Only one steerable engine on small power multihull?

Discussion in 'Boat Design' started by massandspace, Nov 16, 2018.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    A simple push-pull cable link between the two steering arms should suffice, they are only small motors, so nothing too beefy required.
     
  2. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    8 - 12 knots cruising
    An understandable dislike for extra weight and cost

    Have you considered no steering?
    I have driven similar sized ( ~28 feet ) commercial, twin-screw boats where it was easier, and more effective, to use differential thrust to maneuver through marinas ( 3 - 5 knots ) than the wheel.

    If you make two outboards steerable, your dockside maneuverability skyrockets, resale value increases, and your liability exposure drops if involved in a steering related incident.

    Redundancy? Cost?
    For harbour to harbour, coastal travel?
    Sell your two 20hp o/b's for a new, reliable single.
    Lighter, way more economical...and faster.
    Too late, I know, you're already designed and building.

    Twin the steering.
     
  3. Ilan Voyager
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    Ilan Voyager Senior Member

    I love how for a minimal saving compared to the total costs, how someone enters in a long spiral of complications and dangers. Visibly you had never driven a power catamaran of any size.
    Let's talk the experience as I have had built several for sport fishing and scuba diving and accessory water taxi.
    There is a formula that works flawlessly:
    1- Mandatory on catamarans. 2 engines widely spaced (on small ones outboards are the best solution, bigger ones Bravo 2 Mercruisers).
    2- Not mandatory but that helps a lot. Counter-rotating better supra-convergent (view from behind going forward left engine rotates counter clockwise, right engine clockwise). It's autostable by itself, even on 500 feet warships, Uboats, submarines and planes.
    3- Not strictly mandatory but when you have tried it on a catamaran it's paradise. Ackerman steering (autostable steering that helps maneuvers). That works also on 500 feet warships using 2 rudders and even better on small catamarans.
    4- Totally mandatory if you want to keep you life simple with no angers or stresses. Hydraulic steering. You have already chosen this solution. So it's simple: one "emissor" simple, one receptor cylinder, and a well sized tube linking the 2 engines. No thrills nor complications. You have 2 small engines, not 350 HP 700 pounds beasts. Probably that will be 2 outboards 50 HP 4 stroke, purring like kitties and as smooth as silk. No worries to have.

    Why this configuration?
    On a catamaran 2 engines like outboards are a huge security, maneuvering becomes a breeze as you can turn forward and almost easily backwards 360 degrees in little more that a length of boat. you can use one engine forward and the other backward and turn in place. You can park in a crowded marina the 28 feet catamaran as easily as a small European car.
    With 2 counter rotating engines and an ackerman steering you can leave the boat alone, no hands on the wheel running mid gas, it will stay a steady straight line. Very practical when you're alone and need to piss in a bucket, or open a beer. Waves in front, side, behind; no problem. The boat auto-corrects all the small perturbations.
    For general information: Hydraulic steering= minimal maintenance, no rust, no grease. Always all running smooth without hard points. You can put the steering wheel anywhere you want, even on a tower big or small. With a push pull cable doing that is a pain.
    Maintaining a push pull is sweaty, dirty and stressing. Just 2 discreet hydraulic teflon tubes you can make yourself with simple tools. These things last years and years. as all the mechanism is preserved in transmission oil...
    Connection between the 2 outboards a simple adjustable bar like on a car direction. You can make it yourself with an aluminium tube 6061 T6 anodized. No rust, No paint. No maintenance.

    Why to risk your pleasure, your boat and your life for a few bucks in false savings??? It's straight and simple.
     
    Last edited: Nov 18, 2018
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  4. fallguy
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    fallguy Senior Member

    What about heavy beam winds? Wouldn't it suck to lose the helm because one motor is going straight (which isn't really straight with the wind)? It might actually happen; especially when you'd need it most. Of course, this assumes your engines are light for the job. I'd say they are...on a good guess. One motor would have more trouble than the other based on wind direction, etc. Then you lose the helm and want to do a circle and try it again and you can't turn quickly cuz one motor is running straight.

    I hate to burst the bubble, but at a minimum, you better make sure you can run down to that motor and swing it to a starboard or port steering position for bad conditions.

    I am doing the same setup for a 32' power cat, engines 12' 6" o.c. and I am using a liquid tie bar. I would never consider the proposed option unless I was building a boat in the bush somewhere.

    The solution you propose for missing this in design or trying to save a few pennies is a bit incomplete. If you set it up so the motor can be moved for a weather helm; it might work, but it might really suck when you get close to port or realize you need it and have to put the boat in neutral to move a steering position. I think if you were going to do it; you'd at least put a couple small cables in place for adjusting without being at risk of falling in..

    Nope. On further thought, forget the idea of partial steering. It is horrible. If you do lose the helm on high winds and you have the motor turned; it could be even uglier.
     
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  5. Mr Efficiency
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    Mr Efficiency Senior Member

    What's this "liquid tie bar" business, fallguy ?
     
