Stepped Planing Hulls/small sailboats

Discussion in 'Sailboats' started by Doug Lord, Apr 9, 2005.

  1. Chris Ostlind

    Chris Ostlind Previous Member

    Watch any of the vids on Youtube and it will all be clear. Even the pros never have the boat sailing with a side to side unwavering mast for an entire event. It just doesn't happen.

    You're an engineer, Terry, bring me a set of data that was taken off a boat that had no healing movement throughout an extended sailing session, such as one might find in a single race.

    Since you worked in a world where precision counts for a hell of a lot, I wonder if you ever tried to describe a specific, technical event to colleagues and used the suffix -ish, or a tagged-on, "more-or-less", on the end of the key defining word? Something like, "It was 240 volts-ish" but we never got it dialed in." OR "the input was 240 volts, more or less, and it gave us fits". Oh, really, how much more... or less, was it exactly?

    Since our friend is a stickler for proper definitions and is totally immersed in numerical data as a means to describe the performance of a boat, one can only wonder as to what parameters are allowable under the term "flat". Flat exists in a wind tunnel when the model hull is rigidly fixtured to the building. It’s not a truth in the world of sailing.

    So, I'm holding his description of "flat" to the same level of precision that he has used when badgering the Foiling Moth World Champion, as well as many other posting members.
  2. ancient kayaker
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    ancient kayaker aka Terry Haines

    Ah! Chris, I see where you are coming from - "flat" as in "riding on rails"

    In that case flatish would be more correct.

    Our use of the word "flat" was only correctish :)
  3. Doug Lord
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    Doug Lord Flight Ready

    flatish, no heelish

    Isht sorta sillish...
  4. Chris Ostlind

    Chris Ostlind Previous Member

    Was that supposed to be silly-ish, or what? Couldn't quite tell.

    Make yourself accountable for your own pedantic, wordsmithing behavior as a start and we can talk about making this conversational, rather than a lesson in grammar and definition.

    Face it, Doug, you're a poor writer and an even poorer example of a guy who should be chasing a World Champion in the one thing you claim as your field of expertise. Just think of what you could learn from the guy if you only presented yourself, sincerely, with hat in hand and apologized for past transgressions?

    Bora knows stuff about foiling, inherently, about which you can only guess. To let such a rich resource fall out of your grasp is near criminal for the Mr. Foil, Doug Lord.

    After smooching Veal's butt for years, you should already know this.
  5. C 249
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    C 249 Junior Member

    I may be getting my wires crossed since I don't have my archives to hand, but I think it was done in 1977 with the Aussie Vee Jay classer (12' high performance dinghy) Nu Hissy, among many other attempts.

    If I recall correctly, Nu Hissy - sailed by the designer of the current 16 Foot Skiff - won the nationals but the stepped hull was not seen to be the reason.

    It has also been used on boards, a Ross 930 owned by Graham E on Lake Macquarie in Australia, and other craft.

    At no time has the concept showed all-round speed worth pursuing.

    In many ways, it's not hard to design a hull that's faster when planing fast. Any decent designer probably knows how to do that, in almost any class.

    What is hard is to design a hull that is fast enough when planing, and controllable at all times, and faster when not planing.
  6. Doug Lord
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    Doug Lord Flight Ready

    Stepped hulls/ Midship Interceptor

    Thanks CT. What I find interesting is the potential with Eugene Clements and Jurgen Sass developments for increases in speed of 25 to 50% with the same power.
    Clements is unique among stepped designs in that his system uses one very small step coupled with an adjustable rear surface piercing foil, Jurgens Midship Interceptor uses a retractable(and adjustable) plate that extends down slightly and a rear foil. Jurgen feels his system is adaptable to planing sailboats and so do I. Clements system is more complex but may also be adapatable.
    Seems like ,with the potential gains that are possible, some experimentation is in order.
    Do you have any details of the boats you referenced?
  7. Doug Lord
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    Doug Lord Flight Ready


