MastFoil, opinions?

Discussion in 'Boat Design' started by Krauthammer, Nov 6, 2011.

  1. Krauthammer
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    Krauthammer Junior Member

  2. Krauthammer
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    Krauthammer Junior Member

    To be clear, where is the lift and drag that we have on conventional sails/airfoils generated and how is the MastFoil sailing to windward as seen in one of the videos?
     
  3. Doug Lord
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    Doug Lord Flight Ready

    Attached Files:

  4. Krauthammer
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    Krauthammer Junior Member

    Thank you for the link to what appears to be a good thread.

    One of the videos on the MastFoil shows the cat sailing to windward under main alone. Maybe after reading the thread I will be closer to understanding how this works.

    BTW where can I read more on your self righting trimaran? A tri is the design that I am researching for a singlehanded long range application where sail handling is reduced/self tending under most conditions.
     
  5. Doug Lord
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    Doug Lord Flight Ready

    ------------------------
    You can find the Test Model thread and a quick summary here in post 137:
    http://www.boatdesign.net/forums/mu...lf-righting-trimaran-test-model-36058-10.html
     
  6. upchurchmr
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    upchurchmr Senior Member

    Anyone know Chris White and can get him to comment? Since he has a Patent Pending shouldn't be a threat to his supposed intellectual property rights. Perhaps he would get free advertising. Much earlier he had a patent for a leaning mast on a daysailing cat. Never saw anything about it again. Good, bad, or.....

    This would be more interesting if we could know the MastFoil area, boat speed vs wind speed, and a few other things. Looks like you could plant 3 of those in a row and have plenty of separation to make them work. Or stick them on Catbird Suite as the bipod masts.

    Of course area makes up for almost everything downwind. Doesn't look like the MastFoil would work well by itself. I suppose a spinniker would solve that.

    Interested in some actual data.

    Marc
     
  7. Krauthammer
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    Krauthammer Junior Member

    These are the important facts indeed.
     
  8. eiasu
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    eiasu Junior Member

  9. tspeer
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    tspeer Senior Member

    Try this link instead: http://www.chriswhitedesigns.com/atlantic_cats/mastfoil/index.shtml

    I think the concept has a lot of merit. However, some of the statements on his website are rather doubtful, to say the least. Among them are:

    "The MastFoil never stalls." - Any wing will stall at a high angle of attack. I doubt that fully attached flow can be maintained at an angle of attack greater than 35 deg to the trailing edge bisector, and if there is no slot, the stall angle would be considerably less than that.

    "Pinned to the dock by a 30 knot wind on the beam? We think that by trimming the MastFoils opposite each other that enough sideways lift can be created to actually pull the boat away from the dock!" - This is rubbish. A wing produces both lift and drag. For sure, the lift components from the two masts can oppose each other, but the drag components would add to each other, not be subtracted one from the other like the lift. There is no way a wing can produce a total force component that is forward of 90 degrees to the apparent wind. That's what would be required to pull the boat upwind away from the dock against a beam wind.

    "If you are running off in a storm the MastFoil can function as a "air drogue" by providing stern-ward thrust to offset the windage of the hulls and deckhouse." - On a dead run, this also requires the wings to produce a force that is to windward of 90 deg from the apparent wind, with the apparent wind in this case being from astern. The wings can be rotated 180 deg so their leading edges point into the wind, minimizing drag, but their drag will still be propelling the boat, not slowing it down as an "air drogue". And, of course, if the wings are trimmed in opposite directions, their longitudinal separation would result in a considerable yawing moment that has to be countered by the rudders (which may already be sorely tasked by the waves).

    When on a broad reach, provided the boat is sailing a high enough course, the wings can be trimmed so as to have a rearward component of the lift. The aerodynamic picture would be essentially the same as when beating to windward. The difference is the boat's velocity through the water would be reversed and the leeway angle on the keel/board would create lift on the keel to balance the side load from the wings. So it's true that the wings could slow the boat for a range of offwind angles. But it's more akin to sailing backwards than it is to deploying a drogue. There will be a heeling moment associated with it, and it won't work when sailing very deep.

    As for the behavior of the wing in a storm, just because the wing's aerodynamic center is behind the pivot axis doesn't mean that it will weather vane to zero lift or to minimum drag. There are two issues here: camber and dynamics. If the wing is freely rotating with camber set, it will trim at a negative lift (compared to the direction of the camber). This has almost led to the capsize of AC45s when tacking - friction in the control system prevented the wing from flatening naturally and the wing flew itself on to the other tack with the traveler control lines slack. The boat flew a hull by itself, but the crew were able to steer down to get it under control.

    Dynamically, the mastfoil needs to have its pivot axis at or ahead of the quarter chord for static aerodynamic stability, and it needs to have its center of mass on or ahead of the pivot axis for dynamic stability. If the first condition isn't met, the mast won't try to weathervane, and if the second condition isn't met, the mast may flutter or be swung about in a seaway. Either outcome could result in more windage than a conventional mast, to say nothing of the violence a fluttering mast can do. It's not clear from the illustrations how these considerations are being handled.

