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Thread: Why twin outboards?

  1. #1
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    Default Why twin outboards?

    I saw a design by Aitkin called the Jog-along. It has 2 small (18hp) outboards. Why not just one 30hp? would'nt that be better on fuel and maintnence? also, on a larger application do the outboards need to be counter-rotating? What does counter-rotating do for the design anyway? Thanks, John
    Last edited by Layzboy2011; 06-04-2010 at 10:33 PM. Reason: picture

  2. #2
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    Default Re: Why twin outboards?

    Why stop at 2 ?



    Sorry , I couldn't resist ...back to normal programming .
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  3. #3
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    Default Re: Why twin outboards?

    I would guess that Mr Atkin designed it that way for several reasons.

    1) The physical size of the two motors in profile is smaller than one big one and lends itself to fitting in a smaller well and the enclosure does not need to be as tall.

    2) easier maneuvering at the dock because the motors can be run in opposite directions to pretty much turn on the spot.

    3) and most of all, dependability. The chance of both outboards breaking down at the same time is pretty slim and you could always get back to the dock with just one.

    Modern outboards are smaller, lighter, and more dependable. Therefore, these advantages may not be so relevant today, but still good points to consider.
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  4. #4
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    Default Re: Why twin outboards?

    There is also times when it is favorable to run on a single outboard when you don't need much power. Trolling for fish perhaps, tending traps or nets or where a lot of idling time might be more efficient with a smaller outboard over running a 35 at idle.

    I figure redundancy is the most likely reason though.

    Counter rotation helps alleviate the hull listing to one side from the throw of the propellers and it is much easier to steer. Otherwise, you would constantly have to make corrections with keeping the boat on course with twins with like rotation. On some more tender footed hulls, a single outboard can cause listing regardless and a dual, counter rotating setup can remove this condition.
    Last edited by pipefitter; 06-04-2010 at 11:31 PM.

  5. #5
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    Default Re: Why twin outboards?

    Perhaps back when the boat was designed, you couldn't get bigger motors.
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  6. #6
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    Default Re: Why twin outboards?

    Does it make sense today to run twins? Or is a single the way to go? I am not really looking at building this design, it is more of an academic question.

  7. #7
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    Default Re: Why twin outboards?

    That's a question around a boat load of variables. If you do mostly coastal or inshore cruising, probably not. A VHF radio and a membership with Sea Tow go a long way towards redundancy. If you venture offshore frequently or spend days at a time offshore, sure. I can think of twice that we limped home on one out of two motors. There is things on these new electronically controlled motors that you can't diagnose or correct with a crescent wrench and a screw driver.

    Sometimes an equal hp larger motor is not the most efficient. Take the older OMC 235 hp. Two 115 hp v4's were more efficient and labored less turning two screws and would run pretty much forever. The 235 was often labeled the "too thirsty five".

  8. #8
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    Default Re: Why twin outboards?

    Modern outboards are incredibly reliable, but getting stuck miles offshore with a dead motor, no sails, and a boat that cannot be rowed is not a good thing.

    One large outboard and a small kicker is a very workable option. The weight-to-power ratio is better, and you always have that small kicker for trolling, or for use on a smaller boat. And two matched motors will usually cost more than a single large motor plus a kicker.

  9. #9
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    Default Re: Why twin outboards?

    Quote Originally Posted by Layzboy2011 View Post
    Does it make sense today to run twins? Or is a single the way to go? I am not really looking at building this design, it is more of an academic question.
    When you are WAY OUT there and your motor makes a weird noise, you will KNOW WHY two engines are better than one. You won't argue.
    Have separate fuel supply to each engine also.
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  10. #10
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    Default Re: Why twin outboards?

    Most of the problems relate to the fuel and electrics. Unless these are also redundant, dual outboards don't offer a lot more reliability than a single. I advocate one adequately sized engine and a smaller kicker when that is needed for either real or imagined increase in reliability. On a fishing boat, I have used one large engine for most of the time and a small one for trolling or puttering along. Saved a lot of fuel and fouled plugs on old two strokes.
    Tom L

  11. #11
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    Default Re: Why twin outboards?

    how much maneuverability is there to be gained by going with twins? this seem like the biggest advantage (assuming a kicker motor) I am thinking a 30' boat or so...

  12. #12
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    Default Re: Why twin outboards?

    Outboards are mounted closer together --24 inches on center is typical--or just enough so the cowlings can be removed from either-- so they don't provide the same ability to spin a boat as twin inboards. Being aft of the transom, instead of forward, also weakens their usefulness in close quarters, compared to inboards. But for all that, you can oppose the two engines and enhance your maneuverability around the dock to a point that's better than just one OB. Power cats are an exception.

    Kevin
    Last edited by Breakaway; 06-05-2010 at 10:45 PM. Reason: spelling
    There are two kinds of boaters: those who have run aground, and those who lie about it.

  13. #13
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    Default Re: Why twin outboards?

    On the other hand, having two engines means there is twice as much chance of having one break down, Hence, having a spare is more important for the twin-engined craft as for the single.

  14. #14
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    Default Re: Why twin outboards?

    Quote Originally Posted by phiil View Post
    On the other hand, having two engines means there is twice as much chance of having one break down, Hence, having a spare is more important for the twin-engined craft as for the single.
    Huh? Try that reasoning with the twin engined commercial pilots. Not that they have the option of a little 'get you home ' kicker

  15. #15
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    Default Re: Why twin outboards?

    Some means of getting home when your single main engine flunks is necessary.
    Sail works... sometimes oars or a kite will help... so does a friend who can tow you in... but usually, all of us would feel better with a small engine backup. This can be a lightweight in a locker, saved only for that unwanted time.

  16. #16
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    Default Re: Why twin outboards?

    Looking at the description and drawings, the twins are probably for the "go out in any weather"; they're fixed, props inside the transom, skeg between the props according to the text to protect them from grounding. I would think that contra-rotating props would be in order for rough seas? (The one in the photo seems to have an inboard-outboard drive, or an early i/o water-jet?)

  17. #17
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    Default Re: Why twin outboards?

    Oh...BTW..no maker I know of makes counter rotating engines in small HP. Just 150 and up, nominally.
    There are two kinds of boaters: those who have run aground, and those who lie about it.

  18. #18
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    Default Re: Why twin outboards?

    Small diameter props of outboards don't have the torque issues of their larger brothers. For instance, a pair of Honda 35's on a small 15 foot boat showed no noticeable torque problem with both having right hand props. The off center thrust with one of them tilted was not a problem either.
    Tom L

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