Tunnel Rudders, Twin Rudders and similar.

Discussion in 'Propulsion' started by tom kane, Aug 30, 2013.

  1. tom kane
    Joined: Nov 2003
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    Location: Hamilton.New Zealand.

    tom kane Senior Member

    Has any one had success using tunnel rudders or twin rudders and getting good steering results? Most of the ones I have tried or seen do not cut the mustard and impress me but all seem to interfere with the water flow to the prop when used to turn and especially on a sharp turn.
    Some even require you to slow down to make a sharp turn. Not many problems going slow and maneuvering if the rudders are of the spade type and deep below the prop but still trouble turning going at speed.
     
  2. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    I use twin rudders adjacent to the prop. The steering is "logarithmic", small rudder angles do almost nothing, only when the steering angle is large enough for the rudder tip to reach the prop wash there is reasonable steering effect.
    There are 2 engines, so instead of steering I usually play with engine rpm and fwd/reverse to put the bow in the proper direction.
     
  3. tom kane
    Joined: Nov 2003
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    Location: Hamilton.New Zealand.

    tom kane Senior Member

    As I said I have experimented with every design of flat plate and foil, tunnel, Kort nozzle shape rudders and found long deep spade rudders the only ones that give reasonable steering up to about 10 degrees max each way from center. Like the ones used on high speed surface propulsion. But the faster you go the less steering you can use.
    Because I wanted shallow water performance I could not use long deep rudders with surface propulsion. I even tried a long spade rudder that slid up and down and that was good. The theory of foil performance limits any rudder to to a maximum of 20 degrees steering over all if you are lucky. a trim tab may increase this by an extra 5 degrees.
    I used twin rudders each side of the prop and back from the prop as far as possible,about 6 inches for shallow water work. These rudders overlapped each other when full turned left or right and gave good maneuvering going slow and even a degree of reverse. the boat could turn in it`s own length.
    Can anyone come up with a rudder that can compete with the steering of an outboard,but not a sailboat.
    www.rudderpower.com is interesting
     

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  4. myark
    Joined: Oct 2012
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    Location: Thailand

    myark Senior Member

    Hi Tom
    After meeting you on the Waikato river those many years ago discussing your pivotal drive system I have since had planes to make small runabout like you did in 1960ish with the small ford prefect motor in a 14’6”Hartly I think.
    Life is short with so many things to create; times caught up on me especially the amount of finance needed to bring ideas to fruit.
    When I succeed I will make your pivotal drive system fit into a Myark cat design at no cost.
    This design cat has a special design to suit your pivotal drive systems that allows a larger motor.
    Terry Rycroft also a friend in NZ and the inventor of the aqua amphibious Gibbs car said to me he did not worry if it makes money, he wants to see the idea work which was enough reward.
    I will want the same.
    One of the largest hand tool companies in the world has invited me to develop my wrench ideas further in a joint venture and if so I should have finance needed and if that happens let’s do it.

    Pictures are myself holding my son Myark also the spooky picture of the work shop Mercer I stayed in where we met and you parked your car while river boating.
     

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  5. JSL
    Joined: Nov 2012
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    Location: Delta BC

    JSL Senior Member

    On a slow full tunnel boat I used a tube type rudder & it worked well (much like a water-jet). On a fast(er) boat (20 kn+) a rudder will 'choke' the water flow like a flap valve so we fit the rudder on the transom and/or flare the tunnel.
     
  6. tom kane
    Joined: Nov 2003
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    Location: Hamilton.New Zealand.

    tom kane Senior Member

    Interesting comments JSL shows everybody is looking for something with more control than a standard rudder.
     
  7. tom kane
    Joined: Nov 2003
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    Location: Hamilton.New Zealand.

    tom kane Senior Member

    Tunnel Rudders, Twin Rudders and similar

    Hi myark, There is no shortage of ideas to make boating a pleasure and safer. My greatest pleasure was having a Safe Remote fuel System to keep all the volatile fuel vapors and other nastiest from inside of my boat.It was great not having to even think about such things. There are so many ways of building a pivoting drive shaft,the trick is to build a standard production model that fits most boats.
    www.youtube.com/channel/UCWplIXLumATHxb-OLEMjmolg

    More info added with image.
     

