Stepped hulls

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

  1. cyclops
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    cyclops Senior Member

    How many happy people do you get at the completion of a house compared to a boat completion?
     
  2. wdnboatbuilder
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    wdnboatbuilder Senior Member

    It seems that nobody is happy in the home building bus. Ralph Stanley told me once " if build a boat ,people will come." and I have just never put that wisdom in effect. Maybe I should. And I will have to say he has not been the only one (Master Builder) that has told me those same words. In the last 3 years I have really been rolling it around in my head. Maybe one day I will get the guts. Anyway I thought we were talking about stepped hulls. Let me ask, how does a step work out on a warped bottom?
     
  3. cyclops
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    cyclops Senior Member

    Should give similar friction reduction at +40 mph. It is simply the act of reducing the area where solid water is being forceably dragged across the solid hull bottom. Reduce the solid areas any way you can. ----- The rest of this is not relative.--------------------------------------------------------------------------------------------------------That is why a TRUE constant deep V hull of about 28 degrees is so wastefull of HP and speed in calm water conditions. If you take and spread the 2 bottom 1/2's of a same beamed boat flat . The warped bottom area is much less.-------------------------------------- But in a storm sea condition, 28 degrees will come out and rescue any other type of hull in trouble. Hull design can be simply, speed or safety? All other features are distractions when you in a hurry to get there, or hoping you will not die in your boat on the way back to safety. --------------------Next speaker.
     
  4. 951kid
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    951kid New Member

    Just a thought, this is a long post so im not going to go back to quote someone, but as this person suggested the importance of the step is to take advantage of the higher pressures of water after the transom, which in the case of a stepped hull is used by the aft section of the hull.

    if there was no pressure difference between either section of a simple single step hull then i would need to beilve that the wetted surface would be the same as a similar hull without the step.

    my logic might be too simple but... the amount of area for the pressure of water to work on would need to be the same on either a steped hull or standard hull in order to produce the same amount of lift to get the boat onto a plane, that is if the pressures were different due to the step.

    so im suggesting maybe reserch needs to be done on finding the area of greatest pressure to the stern of the fore section of hull in order to have the aft section of hull take advantage of this
     
  5. Jimboat
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    Jimboat Senior Member

    Stepped hull design

    951kid - well, you're on the right track, but maybe not for the engineering reasons that are generally accepted. Stepped bottoms have 2 major advantages over non-stepped hulls... 1) they can maintain near optimum angle of attack throughout a wider speed range, and 2) they can reduce the amount of wetted surface that is not near the leading edge (and is therefore not producing as efficient lift). A properly designed stepped hull will indeed produce "more efficient" lift, so the wettted surface required will be somewhat less than a non-stepped design - thus less drag. But there are also many issues to deal with, in designing stepped hulls that will be truly effective throughout an entire hull speed range.

    Check out the post on stepped hull design at another site, as it discusses similar issues to those you are addressing.
     
  6. tom28571
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    tom28571 Senior Member

    Jimboat,

    Your 1st point about maintaining an optimum angle of incidence is one that is often overlooked in the speed advantages of a stepped hull. It also answers kid's question of why wetted surface can be lower in a stepped hull at the same speed and load. Increase in bottom loading/area is more than offset by reduction in skin friction.

    Jim, I just read your post on the link. Great discussion. We accept that the lift on the bottom decreases toward aft. What are your thoughts on the reason? My thoughts are based on Newton's reaction laws.
     
  7. EPClement
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    EPClement Junior Member

    In his message #64 on the subject of stepped boats, 951kid has passed along a suggestion (made by someone else) that there are “higher pressures of water after the transom…” That is an entirely erroneous idea.
    His message #64 also very reasonably suggests that, “…maybe research needs to be done on finding the area of greatest pressure …” Fortunately, comprehensive research of that kind was done (many years ago) in the Seaplane Towing Tank of NACA (the predecessor of NASA). Thorough pressure measurements were made on planing models having different deadrise angles at ranges of speeds, loads, and trims. Those tests showed that the maximum pressures on a planing hull are near the forward boundary of the wetted region. The pressures decrease rapidly aft of that forward boundary and are very low on the after part of the bottom of a planing hull. Accordingly the after part of the hull bottom of a conventional planing boat contributes very little to the lift but contributes greatly to the frictional resistance of the boat. If an appropriately designed step is introduced the drag can be substantially decreased. Drawings given on my web site (www.dynaplaneboat.com) show what can be achieved. These show a comparison of the wetted areas for a conventional planing boat and an efficient stepped boat. The stepped boat has less than one third as much bottom wetted area as the conventional boat and therefore has less than one third as much frictional resistance. The stepped boat shown incorporates a device for controlling the running trim angle. The very comprehensive dissertation on stepped boats given in the link that Jimboat provides in message #65 explains the difficulties that are likely to be encountered by a stepped boat that does not have the benefit of a means of trim-control.
     
