stepped hulls and other planing devices

Discussion in 'Boat Design' started by kerosene, May 20, 2009.

  1. kerosene
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    kerosene Senior Member

    Reading Uffa Fox's Seaman Like Sense in Powercraft (was:Gerr's nature of boats) the speed record boat with hydroplaning hull with several steps always haunts me. I t is presented as such a great boat but you cannot see any modern boats with multiple steps.

    It would seem that you could have the good sides of the narrower boat yet wide short planing surfaces. Is there some specific reasons why ths is not sensible.

    Also - I am always dreaming of boat that could have the benefits of displacement hull - efficiency at slow speeds - less slamming etc. yet be able to plane when needed.

    Attached is a clumsy presentation of something that was on my mind. I guess it starts to go into the hydrofoil category. Anyway the idea is that the hull itself narrows to the stern so it has less water to drag behind it. The side wings add to the wetted surface but not so much to wave making. Once speed picks up the broader flat area helps in planing.

    I am sure it would be done already if it was a ticket to heaven - I'd liek to know why its a bad idea.

    edit: had the books mixed up - too tired at these hours... Finishing a project on Wed.
     

    Attached Files:

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  2. mydauphin
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    mydauphin Senior Member

    Kerosene, a smart question. Congrats. I don't have a lot of time now. Will be back later to this but suffice. There are many threads here on steps particularly multi-steps. Multi-steps are a great idea, but even single steps are complicated and beyond most mortal calculation and even most computer models. Multi-step is more of trial and error in real world, that said, I believe main problem with these is boat owners. You design a boat one way and owner fills it up with junk and change weight distribution totally. It seems step hulls are more sensitive to trim changes. On your fin idea. Only way to really tell is build test model, my guess it would provide to much lift in transom. And depending on boat that may not be where you need lift. Later
     
  3. kerosene
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    kerosene Senior Member

  4. gonzo
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    gonzo Senior Member

    As you described it: a narrow hull with steps, makes for a hard sale. Marinas charge by the linear foot and owners want interior space. There are several companies, like Regal, Monterey and Sea Ray making stepped hulls. However they have one or two only. The increase in performance is quite good. The down side is that they come off a plane much faster and harder.
     
  5. tom28571
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    tom28571 Senior Member

    There are many multi-step hulls on the market. The main reason you don't see a lot of them is that they are a one trick pony. Unless they are up on step and moving fast, they are not very good boats in any sense. As gonzo said, there are other downsides. Step boats have extremely high longitudinal stability. Not a problem in smooth water but make for very hard riding in rough water. I remember a boat from the 1960s' that had dozens of small steps but never made it to the market. Just up the road a ways, Reggie Fountain makes a lot of step boats. None are very useful for other than racing or macho symbols.

    As for the aft wings, Calkin's Bartender usually has them and Latin American pangas also have them. They are used to correct a deficiency in the shape of pointy sterns. Unless you just have to have a pointy stern, they don't serve any purpose. Take a look at the double ender thread.
     
  6. HJS
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    HJS Member

    Check midship interceptor and aft stabilizer on the outboard engine.
    It works if done the right way.
    Patent pending.

    JS

    www.sassdesign.net
     

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  7. kerosene
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    kerosene Senior Member

    HJS, Oh I saw that earlier - and I think its is extremely genius application of simple "common sense" device.

    It is exactly along the lines I am after - practical solution for something that is not super speedboat but small lake, calm sea everyday boat. Improvement on efficiency more so than extreme speed.
    I am from Finland myself and plan to end up back there eventually so lakes and Baltic are going to be my water ways.

    Any new videos? Best of luck with the project.
     
  8. eponodyne
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    eponodyne Senior Member

    What you've drawn looks very much like the "dynaplane" concept. This is a system whereby the forward part of the hull, just for'rd of the step, is shaped like a wing. The planing area is carefully calculated and shaped to provide minimal wetted area at plane. The forward hull carries most of the load (the engines are located forward of the step, for example) and the aft hull is supported by a surface-piercing V-foil.

