Are they using aerodynamic lift yet in the America's Cup?

Discussion in 'Boat Design' started by jakeeeef, Nov 10, 2021.

  1. jakeeeef
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    jakeeeef Senior Member

    I guess it's very rules dependent, but at 40 mph+ surely you're getting into the realms of minimizing water foil size a bit and making the bridge deck a bit of a wing? Or a lot of a wing. The aparrent wind is so far forward at that speed.

    It's not even really extra material to add when it's a cat. You've already got cross beams, or a bridge deck, so why don't they do it? Or do they?

    It's why I posted the thing about a month ago about whether anyone has done a sailing ekranoplan.

    The idea of a sailing boat getting a decent amount of wing in ground effect lift is still very exciting to me!

    I guess it would need tapered inclined foils rather than L foils so it has a bigger lift area at slower speeds, so it can build enough speed on hydro to bring the aparrent far forward enough to start funnelling between the hulls and giving that magic WIG lift?

    Imagine the accidents they could have! They could get the 'full Donald Campbell' when that lift gets a bit out of control. Better for telly!
  2. jakeeeef
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    jakeeeef Senior Member

    Wouldn't work for anything other than sheltered water, hence America's Cup.

    The moment the air wing hit a wave tip any benefits would probably cancel out.

    And for WIG, wing would be pretty low down. Maybe that's why they don't do it?
  3. Robert Biegler
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    Robert Biegler Senior Member

    One minute in:

    I don't think Sail rocket 1 was designed for the beam to lift. Sailrocket 2 maybe. Beam and sail were placed aft, meaning that if beam and sail lifted, the boat pitched down, decreasing the angle of attack.

    I think aerodynamic lift needs to deal with the following:

    Best lift to drag ratio is unlikely to differ between an airfoil and a hydrofoil, but the hydrofoil is already built to hit the water. If an airfoil, built for a medium 1/800th as dense hits the water, there will be damage, unless it is built much stronger than it needs to be for its lifting function. Also, the hydrofoil can be smaller, so lever arms are smaller, and the foil should be lighter.

    If there is flow across the span, which will happen unless you turn your airfoil into the apparent wind, and the boat heels to lee, in most configurations, that will increase the angle of attack. Unless the airfoil is to lee of both the centre of gravity and the origin of whatever other forces hold the boat up, that decreases stability.

    Will the hull(s) or fuselage point directly into apparent wind? If not, what will that do to flow over you airfoil? If they do, what happens if the boat drops down into the water? If you rotated the hydrofoils under a catamaran by 20 degrees, so the hulls point into the wind and the beam gets a clean airstream to lift the boat, what would happen when the boat drops off the foils and the hulls hit the water at 40 knots and a 20 degree angle of attack?

    One concept that apparently does intend to use a wing in ground effect is the V-Rex foiler: Emission-Free Speed Record and offshore transportation!

    As far as I can tell, the boat is heeled to windward enough that the windward wing normally supports part of the weight. If the boat heels to lee, the ground effect diminishes, and the boat gains stability. Up to a point.

    In the following, taken from the description on Kickstarter, there either is a bit of salesmanship, or the inventors mean the claimed uniqueness to apply only to the combinations of all parts of the statement: "In contrast to all other known sailing boats, V_REX leans to the windward side which converts sail pressure into propulsion and uses a ground effect wing for stabilization, which enables stable flight." Converting sail pressure into propulsion is what all sailing vessels do, no matter which way they heel. Windsurfers have been leaning to windward for decades, and foiling dinghies at least since Rohan Veal. Combining that with a wing in ground effect to get at least some passive stabilising feedback does seem to be new. I am guessing that most of the active control is through the flaps on those wings and by steering, with energy-intensive control of sheeting being a last resort. They don't explain that.

    They also say: "The stabilizers are arranged in a V- shape at a 33° angle to the hull, with a 250 L water tank at the tip of each for water- ballast. Those tanks can be filled within a few seconds through a system known from firefighter planes. During maneuvers the water is routed from the leeward to the windward side through a pipe system."

    In the time I was willing to invest, I couldn't find a description of how firefighter planes take on water. I guess it's ram pressure. If so, that needs speed, and if you want that weight to windward immediately, you would need the boat to sail at speed already heeling to windward. Perhaps they plan to fill up the tank to lee, then tack or gybe. And shifting 250kg from side to side in a few seconds would take a lot of power. Perhaps they plan to pump a bit more slowly, while depowering as much as needed, then tack or gybe, then finish pumping. Or perhaps the ballast is only needed to heel to windward while getting up on the foils, and from there on, the weight of the boat and payload is enough. They don't explain those details.