  8. Jimboat
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    Jimboat Senior Member

    EPClement - It's great to see your responses in these threads. Mr. Clement eloquently explains why a step has the potential to improve planing perforamnce...since "maximum pressures on a planing hull are near the forward boundary of the wetted region"...and "...pressures decrease rapidly aft of that forward boundary...and the after part of the bottom of a planing hull". This occurance, is a major contributor to the potential advantage of stepped hull design. The step allows the wetted surface to take advantage of the "most efficient" zone of hydrodynamic lift. The design trick is to design a stepped hull design that will do this, with stabilty, throughout the operating velocity range! Research that we have done (at AeroMarine Research) and in colaboration with Morley Smith, confirms these planing pressure zones.

    (Note: I hope all reading this thread recognize how fortunate we are to have the comments from EPClement - Mr. Clement is one of the leading authorities on planing hull research and design - I have learned much from his works. Thankyou Eugene, for your presence here!)

    p.s. - Mr. Clement published an excellent article in Oct/Nov 2005 issue of Professional Boatbuilder on Stepped Hull Design - worth the read of all interested in this thread!
     
  9. Doug Lord

    Doug Lord Guest

    Thanks, Mr. Clement

    I want to second what Jimboat said! And while my interest lies in the exploration of the use of steps (esp Plum type and Clement types) in sailboat design I read everythng Mr. Clement writes and I sure appreciate his comments here. Thanks again, Mr. Clement!
     
  10. cyclops
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    cyclops Senior Member

    How does a stepped hull 19' bowrider with a FULL USCG load of people perform empty and full? Time to plane--- full speed--- turning and maintaining planing speed compared to a Searay stern drive.
     
  11. yipster
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    yipster designer

    ten years? back i recall reading searay designers thought their R&D on V hulls was so optimized they were not going to devellope stepped hulls.
    but how is that today? the easy question may not be so straightforward to answer, but yeah:
     
  12. chase687
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    chase687 Junior Member

    Mr. Clement

    After reading the dynaplaneboat site I was left wondering how sensitive to loading would a boat of this design be compared to a conventional hull design without steps. Also how important is the hull shape after the step to performance and ride quality? It seemed like in the picture that the portion of the hull after the step was out of the water until the aft foil? And since I am asking questions, what affect does wave action have on the lift created and because of that what is the tendency of motion of the hull and is that motion better or worse for ride quality compared to a conventional hull without steps?

    Sorry for the poor wording of the questions. I am not quite sure how to ask what I want to know.
     
  13. EPClement
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    EPClement Junior Member

    Cyclops can determine the answers to some of the questions that he asks in his message #70 by means of the calculation procedures that are given in my booklet about the Dynaplane design (available on the web site of the International Hydrofoil Society: www.foils.org). Others could only be answered by the trials of an actual boat.
    The booklet provides the information needed for designing the hull forms, cambered planing surfaces, and stabilizers, for Dynaplane-type boats of a wide range of sizes, weights, and speeds. However, the design procedure is still admittedly incomplete. The propulsion arrangement I propose is by a right-angle drive coming out through the bottom of the afterbody - as shown on my web site (www.dynaplaneboat.com). At the present stage this is schematic only and the details have not been designed. I am depending on the appearance in the future of someone younger and more energetic than I now am who will complete the design and advocate its adoption. I believe that the eventual result will be the introduction of a markedly improved motorboat design that will use less fuel, cause less pollution, and be more fun to operate. A final word to the planing boat designer is that designing a boat with a cambered planing surface and trim control is much more fun than designing the other types of planing boats. The reason for this is that the designer can have the satisfaction of “zeroing-in.” with his calculations on achieving optimum performance. This is not possible when designing the other types of planing boats.
     
  14. trouty

    trouty Guest

    Interesting site Mr Clemments

    I always like to look at something different. I enjoyed your web site on the dyna plane boats.

    I can't help wondering about the Hysucat foil assistaed craft, and whether a dynaplane or hysucat foil are a better solution?

    It appears as tho a lot of the large fast ferry Cat builders are going with Foil assisted cats for stability reasons one would presume.

    Is there a reason we don't see more of dynaplane / stepped hull - in the fast ferry type indutry, compared to the foil assisted cats?

    Just me thinking (wondering) out loud!

    Thats what I like about this web site - I often go away - thinking.

    (In case you havent realised - thats the whirring / clicking noise you sometimes hear!):D

    Only the other day someone said to me (an idea I've been thinking about for a couple years now) that they are designing a planing tri hull (English vortex hull) - with two foils - one between each wing and the centre hull...
    (Actually it was the naval architect who designed the sea Gyro stabiliser I posted about a few days back - very clever fella!).

    Why hasn't that been done before? (Aany good reasons anyone can think of?)

    Cheers!
     

  15. cyclops
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    cyclops Senior Member

    It should be cost per mile. The less boat in the water, the less maint. And more eff. They run at all % of loads and speeds.I think a check of, HP/ton/mph reveals they are top dogs right now. Cost per mile RULES in business.-------Mph is really time on ferries.
     
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