Sailing Sci-Fi

Discussion in 'Boat Design' started by DFV, Feb 27, 2007.

  1. DFV
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    DFV Junior Member

    Has anyone tried to create a set of fins on the hull of a sailboat.....where when heeled, let's say, 10-12 degrees, one fin would be out of the water and the other still in,....AND.....the fin in the water would have a shape which would work against the heel of the boat, trying to right it? The fin might be a long flap horizontally placed along the hull, with a flare at the front, progressively getting closer to the hull along its length. As the water passed along it, a force would be created trying to cancel the heel.
    I assume, like just about anything else one does to a hull, that the added drag would cancel out any advantage, but I thought I'd ask anyways. It seems like using the power in the 'flowing by' water to work against heeling might be a good idea.

    What say yee all?

    -ray-

    (Those stabilizer flaps on the 44 MLB's got me thinking.)
     
  2. kach22i
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    kach22i Architect

  3. Doug Lord

    Doug Lord Guest

    Righting Moment

    The guys that invented CBTF have another patent on a system that uses a canting keel with significantly reduced ballast. The ballast less than on a "normal" canting keel boat because the ballast strut uses a flap to create downforce when the keel is at max cant(55°) . The big downside of using any kind of foil to create RM is induced drag so the foil has to be well designed to maximise the gains in speed by reducing the losses in drag. Most foils that are used to do this seem to have the center of lift of the foils as far from the centerline of the boat as is practical for the particular design.
    There are other boats that utilize a concept similar to yours(as I understand it) including a neat 16' proa that uses a foil on one side to create righting moment and the Hobie trifoiler and Rave hydrofoil which get most of their RM from the action of the hydrofoils.
    -----------------
    Note on Hydroptere- Hydroptere is a surface piercing foiler which means it doesn't use an altitude control system. This is important since on the Rave and Hobie trifoiler the foils are fully submerged and each main foil has its own altitude control system. On these boats it is the differential action of the altitude control system that allows the main foils to control RM(and lift). On Hydroptere the boat's weight plus its on-board water ballast creates righting moment. Different foil systems different-different methods of achieving RM.
     
  4. Vega
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    Vega Senior Member

    Doug, I can figure out a large monohull that can sail at speed over foils. It can work, as you have suggested with mobile ballast that can be moved outside the boat, like the weight of people on a trapeze in a dinghy sailboat. But when the boat tacks it would be unacceptably instable and I can not see how it can be fixed.

    I believe the only way to go would be with a kind of fake trimaran. I say fake, because it would not work like a trimaran. It would have a large central hull with water ballast (kind of open 60) with foils and two thin amas, far away from the central hull and raised above the water. They would only touch the water at 13º or something like that.

    The boat would not work like a tri, because it would fly most of the time, and would be sailed with both amas in the air. The rightening moment would not be provided by hull form, but by a movable ballast that could be moved fast between the two amas, that would be much more far away (from the central hull) than in a trimaran. If the amas are adequately separated, a relatively small ballast can provide a huge rightening moment.

    The only time those amas would really work would be when the boat changed tack, or when sailing with wind from behind, giving support to small instabilities.

    How about a model;) ?
     
  5. Doug Lord

    Doug Lord Guest

    Monofoilers

    Paulo, I disagree about having an Open 60 type main hull because that would adversely affect the speed at which the boat foiled and the wind it would take to get the boat on foils.A monofoiler is quite stable in a tack as long as it keeps moving-buoyancy pods and a fast movable ballast system are backup if it doesn't keep moving. I think the boat I've described in the 60' monofoiler thread(under sailboats) is the way to go and I'm in the process of building a smaller version with some differences but utilizing essentially the exact same concept(X18T thread under sailboats).
    You're 100% right that such a boat needs some buoyancy at the widest point of its beam but in order to be accepted as a monohull that buoyancy can't resemble hulls or ama's. On the 60' monofoiler both a canting keel and sliding on-deck water ballast are used. The canting keel is only there to make the boat rightable....A multihull version would look identical to the monofoiler but wouldn't have the canting keel and the on-deck sliding water ballast would be heavier. The multifoiler version would have slightly larger buoyancy pods outboard- perhaps resembling mini amas like on Hydroptere and would probably not be rightable as is the monofoiler.
    Go to www.microsail.com and note the movable ballast system on the Melges 24RC and click on "MONOHULLS" and follow that to the microMOTH....
     
