Sailing Foiler Design: Foil Assist and Full Flying

Discussion in 'Hydrodynamics and Aerodynamics' started by Doug Lord, Dec 9, 2011.

  1. Doug Lord
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    Doug Lord Flight Ready

  2. Doug Lord
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    Doug Lord Flight Ready

  3. brian eiland
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    brian eiland Senior Member

    RAVE V vessel, foil-borne and A-frame rig

    Hi Doug,
    Have you seen this latest presentation video on the new foil-borne, A-frame rigged vessel, the RAVE V ?

    This new foiling vessel with an unusual A-frame type rig has come up on another forum,...VERY interesting foiling and rigging subjects.

    Foiling Week™ 2015 - Forum day 2 - Larry Knauer
    https://www.youtube.com/watch?t=228&v=JD5-shtZalY
     
  4. brian eiland
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    brian eiland Senior Member

    a few more links provided by this German fellow over on the other forum...
     
  5. Doug Lord
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    Doug Lord Flight Ready

    Yes, it is a Revolution!

    These are exciting times for anyone interested in foil assist and flying on foils! Long ago I thought something like this would happen but the AC72's were (almost) beyond my wildest dreams. And Hugh's flying keelboat(Q23) is the first such keelboat in the history of the world!
     
  6. brian eiland
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    brian eiland Senior Member

    I will have to admit it, you were one of the EARLY believers in foiling technology.

    And it does appear as though the America's Cup has spawned a great deal of interest in the subject.
     
  7. Doug Lord
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    Doug Lord Flight Ready

    SNAKEfOIL

    Steve Clark has come up with a new type of foil, or perhaps a new application for half of an old foil configuration. This is a single surface piercing foil that generates lift to weather in addition to vertical lift. In the past surface piercing main foils were used together -one on each side. This has several potential advantages and is most likely a significant step forward in foil configuration design. Compared to some UptiP foil designs, surface piercing foils may have more variance in altitude due to speed. Using a single surface piercing foil as a SINGLE main foil is new to me and I imagine it is probably a first. See the Hydroptere pix below-short term flight on a single main foil.
    Steves comments on the foil:
    1) SNAKEfOILs: Low drag foil solution which can be pulled all the way up on the windward side.
    Longer span, less induced drag, less spray and parasitic drag plus we don't have to fly 1 meter in the air. Splashes are much less dramatic as a result.
    Down side is the center of lift is further inboard, so we give up some righting moment. Foil also works near the surface and can ventilate if we don't pay close attention.
    ====================================
    2) The design is heave stable by the same mechanism of most surface piercing foils. The foil surface becomes less efficient as it getys closer to the surface, and therefore delivers less lift. There is a reflex curve in the span, which means that the foil loses horizontal projected area faster than it loses vertical projected area. We can adjust the ratio by deciding how far to let the blade rotate as it extends. There is an worm gear which adjusts the angle of attack of the foil, much like on every other catamaran. Unlike the Melvin foils, we do not use leeway to control heave. We also don't have the tip breaching the surface.
    We have had some trouble with the boards over producing side force when sailing down wind, so sometimes we saildown wind with the weather board down about 2 feet. This isn't optimal, but we have had some very nice rides at very deep angles. Upwind, over producing side force isn't the bummer it used to be when the hull was in the water. In fact there is absolutely nothing wrong with crabbing to windward as long as you are foiling.
    The ride is really amusing, it's kind of bouncy, I guess because the foils bend and there is a bunch of visco-elasticity in the water. This is unintended, but could be cool in a sort of trampofoil flapping foil way. All in all, way too much fun for someone my age.
    SHC
    -------------------------------------------
    In reference to the foil illustration showing multiple positions:

    3) As you can see it acts just like an deep asymmetrical dagger board until we engage the head. Then it becomes a canted surface piercing foil.
    A subtly is that the radius under the hull gets it deeper than if it was simply inclined in a straight trunk.
    The head of the board is also symmetrical, which makes it quite fat for structure, but also reduces lift right at the surface, so it is less likely to gulp air. It also makes the boat more docile as the waterline travels up and down the curved span.
    The reflex curve is so that the foil loses vertical projected area faster than it loses sideways projected area as the boat rises out of the water. We only intend to fly 12" or so in the air. Lots less windage down there. And the bow and stern are a whole lot more useful when things go wrong.

    Paul Bogataj deserves all the credit for taking my various musings, observations, prejudices and observations and turning them into a coherent design. It is said a million times that design is all about compromise, inn this case I was willing to surrender righting moment for less drag and to not have extra wetted surface in light air and the giant sucking sound when the windward hydrofoil breaches the surface during the most critical part of the speed build.

    Erich Chase built the boards, and did his usual great work.