  6. fallguy
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    fallguy Senior Member

  7. Squidly-Diddly
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    Squidly-Diddly Senior Member

    you mean "pull-pull"? two cables so the one doing the work is in Pull mode. maybe bike style chain and sprockets, if the path not to squirrely. Same idea, side of chain doing work would be in Pull mode.
     
  8. fallguy
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    fallguy Senior Member

    A pull cable might work, but you'd need a spring or a two cable system because a cable won't push. And it would be squidly diddly on a cat if you went to the other motor. The minimum run would be from the engine and turn 90 to the aft beam with another 90 at the beam and another 90 to the other hull and still another 90 at the slave motor.

    But I feel his pain. Another cylinder and tie valve is like $1000 usd.
     
  9. Ilan Voyager
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    Ilan Voyager Senior Member

    Using cables or chains is a lot complications and a lot of further maintenance for an uncertain and unreliable result.
    Keep it simple like on a car: one hydraulic cylinder and one or two tie bars . A good system if the distance between the 2 engines is a bit big is to use an intermediate tiller placed at middle of the rear beam. The intermediate tiller receives the connections of the 2 tie bars of the engines. The tiller can be used as urgency manual system if the hydraulic fails. The geometry is pretty interesting, as it can create a useful differential when turning, like the front wheels of a car.
    Because the problem and solution are exactly the same as on a car, less the complications of the movements of the suspensions. It's foolproof, strong and simple and can be made DIY with little tooling and a bit of brain.
    It's just connecting 2 small outboards on a small 28 feet catamaran, a problem simple and straight whose solution and its variants are known since decades. Just a AB-BA first level mechanical problem in the design of a boat.
    At the prices of today I estimate at first sight the cost of a one hydraulic cylinder steering system ( for a 200 HP engine 6.5 turns) plus 2 DIY tie bars for 2 outboards 50 to 100 HP to be around 1500 bucks complete. It's just a fraction of the cost of 2 outboards with electric tilting, and a small fraction of the total cost of a 28 feet catamaran running somewhere around 20-25 knots.
    If you thinking for cheaper solutions that means you are not able to afford a 28 feet catamaran, and you have to go for a cheaper boat with 1 engine and no hydraulics like a 20-25 feet simple monohull that would be able to run at 15-18 knots.
    It's that I've done myself for my leisure boat a bunch of years ago: 25 feet monohedron, 1 engine 80 HP 3 cylinders Yamaha Enduro 2S, carefully tuned alu propeller. Simple, easily built, "dirt" cheap, comfortable, easy to maintain, largely enough for my purpose which was day exploration of the reefs and mangroves and fishing swordfish, dorado dolphin fish, sea bass, emperadors et some smaller fishes with my wife and good friends.
     
    Last edited: Nov 26, 2018
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  10. Richard Woods
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    Richard Woods Woods Designs

    As some of you know, I also have a 28ft powercat driven by twin 20hp outboards. I have now cruised over 6000 miles in it, both in the PNW and also Texas to Bahamas. You can see more here
    Sailing Catamarans - Skoota 28 transportable minimum live aboard cruiser http://sailingcatamarans.com/index.php/designs-2/6-powercats/264-skoota-28

    I use twin push pull cables, no tiller bar no problems. Extra cost over one cable is minimal. Crazy not to have both engines steerable.

    A couple of points. When manouvering I use the engine throttles/gears to turn, I don't turn the engines themselves. This video, go to 52secs in, shows a Skoota 32 turning on the spot with one engine forwards, one astern. engines kept in line. Very easy, the guy at the wheel is the boatbuilder and had never been on a boat underway before.



    Unless your boat is very light, under 1T empty, 1,3T say loaded, you won't do 8-9knots as a cruising speed whatever size engine you use. You will do up to 7 knots on one engine, or over 10 on two. the 8-10 is the "hump speed" for want of a better name. Inefficient for any distance

    Richard Woods of Woods Designs
    www.sailingcatamarans.com
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    This has confused me, are you saying the OP's 28' cat won't be able to run efficiently at 8-9 knots ? I assume he has a displacement cat in mind.
     
  12. fallguy
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    fallguy Senior Member

    It should be noted, I am using hydraulic steering to simplify demounting the cat. My cat can come apart for legal trailering, but has a 16' 6" beam. With quick disconnects, I will be able to move steering lines back into the hulls for land transport.

    If I wanted to save the money, I would avoid hydraulic steering.

    As Richard points out, you can also steer a cat with throttles, but I don't think he means to suggest skipping at least p/p cables.
     
  13. Richard Woods
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    Richard Woods Woods Designs

    yes that's right, assuming it isn't a lightweight boat (I don't know anything about the design). "Efficient" might mean running at half throttle, maybe 3/4. Show me a F27 or a Stiletto, essentially the same length, that can do 9 knots under power with a small outboard. And those are light boats

    RW
     
  14. fallguy
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    fallguy Senior Member

    Fancy that. Two steering wheels.
     

  15. SamSam
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    SamSam Senior Member

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