9' x 30' cat hull with 2 different HP engines?

Discussion in 'Outboards' started by rasorinc, Feb 15, 2012.

  1. rasorinc
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    rasorinc Senior Member

    Does anyone have experience with 2 different HP engines at the end of the 2 sponsons be it outboards or inboards?
    I'm thinking of a 60-75 hp outboard on one sponson and a 9.9-20 hp kicker on the other both high thrust with 2.33 to 1 gearing. They would not necessarly run together. Affects of torque and the steering problems concern me. Would like to know if this can be done effectivly and with out hazard.
    Many thanks because if this can be done I can save lots of dollars. Speed is not going to be a problem, fuel efficiency IS my goal.
     
  2. Stumble
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    Stumble Senior Member

    Go with twin 30-40 hp instead of a kicker and the bigger engine. The torque on the boat will be substantial if you use have one engine operating, causing you to oversteer to correct, and hurting fuel economy. Not to mention placing torsional loads on parts not designed for them.
     
  3. Richard Woods
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    Richard Woods Woods Designs

    I agree, and another major problem will be manouvering with one big offset engine, because of the prop kick

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  4. CatBuilder

    CatBuilder Previous Member

    Now, I am not following this. For fuel efficiency, we catamaran owners always run a single engine in a single hull when out in clear, open water and motoring for long distances.

    What is the difference between doing that and doing what Rasorinc suggests?

    How would there be a problem with torque on the boat and oversteering? I've never had those problems on other catamarans even when using a single inboard engine with the other engine off, creating drag in the non-powered hull.

    And why would there be problems maneuvering?

    Wouldn't you just pop that big engine into gear at idle and do the same with the 9.9, but give it a touch more throttle as you do so, worst case?

    I'm not trying to start a huge debate, but I can't see the issues here. I can't see how these problems mentioned would arise.

    Glad to be educated though. :)
     
  5. rasorinc
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    rasorinc Senior Member

    Thank you for your replies. I would sure like to get a few more opinions on this subject
    I understand torque pull and steering variables. I can build a center short sponson for 1 large outboard with a 9.9 to one side or the other, but that is a lot of extra work and weight. Not concerned about high speed but do want it to get on plane(it is a planning
    boat.) Thanks again.
     
  6. keysdisease
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    keysdisease Senior Member

    MacGregor 36's had just one outboard on one hull, you had to adjust for the asymetric power when manuevering, otherwise they worked fine.

    Steve
     
  7. Richard Woods
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    Richard Woods Woods Designs

    You can run one engine at displacement speeds on passage without problems. It's certainly the most efficient way to motor.

    But you will probably have problems manouvering. Years ago I delivered a 43ft catamaran from the UK to the Canaries. It had twin inboard engines (27hp each?) One failed en route. We could motor at sea at 6 knots with the remaining engine. But it was nightmare getting into the marina in the Canaries. We ended up reversing in as the boat would not turn to port AT ALL at low speeds

    I would think it was unwise to go at high speeds with an offset engine, but I have never tried it so cannot really comment.

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  8. mydauphin
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    mydauphin Senior Member

    Would you put smaller tires on one side of a car. Most twin boats don't work that well on one engine, and the farther apart the worst it must be.
     
  9. CatBuilder

    CatBuilder Previous Member

    That is an invalid comparison.

    I run my catamarans on a single engine all the time. My experiences differ from Richard's in that I am able to dock, pick up moorings or go to anchor on a single engine as well. (I wonder if it was just that particular boat... or my particular boat?

    I had some junk in my tanks and it would plug the fuel filters on occasion one season. When it happened, I just ran the other engine to get in, then changed the fuel filter at my leisure.

    There was no issue handling. Catamarans work just fine with a single engine in one hull.

    The thing I'm having a hard time understanding is if a catamaran works just fine with one engine, why not 1.5 engines? or 1.3 engines?

    If you have a large engine on one side and are put putting around the docks (only place you need two engines), wouldn't you just start up the smaller engines and use that as well as the larger to pivot the boat around?

    Seems nobody has tried it, which is why nobody can tell for sure if it works or not.

    Of course, I am only talking about displacement boats... it seems it would certainly make a big difference in a power cat or planing boat.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    A single engine (one side) on a cat works well enough in open water, clearly close quarter manoeuvres are problematical. Also, rough water can create problems with tracking, but it will always be more economical to run on one engine, provided it is not being over-worked to maintain the desired speed.
     
  11. mydauphin
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    mydauphin Senior Member

    I think it will work on a lightly loaded CAT, if the hulls are heavy or have a bigger draft then it will drag. Even on a monohull with one engine next to the other you have to turn the wheel to compensate.
     
  12. Richard Woods
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    Richard Woods Woods Designs

    To Catbuilder

    It maybe because your old boat was heavy and narrow with deep hulls and maybe had big engines

    The boat I sailed to the Canaries was more like your new boat. Wide light and shallow

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  13. CatBuilder

    CatBuilder Previous Member


    Good thought, Richard. That may be it.
     
  14. rasorinc
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    rasorinc Senior Member

    Thank you all for your comments. I REALLY APPRECIATE IT.
     

  15. hamed gwd
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    hamed gwd Junior Member

    :idea:Good replies
     
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