    It should be fun to see what happens if we get any wind at all.
    SHC


    [​IMG]

    Steves C Class Aethon using the SNAKEfOIL , Hydroptere flying for a short period on one main foil and Steves illustration of how the foil fits in the trunk:
     

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  8. Gary Baigent
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    Gary Baigent Senior Member

    Of course you are joking, Doug?
    One main foil (plus rudder T) flying the boat. Have you been blind to 5 decades of foil history?
    Just because you have convinced yourself that platforms require 3 or in your case 4 or more foils to fly, does not mean that large numbers of foilers adhere to your fixation.
    Not going to make a long list of examples but will go back to the earliest days of flying foilers, like the 1960s: here is Eric Tabarly's experimental pre-Paul Ricard and Thebault's pre-Hydroptere model. I suppose you will say the windward foil is immersed, but it isn't just the very tip but even that is lifted clear at the moment the shutter was fired. So how many working foils: 2.
    This is not last week and suddenly discovered by you - but decades ago.
    Strange how the latest fashion can take over from historical reality?
     

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  9. Doug Lord
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    Doug Lord Flight Ready

    SNAKEfOIL

    Gary, my boat foils with three foils in the water, but the main foil unloads 100 % as the boat speeds up.
    Hydroptere would fly the windward foil(see my last post) now and again but wasn't designed to sail on just two foils. Steves foil configuration is significantly different than other surface piercing foilers I've seen because it is designed to fly on a single main foil + two rudder foils and be stable doing so.
    In the picture you posted you can clearly see the wake from the windward foil that was immersed and fly's intermittently like most three foil surface-piercers. It seems to me that when a three foil surface piercer rotates on an axis between the rudder and lee main foil that it has to change the angle of attack of the lee main foil which could cause a crash, couldn't it?
    PS-it also increases the angle of attack of the rudder foil..... On Steves system(and mine for that matter) the AOA remains the same with heel....

    Fire Arrow:

    [​IMG]
     
  10. Gary Baigent
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    Gary Baigent Senior Member

    When Hydroptere is at maximum speed, only the tip of the windward foil is in water; she is supported by near 100% by the main lee and lee rudder foils. The windward foil tip kissing surface is doing zero, just fractional drag.
    I mean lets go back to basics; take the AC45 cats: their windward foil is right up and their windward rudder foil is doing sweet FA (minor drag of the inverted T area) - all the lifting work is being handled by the lee main and lee rudder.
    The windward rudder, if the cat begins rolling to weather, will help stabilize the platform a little, yes - but when the boat is at top speed (for the conditions) and balanced, you can say only 2 foils are doing the hard work.
    Your model's main hull central foil will NOT unload, it will be working (and if not working as you claim) will be dragging. You cannot make wetted surface disappear. And in your case, very large wetted surface areas.
     
  11. Doug Lord
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    Doug Lord Flight Ready

    Gary, just out of curiosity, do you have any pictures(and or video-even if its only 15 seconds)of any of your foilers foiling with the main hull clear of the water?
    Oh, and by the way-the wetted foil area of the Fire Arrow when its foiling is not any greater(and may actually be less) than any other wand based foiler of the same weight......
    Drag is most certainly less when the mainfoil is unloaded*.......
    *Unloaded means that there is no induced drag(drag due to lift)-it does not mean there is no drag from other drag sources.
     
  12. Gary Baigent
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    Gary Baigent Senior Member

    No, not at high speed because I'm usually sailing solo and haven't yet figured out a system of shooting cameras while steering/sheeting.
    Yes, could put gopro on helmet but haven't done so as yet.
    However check Sid's wake in 4 - 5 knots wind and check out lee foil wake - you can work out how little main hull is in water - then imagine 12-15 knots wind strength.
     

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  13. Doug Lord
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    Doug Lord Flight Ready

    Surface piercer

    Excellent picture of a model surface piercer* illustrating the increase in angle of attack of the lee main foil and rudder foil with heel:
    *configuration: two main foils, one rudder T-foil.

    [​IMG]
     
  14. Skip JayR
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    Skip JayR Tri Enthusiast

    wowh.... DougL, thats great work and good intention. I suppose it takes me some weeks to go through all that foil stuff to digest.

    For me the most interesting question is: "Under which circumstances an "old Trimaran" can be equipped, or better let it say "being pimped up" to turn into a competitively boat" ???

    I am sure, that many owners out there have this question in mind. Not all can (or dont want) afford to let build a new G4 Gunboat at a prize of 2-3 million US Dollars.

    There are many smaller and excellent boats out there, catamarans or trimarans whose owners are waiting for some good and prizely foils (daggerboards in the amas) to be equippied for better performance (inclusive T-/L-Shaped rudders), as their bow segments neither can be reshaped into a "wave piercing knife" nor the volume of the ama can be expanded to give more uplift for compensating a weak righting moment of the original design at higher speeds and bigger sail wardrobe/mast.
     

  15. Doug Lord
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    Doug Lord Flight Ready

    Sailing Foiler Design

    Thanks, Skip. Just to be clear that model surface piercer is not one of mine though I published the free plan for it (from Foilers!) in my thread in Multihulls.
    There is tremendous potential for the application of foils to trimarans-even some older ones- both foil assist and full flying. Larger trimarans have shown that they are faster than equal length cats and I'm interested in seeing trimaran designs under 20' do the same thing-and they will sooner or later.
     
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