Catamaran Single Engine One Hull

Discussion in 'Multihulls' started by Boatguy30, Jul 20, 2012.

  1. Boatguy30
    Joined: Dec 2011
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    Boatguy30 Senior Member

    Does anyone have any practical experience with a catamaran having one engine on one hull? I realize this works fine offshore as many cats only run one engine whilst on passage. I'm concerned about handling mainly when cruising the intercoastal/ passing other boats, etc.

    I'm building a 34' Wood Vardo and thinking either a pod/sled mounted outboard or maybe 2 small single cylinder diesels. None are currently made so would be second-hand 1GM10 or BMW D7

    I recently did a repower on a Searunner 34 and have the 12hp Westerbeke 12C. That engine is 225 lbs so not too heavy, but don't want two engines that weight. Hence the thoughts about the single engine and possible a electric drive on the other hull of some sort for maneuvering if necessary.

    Any thoughts appreciated. I ran this idea by Richard a while back and he prefers the outboard.
  2. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Handling ? Needless to say, having the one engine on the corner of the boat will turn a lot more readily one way, than the other. Obviously you must also lose a little headway by having to have the line of thrust askew a little to keep running in a straight line.
  3. Frosty

    Frosty Previous Member

    There was/ is a cat been built that claims to have uneven hulls to run on one engine --it has been discussed on these pages.

    My cat will not run one engine. I would not dream of manouverng close without both or even leave the dock with only one. I would not be able to take it out.

    A sailing cat might be different.
  4. Windvang
    Joined: Jan 2006
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    Windvang Yacht Designer

    Farymann has a 7HP single cylinder diesel, also available in saildrive version
  5. Steve W
    Joined: Jul 2004
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    Steve W Senior Member

    I used to own a Macgregor 36 cat with a single 9.9 yamaha on the stbd transom,for the most part it was fine but i had no remotes so i had to operate it from standing on the motor bracket and steering with the tiller bar in front of me when manouvering,also i kept the boat on a mooring and rarely went into marinas so we sailed on/off the mooring mostly. The advantage of an outboard on one transom is that it can be steered,the advantage to the single inboard would be that the prop would be ahead of the rudder.
    Two 9.9s at about 100lbs apiece would be a better bet i think.

  6. Jetboy
    Joined: Feb 2012
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    Jetboy Senior Member

    Could put a small electric trolling motor on the other side for use around the marina. Should be easy to use with a simple fwd or reverse for the times you need it.

    I would think it would be much more manageable to have a single motor on a cat with dagger boards especially if you can pull the one on the side w/o the engine.
  7. rasorinc
    Joined: Nov 2007
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    rasorinc Senior Member

    You could design a short third sponson for the center rear of the cat to direct water to a single outboard engine, then you have no manuvering problems. A kicker engine then could be placed on either of the oudside sponsons. That is my plan for the Glen-L BearCat.
  8. Dryfeet
    Joined: Aug 2010
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    Location: San Juan Islands

    Dryfeet Junior Member

    I've long considered this concept but have been unable to really decide whether I'd really, really do that. My 41' cat handles pretty well on one engine with a bit of planning. I've had no problem getting on a mooring with one engine but a slip or dock would be a touch nerve wracking. Even with two engines, I find that I would really be better able to use a bow thruster in many cases instead.

    I'd recommend a single engine and a single bow thruster if you didn't want a second main engine. There are a few pretty neat, small, retractable ones out that might do the job quite well.

    I also find that I really like the reduncancy of a second engine. I'm less concerned about a failure, or hitting something when I know I have another one around. Re-sale is another issue. I know, I know, you'll never resell it or you don't care (that was my thought anyway) but the cold, hard reality is that it will severely impact your ability to sell when you have something that is way out of the 'norm' and when (not if) you ever decide to sell, your market will be very, very small.
  9. cavalier mk2
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    cavalier mk2 Senior Member

    It would seem to me that any one could install a second motor later for those worried about a boat outside of convention. (its going to be your boat isn't it?) Other options- one engine 2 props with hydraulic drive, or diesel electric with the one engine powering 2 electrics. The battery bank can be in the hull opposite the engine to balance the weight.
  10. Dryfeet
    Joined: Aug 2010
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    Dryfeet Junior Member

    The beauty of the single engine in one hull is that you can counter it in the other with batteries or a generator. Believe me, I think it's a potentially great way to go. Personally, I wouldn't mess with the complication and expense of the diesel-electric or worse yet, hydraulic single engine/two props hassle. I believe the OP is trying to save money because he has a single engine available to him.

