Learing inboards

Discussion in 'Boat Design' started by Saqa, Jun 21, 2021.

  1. Saqa
    Joined: Oct 2013
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    Location: Hervey Bay

    Saqa Senior Member

    Hi all
    Looking for help understanding what makes a good inboard motor. I would like to learn about what aspects to look at to help select a range of options

    Light foiling Inflatable Boat 26' length, 2m beam. Total weight of hull, fuel, passengers and load about 700kg (without engine). Target speed 30 knot cruise

    I am attracted to the idea of using a motorcyle engine or a Rotax or even a 13B series engine for light weight. All of these are pretty high rev'ing engines and I wouldn't know the first thing really about what is suitable

    Things like cooling
    Fuel consumption at cruise

    A quick crash course will be very highly appreciated. I have tried looking online but most documented info for small engines are for boats that putter around
     
  2. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Have you had a read through of this (very long!) thread yet?

    Why don't boats have gears? https://www.boatdesign.net/threads/why-dont-boats-have-gears.24747/

    Your best bet might be to look for an 'old' (but hopefully not too knackered) engine out of a jet-ski?
    I think the most powerful ones go up to 1,800 cc - which must be a lot more than the largest motor cycle engine? (I do not know much about motor cycles)
    And a jet-ski engine has the advantage that it has been 'marinised' already for you.
     
  3. Saqa
    Joined: Oct 2013
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    Location: Hervey Bay

    Saqa Senior Member

    Thank you for the link. Trying to digest it

    13B - REW rough specs
    153kg
    250hp @ 6500 rpm
    300nm @ 5000 rpm
     
  4. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    Re-invention of the wheel is hard work, you have enough on your plate without "radical" powering solutions, with the unusual foil assisted inflatable ! In any case, 30 knots is a fast speed to maintain on Hervey Bay, I do not like your chances of hitting the speed-economy-comfort trifecta that has eluded everyone else.
     
  5. Saqa
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    Saqa Senior Member

    You must have some ideas on increasing my chances :D
     
  6. Saqa
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    Location: Hervey Bay

    Saqa Senior Member

  7. Saqa
    Joined: Oct 2013
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    Location: Hervey Bay

    Saqa Senior Member

  8. Saqa
    Joined: Oct 2013
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    Location: Hervey Bay

    Saqa Senior Member

  9. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Don't even think about marinizing engines !
     
  10. Saqa
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    Location: Hervey Bay

    Saqa Senior Member

    I must find a way to decode your one line posts! Maybe I should ask how many bundies would get me on the same page as you: :D
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    marinizing petrol engines leaves little room for mistakes, there being obvious safety implications if it is isn't done properly. Then there is the matter of a marine transmission , too much drama as a one-off exercise.
     
  12. Saqa
    Joined: Oct 2013
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    Location: Hervey Bay

    Saqa Senior Member

    Mr E, do you prefer a world where no one even thinks to tackle any enterprise that has a challenge to surmount? I am commenting on the pattern I see on this site
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    I think the actual boat is challenge enough, and you are far from settled on the detail of that, so I think one thing at a time is the best approach.
     
    clmanges and bajansailor like this.
  14. Saqa
    Joined: Oct 2013
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    Saqa Senior Member

    Do you remember Ad Hoc line of questioning? Which engine, size, weight, will it fit? etc........

    C'mon man, you guys are all making this a chicken or egg thingy!

    Will the engine fit the boat? Will the boat fit the engine? Will the power train be too heavy for the available displacement?

    Bwoy looks up some of the smallest, lightest 100hp+ engines to hope to sneak in a powertrain and is advised to focus on the boat first!

    Either you or Ad Hoc not being logical here
     

  15. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    The boat and motor need to match, I would have thought worrying about selecting an engine before the boat idea has crystallized, is nonsensical. If there was only one engine available, sure, you would have to design the boat to suit the motor, but in this case you want a suitable boat as the goal, not a boat that will match a pre-determined engine, so work up your ideas about the boat first.
     
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