Out-of-the-box cheap inboard solution design

Discussion in 'Boat Design' started by preventec47, Aug 7, 2016.

  1. preventec47
    Joined: Jul 2016
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    preventec47 Junior Member

    I am seeing a great availability of used "industrial" motors from Briggs Stratton, Kohler, Honda etc. between 8hp and 30hp and other
    than paddle wheel drives I am not seeing any cheap easy solutions to get thrust from my preferred source......spinning propellers .
    We need to rob cheap stuff off the shelf like drive shafts from cars and their U-joints or the mechanisms from front wheel drive
    cars.... I think referred to as CVS ( constant velocity shaft?) . Also how bout centrifugal clutches used in go-karts and
    maybe chain drive and sprockets and GoKart rear axles sticking through the transom with props connected to the wheel
    hubs etc etc.

    If we can figure out how to do this with perhaps scavenged parts off cars etc we can have complete prop propelled water
    vehicles for hundreds of dollars instead of tens of thousands of dollars. Sure this stuff wont be "Marine-ized" but always
    pulling it out of the water after use and slathering of oil and grease on the critical parts should slow the corrosion
    down. We have to get creative! What are your thoughts ? I am not familiar with the old days but how did
    the early pioneers build inboard shaft drive units ?
     
  2. gonzo
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    gonzo Senior Member

    Look at a sterndrive. The shaft and u-joint are automotive. It's already been done
     
  3. preventec47
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    preventec47 Junior Member

    Wha ???

    Are you saying I can get a stern drive and hook it up to a Briggs and Stratton ?

    How much does that cost ? Isn't a Stern Drive what they used to call Inboard/Outboards

    More expensive than an outboard engine setup right ?
     
  4. goodwilltoall
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    goodwilltoall Senior Member

    How bout putting a tractor unit right in the middle of the boat and connecting rear axles to paddlewheels. U can leave seat just figure height for paddle wheel and enough room to see over. Heavy duty transmission with plenty of gear options and even locking wheels for turning the boat (forgot what that option is called).
     
  5. Squidly-Diddly
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    Squidly-Diddly Senior Member

    two pretty well sorted practices come to mind:

    Thailand's famous "long tail" boats which use a variety of engine sizes.

    Wharram cat design that dangles the motor between the hulls, and looks pretty similar to Thai long boat idea, just in a different position and for a more seaworthy boat.

    I'm pretty sure a Thai long boat engine mount would be a long way from passing muster in any waters outside the 3rd World, and it wouldn't surprise me if their use doesn't have a horrific, non-reported, accident rate.
     
  6. SamSam
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    SamSam Senior Member

    Marinizing is mainly concerned with fire and explosion proofing, I don't think it has anything to do with lubrication. Slathering on lubricants and leaving a trail of oil sheen on the water may draw attention.

    Have you seen this subsection of the 'Propulsion' forum?
    http://www.boatdesign.net/forums/diy-marinizing/


    .
     
  7. gonzo
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    gonzo Senior Member

    You want to build a unit yourself, so look at the gears, shafts, u-joints, etc on a sterndrive. They are no basic differences from any automotive gears, shafts, u-joints,etc. The thrust bearings are necessary to take the thrust of the propeller. It has already been done. You pay thousands of dollars for a unit that is already assembled, properly engineered, extensively tested, warrantied by a reputable company, and actually works.
     
  8. preventec47
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    preventec47 Junior Member

    It doesnt appear the guys racing the CrabSkiffs felt the need to build a stern drive.

    I want to pay dozens of dollars not the thousands of dollars you mention.
     
  9. PAR
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    PAR Yacht Designer/Builder

    Nothing about boating is particularly cheap, especially if you're experimenting with stuff. The solutions the skiff racers have come up with, are based on decades of experence, lots of catastrophic failures, lots of spare parts from previous attempts at something, sinkings, fires, serious mechanical aptitude, etc. Simply put, these guys have fiddled with things, tweaking as they've gone along, until they started winning races.

    There's no free lunch, you have to break some parts to learn what isn't going to work, before you can conjure up something that just might work. For every "good idea" you'll run straight through a few dozen failures first. You don't know you need a thrust bearing on the output end, until you burn through a couple of tail shafts first. This is the hit or miss way, otherwise, you have to do the math, which only provides you with a fair bit fewer catastrophic failures, before nailing it down. Experience is little more than the compilation of your prior errors.
     
  10. gonzo
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    gonzo Senior Member

    I never mentioned price, only that most marine units are based on automotive parts. If you only have dozens of dollars, your project won't get off the ground. Skiff racers, like drag racers, spend every cent they have and borrow a few to get their boats going.
     
  11. FAST FRED
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    FAST FRED Senior Member

    For a low power boat gas tiller motors can be had with usually a 6-1 reduction gearing that could swing a big prop.

    With 6-1 at idle the lack of a clutch or reverse would not be noticed.
     
  12. SamSam
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    SamSam Senior Member

  13. Petros
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    Petros Senior Member

    there is a lengthy thread in this forum about converting a string trimmer engine to use as an outboard. the long shaft is already in place, you just need to find a reliable way to attache a prop on the end, and find a good way to mount the assembly on the transom.
     
  14. gonzo
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    gonzo Senior Member

    If you have the time to tinker, used outboards can be had for free. It will be cheaper and a better finished product to simply overhaul one.
     

  15. preventec47
    Joined: Jul 2016
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    preventec47 Junior Member

    Respectfully Paul while you are quite the philosopher as well as accomplished
    boat designer, sometimes there is a greatly discounted lunch if not completely free...
    mostly thanks to guys like you in these forums and the modern technology that lets
    us talk and share info so easily.

    I realize you are a professional and this is how you generate some income
    and when the time comes I would pay you for some hull plans you have already
    shown me in another thread but does not appear on your website.

    I would also pay you for plans or instructions as to how to assemble the
    complete inboard solution equivalent to the CrabSkiff racers. I just need
    to know in advance what the costs will be so I can determine whether it
    is affordable or whether I need to keep searching for alternative
    cheaper approaches.

    Lets face it guys .... many are here because we do not want to reinvent the
    wheel all by ourselves every single time. Some are doing it, some have done it,
    some have seen it done or something similar and some like to
    dream and prepare for the day that they might be able to do it and some
    just like share their wisdom/opinions regardless of how authentic
    and for which talking about doing it is the closest they will ever come
    to doing it.

    Back to the objective at hand.... While there must have been hundreds
    or thousands over the last hundred years worldwide that have put together
    relatively low powered inboard boats... lets drift to the low hanging
    fruit and that would be the CrabSkiff racers. The jury is out as to
    any authoritative summation of what they are doing. It is hard to
    track the guys down and I dont always have a lot of time to do the
    detective work. Further we dont know whether they are all doing
    the same thing or whether different racers have arrived at different solutions.

    There must be someone locally involved in the crab skiffs... ( you would think
    any one of the racers who have built a boat ) that would be
    expert in the techniques and components used to build those racers.

    So in a nutshell, I believe we can ride their coattails as far as development
    work goes,, the big question is whether we can afford to ride their coattails.

    What is not apparent so far is whether they want to share free or for fee
    their learned knowledge. I will be pursuing it until I get closer to some answers.
     
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