    The only caveat I'm really making is that if one decides on a single engine installation in only one hull, then a bow thruster would be a reasonable solution for close quarters maneuvering.
  11. Frosty

    Frosty Previous Member

    Its not the weight --its the torque from the thrust of one engine.

    You wanna go round in circles? Of course not so you need loads of rudder to make it go in a straight line, all this rudder causes drag.

    This gets to a point where it is more economical to run 2 engines and keep rudders straight.
  12. Boatguy30
    Joined: Dec 2011
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    Boatguy30 Senior Member

    I think this guy Evan Gatehouse with the Woods Meander has one engine. He actually wrote an article about installing the single engine, but no mention of the handling. I have sent him an email via the woods forum.

    The head will be aft in the port hull so a later second engine would need to be further aft and possibly a saildrive. There's no chance I will do a hydraulic drive.

    I have the suitable diesel engine (need to go over it a bit) and just was at a jumble and picked up a 14" by 10" martec prop which seem about right for $20.

    I suppose the thing to do is chuck it in there and see how she goes. A 1" shaft won't need to big a hole. I guess the only real decision is whether to offset the shaft, but probably best not to based on resale considerations.

    Will be about 6 months until I would fit the engine, but had an interested buyer for the engine at the moment. I'm sure I can sell it just as well in 6 months.

    Any first hand experiences still greatly appreciated.

  13. cavalier mk2
    Joined: Mar 2010
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    cavalier mk2 Senior Member

    I've moved cats with a yawl boat on one side tide up, having the power on one side works fine. Based on that and the reports of others I'd keep the shaft straight. You shouldn't need much rudder. Hydraulics have fallen out of favor though they are fairly straight forward. The deal breaker for me is the loss of power efficiency. i like the diesel electric approach, solar cells can always charge things up over time if you run out of fuel but you should be sailing anyway...... cost is an issue. I'd do as Richard suggested and use the outboard, the Yamaha high thrust is very reliable and thrifty.
  14. catsketcher
    Joined: Mar 2006
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    catsketcher Senior Member

    On my mother's twin diesel C10 we often used only one engine. It was far more fuel efficient to up the revs slightly on one than to run two. My mate does this too. You only notice any torque when starting and stopping. I seriously thought about this for my cat. A similar cat has this setup and the owner hasn't changed if after 20 years so he can't hate it that much.

    My mate with twin diesels doesn't like them. Heavy, smelly, barnacles on the props, vibrate heaps and noisy, constant drag even with folding props. A single outboard can work well on a pivoting mount. That's what I have on my 38ft cat.

    It looks as though you have a prop. I hope its folding. If you put a fixed on a multi you may as well get a mono as the thing won't sail. The price for two folding props is more than the cost of a new 4 stroke outboard. Easy choice for me.



  15. buzzman
    Joined: May 2011
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    buzzman Senior Member

    A 1975 built Crowther Spindrift 47 based at RMYC Newport NSW has a single Perkins 4-cyl, mounted on the bridgedeck abaft the rear cabin bulkhead.

    Takes a up a bit of space in the cockpit but gets the helm up nice and high..!

    However it drives two high-pressure hydraulic motors, one per hull, which take up minimal space....

    The long term owner claims exceptional fuel economy compared to cats with twin this might be an avenue worth pursuing.

    The boat is called Te Arawa, so those in the know will know who I mean and anyone curious could soon ring RMYC and leave a message....

    ...or ask for more details and I'll forward requests.
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