  6. DFV
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    DFV Junior Member

    Most of my question was directed at a sailing vessel which encounters a huge heeling force. I like the idea of having only one fin or foil in the water at a time (so the other fin wouldn't cancel out the effect). Whichever way you lean, you have the correct foil producing the effect, and the other is non-effectual. You heel to port and the starboard fin leaves the water. The port fin creates a force against the heel, from the water within 4 or 5 inches from the hull surface, along the hull for about 2/3 of the waterline length.
     
  7. charmc
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    charmc Senior Member

    Some unique variations:
     

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  8. kach22i
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    kach22i Architect

  9. LP
    Joined: Jul 2005
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    LP Flying Boatman

    Bilge fins.

    Going back to the original question, I saw it more as supplementing a basic monohull that has been optimized for the use of "bilge foils." See attached .jpg. I've played with the idea for use in something beachable. The fin keel is replaced by the bilge foils that would also provide lateral resistance. I was toying with curved foils that have a constant radius spanwise. The constant radius would allow the boards to extend and retract while keeping the lift force vector away from the bilge slot and further from the hull centerline.

    In this picture, I was just trying to draw the foil in freeship and threw it onto an existing hull that's not optimized for the application. I'm trying to visualize what the optimum hull would be for such a design. I don't think you could "fly" the hull so the bilge foil would either assist in unweighting the hull to a point where it would plane or it would unweight the hull to where there was at least a significant reduction in wetted surface. Perhaps, that's overly optimitic and just increasing the righting moment to keep the sails powered would be more realistic. Maybe to allow for a more slender body hull design. To serve it's purpose though, I would think that it would have to hull drag by at least as much drag as it adds, more so to be of any use.

    This is all "what-if", but I'd certainly be curious to here everbody's thoughts.
     

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  10. kach22i
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    kach22i Architect

    Nice, and that looks like what was described too.:)

    Reminds me of a Killer Whale.
    [​IMG]

    EDIT.................or the Bionic Dolphin.
    [​IMG]
     
  11. DFV
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    DFV Junior Member

    If I may, let me add a graphic to try to be more clear. The boat just shows WHERE these fin/foils might go, and the drawing tries to show HOW it might bend/twist, in order to get some force from the flow of water. There seems to be some elegance to the idea, but my knowledge of hydrodynamics is limited. Thanks to all for the serious input.
    (One of these days I'm going to have an idea which isn't moronic.)
     

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  12. Doug Lord

    Doug Lord Guest

    lifting strake?

    DFV, Eric Sponberg desgned a very fast ocean racer using a sort of step in the side of the hull. I'm hoping he'll stop in here with more details...
     
  13. Eric Sponberg
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    Eric Sponberg Senior Member

    DFV,

    What you are describing is lifting strakes. I have designed these for both power and sail boats. For a complete study on one project, you can see my website for the modifications on Blue Bill:

    http://www.sponbergyachtdesign.com/Bluebill.htm

    I also attach a photo below of Blue Bill. As the story tells you, these worked extremely well.

    I also put lifting strakes on my Open Class 60 Project Amazon. Photo attached below. These did not replace the keel. You still need a keel to counteract the heeling moment from the rig, so there really isn't any way around that. But the lifting strakes on Project Amazon allowed her to get up on plane and stay on plane for long periods of time. The owner said that Project Amazon could be frightening to sail sometimes because it just wanted to get up and go at 25 knots all the time, and there were some times that you did NOT want to go 25 knots, 12 knots would do just fine. Lars Bergstrom, one of the founders of B&R Mast & Rigging (now deceased) told me that he thought Project Amazon would be too fast! Indeed, it was.

    As I have mentioned before, I do have a pdf copy of the technical paper that I wrote for SNAMEs Marine Technology magazine that completely describes all the features of Project Amazon, including the lifting strakes, air lubrication system, the free-standing rig, the canting keel with the built-in trim tab, the retractible rudders in a drum, etc., everything. If anyone would like a copy, you may write to me directly and I will be happy to send it on for free. It is a pretty big file, over 7 Mb, so it might take a while to send if you have a slow internet connection.

    Regards,

    Eric
    ewsponberg@sponbergyachtdesign.com
     

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  14. safewalrus
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    safewalrus Ancient Marriner

    kinda like 'bilge keels' or 'lee boards' maybe? gee that's new!
     

  15. Vega
    Joined: Apr 2005
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    Vega Senior Member

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