    Have had continued conversation with Eugene Clement in regard to a planing hull sailboat benefiting from the dynaplane concept-proven in extensive testing on powerboats. Mr. Clement sent me his 60+ page booklet that contains a great deal of information on this system.
    1) The first hurdle was whether or not the boat would be sailed heeled like many sailboats or flat like most planing hull dinghies. Flat,for sure..
    2) Second hurdle was with its given displacement(474-550lb) what would the Volume Froude Number be. Mr. Clement said that it had to be above 3.0 to be a candidate for the system. Using the nomograph provided in his booklet I was able to determine that for 15 knots boat speed the VFn=3.3 and for 20knots the VFn=4.4 .
    3) The system is not ideal in rough water conditions but that really is not a concern since even w/o this system planing performance should be at least as good as a normal hull with foil assist.
    4) Mr. Clements system uses a surface piercing foil at the stern to hold the surface of the hull aft of the step clear of the water. Running attitude is adjusted by moving the whole foil up and down. That won't work on the planing hull sailboat design I envision because of the rig and the method of achieving righting moment. The boat will need lift upwind at the transom(or at least can use it) and will need downforce at the transom going downwind. Two solutions have come to mind so far: 1)- use a symetrical foil on the rudder with a wand system connected to the foil flap. The wand would take care of up or downforce as needed. Raise and lower the whole rudder/foil assembly to change running attitude for different conditions; or,2) Use a direct manual link to the flap on the foil to control attitude. This is a simpler setup but would possibly be labor intensive under sail.
    Both would require a speedometer to help get the settings right- at least initially. There may be other solutions not yet considered.
    This all seems very encouraging...
  8. Doug Lord
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    Doug Lord Flight Ready


    More has been learned about implementing a Clement -type small swept-back step on a 17' planing hull with a chine beam of 3.2':
    1) step height would be only .38" (1% of beam at chine)
    2) the Clement system uses a cambered section developed by Virgil Johnson.
    a-flat plate L/D= 11.5
    b- Johnsons cambered section L/D= 17.5
    c- actual tested L/D on Clements swept back step exceeded these
    d- the swept back, cambered planing section is located close to the
    CG of the boat.
    3) hull drag for a planing hull using Clements system does not increase with increase in speed.
    a- appendage drag and air drag does increase.
    4) potential speed increase of a correctly implemented dynaplane system over a "normal" planing hull is approximately 50%.
    I want to thank Eugene Clement for his help and encouragement in developing
    the application of the dynaplane concept to a planing sailboat.
    Illustrations from proboat article by Eugene Clement:

    Attached Files:

  9. bistros

    bistros Previous Member


    Are you planning to develop the Dynaplane concept for a planing sailboat?

    Last time I looked, you were building a single Cat-hulled foiler/technology testbed platform which would incorporate buoyancy pods, the Trapwing idea, your sliding bench seating and a host of other concepts. I've got some uncertainty about the size of your project - sometimes it seems like 16-18' and others it seems like 21' - I'm just not sure and haven't paid enough attention I guess. Maybe you are building more than one boat at a time.

    All of your discussion to date seems to centered on foiling for this build, not planing. Are you going to build a planing monohull as well? Perhaps a new planing RC boat as a technology testbed? I seem to remember you talking about stepped planing amas as aeroSKIFF rev 2.127 buoyancy pods at some point, so maybe that's what you are investigating this for.

    I'd sure be interested in seeing some solid research data and conclusions regarding the Dynaplane concept across a wide variety of conditions and speeds.

    Thanks for continuing your ongoing Quest for the Holy Grail of performance sailing by turning over all these stones which hide ideas missed/rejected by the mainstream folks.

    You are to foiling what Steven Colbert is to conservative punditry and values.



    I did have an idea for your sliding bench seating - put a rotating "Lazy Susan" type of cushion on the bench, so tacking or gybing could be an exercise of "Spin, Kick & Slide", ending up facing the right way on the other tack. That way you won't have to lift off the bench! I'll assign the patent rights for "Spin, Kick and Slide" to you if you wish! You could get Vince from the Slap Chop (w/ Graty!) to be your pitchman!
  10. Chris Ostlind

    Chris Ostlind Previous Member

    "You're gonna love my nuts!!!"

