple open frame with a typical stern tube at the transom, but all the gear is exposed.
     
  8. OCB
    Joined: Dec 2015
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    Location: USA

    OCB Senior Member

    ("Quote form Greg01 ")
    My biggest concern right now is what U joint or CV joint to use, and how to seal hole trough transom?
    The shaft would need to be able to slide on splines I think. To compensate for steering and tilt movement?
    Any information and advise anyone will share will be very appreciated.

    Welcome to the forum,
    Your biggest concern is valid. The key to that type of surface drive design is the limitation of current CV and u joints. I have spent years doing R&D designing a new type of ball and socket joint that I named the X-joint. The X-joint is capable of handling the high angles, axial and rotational loads. I'm currently have no resources to move forward with inboard drive design. I'm open to working together with the right person to complete the project.


    OCB

    51845EB5-A103-42AE-BA5C-7B9834E9107C.jpeg
     
    Last edited: Aug 19, 2022
  9. comfisherman
    Joined: Apr 2009
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    Location: Alaska

    comfisherman Senior Member

    So your shooting for a static motor and a tilting/steerable tail? Would it be over the stern or through the transom?

    Seems like an 18 foot alloy boat for the Florida swamp is begging for a long tail. About every winter I migrate for two weeks to near lake Seminole and all around that area on a 17 foot sea ark/Grumman. It's a cousins boat and he just went long tail after his umpteenth lower unit post strike. His is a prepackaged unit, but others are building their own. Mostly air cooled pumped up engines but folks have definitely uses small automotive engines. Usually using cheaply acquired outboard tilt and pivot units, allows them to go remote with standard marine steering options if tiller steer isn't needed. Then all you need is to make a static long tail.
     
  10. baeckmo
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    baeckmo Hydrodynamics

    OCB: About your "X-joint": is it homokinetic? It seems to involve sliding elements for torque transfer, how do you lubricate/cool, is the swivel point fixed or sliding in axial direction? If fixed, does it accommodate axial forces?
     
  11. OCB
    Joined: Dec 2015
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    OCB Senior Member

     
  12. OCB
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    OCB Senior Member

    Yes the X-joint is homokinetic with two joints phased correctly. Yes it has sliding elements to transfer torque. I have done testing many different types of ways to lubricate/cool the friction surfaces. It depends on the application. In the design posted the axial swivel is fix between two hafts. Yes it will accommodate high axial forces.

    OCB

    output_E9GB0b (3) (1).gif
     
  13. baeckmo
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    baeckmo Hydrodynamics

    If two joints are needed to cancel angular variation, then it is not a homokinetic device; be careful with your performance statements please!
     
  14. OCB
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    OCB Senior Member

    That's very good advice Baeckmo.
    First let me say I'm not a engineer. No is the correct answer to your question about homokimedic with a single X-joint. When two joint are phased correctly they produce 100% constant velocity.
    With only in house manual testing completed up to this point my data shows single X-joint has a slower rate of oscillation, less time at full oscillation then a single Cardan joint = less vibration. I will have all the correct data after lab testing is completed. The picture is of the AX-90 with 3/4" shaft.
    OCB
    SEMA picture 3 (2).jpg
     
    Last edited: Aug 24, 2022

  15. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    Ok, let's not hijack this thread, we may discuss your joint elsewhere. For now I'd say it is not relevant to the loads in this case.
     
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