    I don't understand at all what is supposed to make that concept more suitable for cargo transport than supporting the weight by buoyancy. I would have thought supporting the weight on foils is only worth the bother for light weights that should spend little time in transit, which fits passengers better than cargo. I expect the lift to drag ratio of a container ship or a large tanker is hard to beat, so I don't know what foils offer unless time in transit is critical, and then air transport has advantages, at least over long distances. Even taking environmental impact into account does not obviously favour hydrofoils. I expect that the cargo capacity of V-Rex is less than that of existing displacement hulls, which would mean more vessels, and more risk of collision with wildlife. Even total noise pollution might not be less. Those foils are not totally silent. The sound spectrum might shift, compared to engines and propellers.

    I think the concept is interesting. I would like to see it sail. I am not persuaded that it has potential as a cargo carrier.
  4. jakeeeef
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    jakeeeef Senior Member

    Wow, that Kickstarter boat has a lot of moving parts for him to get his head round.
    The leverage those wings with weighted bulbs would generate just looks like it would be unmanageable. The moment one of those touches the water, it's either snapping off in a shower of carbon dust or its providing a dramatic pivot point for the whole shebang.

    The system that the firefighting planes use is basically a hinged scoop or chute sometimes with a bit of a NACA vent if I remember bit like a dinghy self bailer the wrong way round. In the context of a lightweight sailing boat, a very effective brake I'd imagine.

    As you point out, leaning a sail to windward is nothing remotely new.

    The catamaran concept is a way better one in my view. Shame I don't have the CGI skills to pull a quick 5 grand off Kickstarter with it!

    Yes, yawing the whole boat to align with aparrent wind could be achieved with the water foils.

    Doesn't require additional ballast.
    Already has a structure between the hulls so the weight 'cost' of incorporating a wing is much lower than adding additional wings to a monohull.
    Has the beneficial end plate effect for the wing, provided by the hulls' inner surfaces.
    It's also already flying vaguely horizontally esp concerning roll. It's a much more 'foursquare' platform on which to put a wing and therefore much more closely control variables such as the pitch angle.

    That guy's Kickstarter is a ladder on a skateboard, while riding a bike I'm afraid, but I do like it that he's getting out there and trying to do something with it, and I'd love him to prove me wrong.
  5. jakeeeef
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    jakeeeef Senior Member

    Re: foiling cargo boats.
    There's been a few on crowd funding sites I hear.

    One, a 300m cargo ship on foils I hear pulled in a vast sum of investment!

    It did not pass muster on even the most basic mathematical consideration.

    People look at what companies like BAR and Artemis Technologies are doing and assume it is where things are headed and the technology endlessly scalable. Or more cynically think that others will think it is and buy into the idea.
    But what these specialised companies are doing they will tell you themselves is very, very difficult to scale up.

    Back in the real world, Artemis has spent millions of funding and over 3 years developing its foiling technology and is about to launch and demo its first publicised prototype. It is an 11m workboat.
  6. Will Gilmore
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    Will Gilmore Senior Member

    They could use the sail for lift. Putting a kite sail on the boat would reduce the heeling effect of the sail and lift the hull.
  7. messabout
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    messabout Senior Member

    ^ Fascinating rig, Will.

    Might be a challenge for the skipper when trimming or "tilting" the sail. That has gotta be great fun to experiment with. It appears that the spars are made of PVC pipe. The maker of that thing was being pretty clever. If all else failed, the "sail" could be rigged horizontally which would provide sunshade for the fisherman. Sure enough the whole thing has the potential for creating some lift.

    The dinghy looks pretty good too.
    Will Gilmore likes this.

  8. Will Gilmore
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    Will Gilmore Senior Member

    Here's another example and a link.
    3 m Proa: Katamaran - Trimaran - Proa

    I believe this concept holds a lot of potential. Let it out on a tether and it's a kite sail.
    Bring it in to the top of the mast for more control sailing to windward or act as a fore-and-aft rig. Could also become a square rig.

    Reef by tilting it or fold it up against the mast.

    Shade. I hadn't thought of that advantage, but yes. Maybe an emergency drogue too.

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