    But wait, there's more.
  11. MalSmith
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    MalSmith Boat designing looney

    Chris, I sailed Vee jays around that time (1976), but I don't recall that Nu Hissy had a stepped hull, unless steps were added later? I forget the name of the guy who sailed it, but he was a legend in the day. I do recall that another Vee Jay at that time had four aeration slots cut into the underside of the hull. That didn't seem to make any difference either.
  12. Doug Lord
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    Doug Lord Flight Ready

    One thing for sure-a stepped hull won't work unless it is designed very carefully and based on well researched data. The proboat article by Clement (posted earlier in the thread) documents some of his research and his 60 page booklet detailing the requirements for the design of the dynaplane concept is available for the asking.
    The fact that the Clement step is so small is a big plus in considering it as is the fact the the step gets smaller closer to the chine. The boat can be heeled and pitched bow down for light air and it appears that the step and cambered planing area would then have negligible drag. At this point, I don't think any variable geometry solution would be required to use this idea effectively.
    It also appears that the entire planing area may be able to be molded and placed on a suitable hull in such a way that it could be moved fore and aft for testing purposes.
  13. daiquiri
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    daiquiri Engineering and Design

    Doug, I've just recalled that there was an ocean racer sailboat back in the 90's, Her name was Route 66. It featured a small aerated step in the mid-hull which (so I've read) worked well. Just for your info, if you have time to search around for more... ;)

    P.S. - Update:
    I have made a search in one of my old folders and have found these two files which talk about Route 66. They are not too technical, but may help in finding the right persons to contact for more info. Uploading them here.

    Attached Files:

    Last edited: Jan 15, 2010
  14. Doug Lord
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    Doug Lord Flight Ready

    Slavi, here is Erics response to my e-mail-(posted with permission):

    "Yes, I put an air lubrication system on Project Amazon. My client and I hired Lars Bergstrom for design advice, actually. I also hired Steve Pettengill, the skipper of Hunter's Child in the 1994 Around Alone Race, for design advice and experience. Lars had worked HC's air system out too. The principle seems to work, but you have to put the air vents in the correct fore/aft location. In HC's case, because of the round bottom, she had to have her deflector plate ahead of the air vents in the permanently open position. On Project Amazon, because of her flat bottom, we had opening/closing vents that you could open at will. The owner ultimately simply drilled holes through the bottom, with no deflector plate, and at high enough speed, you could hear and feel the air rushing through the bottom of the boat. Both my client and Steve Pettengill seemed to think that the air system helped to keep the boat on plane a little longer than usual, but it did not help the boat to get up on plane. Personally, I think the differences in speed were minimal, and in the overall scheme of things, they probably are not that effective, even though the principle seems to work."

    Clements dynaplane concept also requires a source of air just aft of the step at the CL of the boat.....
    Slavi and Eric-thanks for the information-much appreciated!

    Project Amazon showing air vent locations(from Eric):

    Attached Files:

  15. HJS
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    HJS Member

    Midship interceptor v/s Dynaplane stepped hull

    These two options are based on completely different principles and are therefore not strictly comparable. Both just need the ventilation in the transition between the low speed with only static lift and higher speed with static and dynamic lift, planing. There is no question of any air lubrication, the boat just planes on a surface in front of the step or the interceptor. The rear stabilizer takes a portion of the lift and balances the fore and aft trim, the front surface angle of attack.

    Dynaplane has a limited speed register in which it is effective. Moreover, it assumes that it goes upright, can be difficult to work when the boat is heeled. If the stagnation line goes over the step the flow will connect behind the step and wet much of the aft body.

    An adjustable mid-ship interceptor can be adapted to the need for lift both transverse and longitudinal. It is also not dependent on that the stagnation line must go over the chine or that the planing surface must be symmetric.

    In order to keep the boat in the right longitudinal trim the stabilizer must be adjustable all time. With my experience, it is not automatically done with a surface piercing V-shaped hydrofoil. I would choose a T-foil with manual flaps to control the angle of attack all time. On a sailboat all the centers of pressure moves all the time, depending on the wind variations. The design must be flexible so that it's in balance all the time.

    Hope I contributed something. Sailing is complicated to explain, especially in a foreign language for me.

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