Stepped hulls

Discussion in 'Boat Design' started by Vibtor, May 1, 2005.

  1. xxxscimitarxxx
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    xxxscimitarxxx Junior Member

    l may be biased but the Eugene Clemence 'Dynaplane' principle is the only step hull that makes any sense to me.....standing the boat on the step and the surface piercing transom foils or plumb provides fore and aft stability as well as the greater efficiency gained from this set up....30% for any given hp of the design envelope....also the masses are balanced between these points and foreward of the step...dynaplanes dont naturally 'porpoise'......and mininal wetted surfaces between foils and step reduce surface drag.....lve only got video footage of my boat to go on for these thoughts...and admiralty tank test model data....but will be able to observe for real in the not too distant future.....new turbine soooooon.....biggest fastest dynaplane hull ever built.....100mph+....one day all step hulls will be built this way.....vorsprung durch technic.....errrrr......whatever
     
  2. xxxscimitarxxx
    Joined: Apr 2005
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    Location: england

    xxxscimitarxxx Junior Member

    l may be biased but the Eugene Clemence 'Dynaplane' principle is the only step hull that makes any sense to me.....standing the boat on the step and the surface piercing transom foils or plumb provides fore and aft stability as well as the greater efficiency gained from this set up....30% for any given hp of the design envelope....also the masses are balanced between these points and foreward of the step...dynaplanes dont naturally 'porpoise'......and mininal wetted surfaces between foils and step reduce surface drag.....lve only got video footage of my boat to go on for these thoughts...and admiralty tank test model data....but will be able to observe for real in the not too distant future.....new turbine soooooon.....biggest fastest dynaplane hull ever built.....100mph+....one day all step hulls will be built this way.....vorsprung durch technic.....errrrr......whatever
     
  3. Jimboat
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    Jimboat Senior Member

    Intrepid71 - Re: "air in mix"....

    Our research has shown that the important factor (L/D) is, in fact, reduced with introduction of air bubbles into stream. Thus, overall benefit is negative.
     
  4. yipster
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    yipster designer

  5. Doug Lord

    Doug Lord Guest

    Plum

    See post #5 this thread for more info; theres a follow up letter to the editor that's also interesting...
     
  6. cyclops
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    cyclops Senior Member

    I looked at the Hydrofoil page. I see what to me is the result of cutting a mono hull in 1/2 down the middle. Cutting the mono hull hydrofoil in 1/2 and trying to call it something new. I could go to court and convince any jury of piracy if there is a active patent for mono hull hydrofoils. Cutting something in 1/2 and getting a patent is shaky at it's very best.
     
  7. lewisboats
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    lewisboats Obsessed Member

    I've been working on and off on this concept and I would like some comments please. It is just a drawing right now, but might turn into a full blown plan. This thread on Stepped hulls has me wondering if this classifies as one of those or just a form of planning hull. I had thought to use the struts as a sort of hydrofoil/trim tab to eliminate porpoising (sp?) and to help the boat attain plane and decent trim sooner. I designed the rear to help a little with low speed operation, trying to smooth waterflow a little. Please pardon the inconsistancies between drawings, simply my lack of skill and the limitations of Paint.

    Steve
    PS: LOA 15.5', Beam 62" height 24" at max beam 26" at cockpit/seating area.
     

    Attached Files:

  8. marshmat
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    marshmat Senior Member

    From bow to about 12 feet back, that looks fairly conventional... it's what you've got in the last three feet that has me a bit confused. Are those foil-struts adjustible while underway? Also, if you're trying to plane, it looks like you'd be getting flow separation at the 'starship Enterprise' style cutaway in front of the prop. When on plane you'd then be running your prop surfaced, the foils supporting the weight at the transom (?) Effectively, once on step, the aft end of the (orange in your drawing) keel (about 3' from stern) would be the effective transom? My concerns woud be that, while climbing to plane, you'd have the stern sucked down and back by the pointy tail, and once up you'd have a turbulent air-water interface right in front of the prop and foils.
    It's an interesting concept; I'd be interested in what the pro designers on here have to say about it.
     
  9. John David
    Joined: Jul 2004
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    John David Junior Member

    This is one interesting thread even if it sometimes becomes a little sarcastic.
    When I was up to Lake Winipasauki N.H. the other week I visited the Boat Museum.They displayed some nicely restored boats that plied the lake in the 1920s and 1930s. Among them were several stepped hulls. So it's not a new idea. These steps were 2 or 3 inches high and were a little aft of midship.Since the engines back then were predominantly inboard with propellor shaft, they were located approximately midship.Probably a poor power to weight ratio to boot. The CG is clearly much more forward than modern practice which uses outboards or stern drives.I think the step was an attempt to get the planning surface more under the CG thus reducing wetted length and consequently increasing the plannig angle to one closer to optmum. I am not sure, but I think that is what happens whenever a step seems to improve speed.It is true that seaplane hulls and floats all use steps. I think for the same reason. From what I remember, the drag of these becomes much more than that expected at Froud numbers over 5 or 6, due to "spray" against the afterbody. This seems to be the problem with steps.
     
  10. cyclops
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    cyclops Senior Member

    After hearing all the replies. I think any of the answers have some real merit as to why "they" help the maximum straight ahead top speed.
     
  11. RANCHI OTTO
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    RANCHI OTTO Naval Architect

    Why to reduce stability of an high speed boat putting steps on the bottom...
    My personal thinking is that a boat has to go fast running parallel to water with a lift on l.c.b. that must be located as close as possible to l.c.b.
    The propulsive efficiency is for me more important that the resistance...
    This is possible running parallel to water surface.
    I think that steps reducing wetted surface are useful for boats with restricted range of displacement vs speed....
    My design of a 86 knots boats (Red Sugar ASD) has....not steps!
     
  12. Cary
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    Cary Junior Member

    Just go fast in rough water, you can get plenty of air under the hull. Thats why it aint worth the trouble, tooo many variables, the end of the planning surface needs a step or the surface tension will suck the water and increase drag. I prefer strakes.
     
  13. RANCHI OTTO
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    RANCHI OTTO Naval Architect

    reply to INTREPID71

    What about scale effect influencing the drop of resistance?
    :confused:
     
  14. EPClement
    Joined: Sep 2005
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    EPClement Junior Member

    Those interested in stepped planing boats will probably be interested in looking at an article about one particular type of stepped boat - the Dynaplane. That article is in the current issue (October/November 2005) of Professional BoatBuilder magazine. That issue of the magazine is available on the web site:

    www.proboat-digital.com/proboat/200510/

    Also, the design method for the Dynaplane-type of stepped boat is explained in a booklet that is available on the web site of the International Hydrofoil Society:

    www.foil.org
     

  15. cyclops
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    cyclops Senior Member

    If any body can take a scan of a books page from me I can show you that adding 6 steps to the bottom and sides of a 80' X 23' X 40 tons boat will raise the speed from 40 knots to 55.95 knots, almost 65 mph. It created a few negatives in the process. You could post the print and pictures.
     
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