    What you have come up with, all on your own, is an echo of this concept. I like the idea of your aft fins kind of built in very much. I think this is an idea that might bear fruit, and I hope you move on to model-making and testing. I'm very interested in stepped, narrow planing hulls myself, so feel free to drop me a PM and we can discuss this in our own time.

    Epo
     
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  9. gonzo
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    gonzo Senior Member

    The plate on the motor is a slight variaton of the doelphin and many other types. If it really worked the engine manufacturers would install it. They are interested in performance and have tested all those magical inventions. As for the "small lifting surface", what happens when the boat pitches and rolls? Those designs have one thing in common: unless the water is completely flat and the boat in perfect trim, it drops and pounds hard. It oftend leads to loss of control.
     
  10. HJS
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    HJS Member

    stepped hulls

    gonzo

    Are you referring to personal experience of stepped hulls like the dynaplane or the midship interceptor concept or an other type of stepped hulls? Which?

    The plate on the motor is not a small doelphin. We tested them, they did not work in this application.


    js
     
  11. gonzo
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    gonzo Senior Member

    I have personal experience with a variety of production and some custom stepped hulls. I don not say they are bad, but that they have a different behavior than traditional hulls. In my opinion it takes more attention and experience to handle them. Also, I didn't say it was a small doelphin but a variation of it.
     
  12. gonzo
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    gonzo Senior Member

    Kerosene: those lifting surfaces are known as hobbles. They were installed in many converted sailing workboats to prevent them from squatting and increased speed
     
  13. TollyWally
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    TollyWally Senior Member

    I've always been fascinated with the stepped hulls used as small plane pontoons. I've looked at the pontoons many times on bush planes up north.

    The pontoon is a classic single stepped hydroplane hull with some unique properties. The weight of the plane at rest bears upon a deeply rockered "displacement" hull. Aft of the step which appears to be aft of the bulk of the weight of the plane the dead straight planing surfaces are cocked up around 15 degrees or so. When taxiing it is all about the rockered hulls but when the power is applied the plane rocks back onto those flats, the prop starts pulling for the sky and the craft builds speed quickly.

    Perhaps a bit off topic but I think of those stepped pontoons often always wondering...
     
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  14. Yellowjacket
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    Yellowjacket Senior Member

    One thing about airplane floats is that they aren't really designed to be much of a boat. They are there for takeoff and landing primarily, so the ability to get up on a plane and not have a lot of drag in either the boat or flying mode is what the designer wants. There is very little consideration of handling properties that are necessary for a boat, since at low speed these are displacement hulls.

    In a stepped boat hull, the step serves to help control the angle of incidence of the aft part of the hull that is also in the water. In a float plane the aft part of the float is there to act like a displacement hull and keep the tail out of the water when the hull is at rest and at low speed. In that sense it acts more like a dynaplane than a conventional stepped hull.

    Since an airplane needs about 10-12 degrees of angle of attack to generate sufficient wing lift to fly, without a step you would have to angle the hulls at about 10 or 12 degrees nose down to allow the airpane to fly, and that would add a lot of drag (and even worse, a lot of downforce) when you are flying.

    Essentially, once a float gets up on a plane, it acts like conventional planing hull that stops at the step, not like a stepped hull as we generally look at one. The step is only there to allow the planing section to attain higher and higher angles of incidence and therefore to continue to create lift as the speed increases and the nose pitches up to take off. The first attempts at seaplanes found that they couldn't lift off the water since the suction of the aft surface (area that was necessary to keep the tail from dropping into the water) actually kept the hull stuck to the surface. While the CG is forward of the step you still need a lot of volume behind that point to keep the whole shebang from tipping nose up, but that is all the aft part of the float does.

    Aircraft float designers hate the step since it adds a lot of drag in flight, but it is considered a necessary evil that they live with because they have to.
     

  15. TollyWally
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    TollyWally Senior Member

    Thanks for the scoop Yellowjacket. I've spent countless hours looking at those pontoons, dry,wet,taking off and landing.
     
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