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  8. rayman
    Joined: Sep 2009
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    Location: brisbane

    rayman Senior Member

    Hiya Tom, there used to be a boatbuilder in Hamilton by the name of Clarke who used a type of kort nozzle in a shallow tunnel for steering. His boats were about 16ft and sold under the name "Clarkecraft", generally with Ford 10 engines. His shed was out Tamahere way.
    I wouldn't go messing with that taniwha, thats in the old Mercer Rowing Club house, that shed was all constructed with volunteer labour, I may have made some of the blocks in the wall you see. We made about 3,000 blocks, and supplied those used to reconstruct the old butcher shop, Mercer Cheese last time I was there.
    Have a look at "Becker Rudders" they bend the way you want. The tunnel stern boats down on the Whanganui used twin blades, one either side of the tunnel.
    regards Ray
     
  9. tom kane
    Joined: Nov 2003
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    Location: Hamilton.New Zealand.

    tom kane Senior Member

    Hi rayman, Now that is interesting. You must know Mercer well and probably the eel fishermen on Waikato. Colin and others. No it is far to expensive playing with Taniwha.
    I Attended a Keel pouring out at Tamahere quite some time back at a boat builder there
    Ray Fink.
    I have posted some photos on this site of the Wanganui paddle boat showing the prop.rudders and tunnel. I have tried Kort and most rudder designs but found my own design of dipping rudders the best as the are only in the water when you need to turn or stop and have no drag when not in use. Lots of ways to build them though and still undecided which is best. They can become complicated. There must be more designs I have not seen.
     
  10. myark
    Joined: Oct 2012
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    Location: Thailand

    myark Senior Member

    Hi Tom

    Sorry about the long delay.

    I will explain later, going bush for a while and distanced myself from computer.

    I see I have stalkers with the minus -6 rep on boat design, can feel sorry for them.

    Cheers
     
  11. myark
    Joined: Oct 2012
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    Location: Thailand

    myark Senior Member


    Hi Tom
    With the steering I have designed a Myark cat that allows twin rudders in the front with a pivotal motion, the same as the pivotal drive system.
    This allows for the water craft to beach itself without damaging rudders that will give a direct steering allowing to 360 at high speeds.
    Its low cost way of steering that allows your pivotal drive cam to maintain its simplicity
     
  12. tom kane
    Joined: Nov 2003
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    Location: Hamilton.New Zealand.

    tom kane Senior Member

    That steering sounds interesting myark, and I think that type of proposal would work great. I have tried so many variations to steer a boat and something like a snowmobile steering worked good however it would be necessary to build a hull to incorporate such designs and when you change from a traditional hull design boaties become rather upset and can not understand the need for design change.

    I would like to see a sketch or design.I think it would still be necessary to have some form of protection around a propeller ( one season I used twin rudders) these days to ally fears people have about exposed propellers and myself am prepared to forgo speed for that protection. It is time boats were designed and built for safe and comfy travel and forget about traditional curves and appearances. I prefer things that work well not trying to impress the neighbors. I have given up on tunnel rudders,perhaps I have missed so design factors but all that type come with disadvantages and no improvement steering or maneuvering.
     
  13. myark
    Joined: Oct 2012
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    Location: Thailand

    myark Senior Member

    Hi Tom
    Your design is made to be low cost that can turn weed into power like the Gator out boards so to be able to solve the steering such as come up with a simple design like a pogo stick rudder in front that needs to reach below the water line as the front of boat rises and allow rudder to skid upwards when driven in shallow water or beached.
    I liked one of your ideas that on each side of the back of your boat you had like in the early cars that had blinkers pop out the sides that could skid the rare boat from left to right.
    I remember a light sailing cat that was in the 1980,s was steered from the front and could reach 60mph or faster and turned on a dime.
     

  14. tom kane
    Joined: Nov 2003
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    Location: Hamilton.New Zealand.

    tom kane Senior Member

    When we were kids we used to steer our sledges down hill by using our heels on the left or right side and it did not make much deference to the speed. Experimenting with boats gave good steering and there was only drag when the dipping rudders were in use in the water and any drag made turning safer.
    You can make some pretty expensive pivotal drives with exotic plastics and new steel materials and incorporate auto lifting and other fancy devices but the basic model does that anyway.
     
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