    The pivot axis does appear to be well forward, so I believe the mast has some static stability. There are no forward-projecting balance arms shown, so if the mast is mass balanced, it may be done with a considerable amount of structural material in the leading edge. However, the description also talks about the stays having a stable position, which implies there is a round central structural member and an outer rotating shell. It's the shell that has to be mass balanced, and the bulk of the structural weight would not contribute to that. This may require lead ballast in the leading edge of the shell. (Tungsten is also used in aerospace to mass balance control surfaces, as it is denser and harder than lead.)

    Even if the wings are aerodynamically stable and mass balanced, the dynamic response of the wings to rapid gusts in a gale needs to be carefully considered. Without a tail, the static margin (distance between the pivot axis and wing aerodynamic neutral point) would be small. Aerodynamic damping goes as the square of the tail length, and since the wing is acting as its own tail, the aerodynamic damping would also be low. This means the dynamic behavior would have a low natural frequency and be lightly damped. The wing may be slow to respond to a sudden gust and tend to overshoot and oscillate. If it is out of phase with shifty gusts, the lift and drag on the wing can be enhanced, not neutralized. The wing would be trying to weathervane, but it may be constantly playing catch-up instead of maintaining the zero angle of attack envisaged.

    This is all speculation on my part, and I don't mean in any way to disparage the Wingfoil concept. I have a lot of respect for Chris White's designs (after all, my own boat is a Chris White designed trimaran). I just wonder to what extent these considerations have been engineered into the design. The same considerations led to sizable tail surfaces and forward balance arms on the Harborwing X-2. To get the same good behavior in a blow without tails and balance arms would require some innovative solutions - perhaps they will be described in the patent.

    Adding tails and balance arms isn't a trivial issue, either. The tail on the forward mast can be located above the forestay of the aft mast and under its own forestay and shrouds. But the proximity of the sail would present an obstacle to mast rotation. It may be that when the sail is trimmed closehauled, the mast doesn't have to rotate very much, and when it does need to swing to large angles, the sail will either be eased way out or furled. So the combination of wing and soft sail requires some interesting tradeoffs in the concept of operations, too. Striking the right compromise is what makes good design an art!
     
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  10. P Flados
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    P Flados Senior Member

    Although I am very fond of wings, I am also quick to note when my better (on this subject) has spoken.

    It is nice to see someone much better at wings than I noted the "smoke and mirrors" claims that bothered me.

    The suggestion about an A Frame on a multi (catbird suite) is also something I had thought of. To me, this seems to be a great matchup for wing shrouds on round structural masts.

    Gust response is an interesting topic worth discussion.

    I understand why there are big tails on Harbor Wing, but somehow I just do not like them. Although they may good technical solutions to a given problem, I am not sure that they are something that would ever be accepted by Joe Average Sailor.

    If the wing is configured to require low effort for rotation, it would be possible to design a a mechanism uses small movements of the overall wing in reasponse to a gust to change AOA. I can also see room for an active control feature that uses a separate wind direction sensor and boat roll angle to make the slower adjustments for general trim.

    If the wing/mast surface area is not large (head-sail is the biggest source of drive in normal sailing) gust reasons may be less of an issue.
     
  11. tspeer
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    tspeer Senior Member

    From the description on the web page, it's not clear whether the wingfoil is free to rotate in response to the wind, or if it is positively controlled to a fixed position. It may be both - positive control while driving the boat, and free to rotate when under bare poles and the objective is to simply minimize the windage.

    Relying on active control for a cruising boat would be very problematic. Such a control system has to have a high availability for safety. That means redundant hardware, redundant power sources, etc. I would much prefer a system that could could operate in a purely mechanical mode, with manual input. The Harborwing tails provide that capability.

    When some friends and I built a landyacht with a rigid wing and tail, we found that just having the wing aerodynamically balanced by the tail made it easy to simply hold the wing in the desired position. This proved the be the preferred method of control for racing.

    The gust alleviation of the pure aerodynamic control using the tail was quite effective. This wing had a small tail on a long arm, so it had good aerodynamic damping. The gust alleviation was too good for racing, because the boat did not get the burst of acceleration from the gust that it did when the wing was restrained.

    The tail and flap could be slaved together so when the tail moved one way, the flap moved in the opposite direction. This resulted in just one control for the wing to set the desired power, and the aerodynamic stability did the rest. We were able to sail the yacht in lighter winds with the aerodynamic control than with manual control, because the tail did such a good job of reacting to the shifting apparent wind. It would respond to puffs that I could hardly feel.

    I agree that the tails are not aesthetically pleasing and they have problems of their own as they sweep out a considerable volume of space, and that space has to be kept clear of obstructions. But they do solve some important problems with wing stability and control.

    I have pitchpoled a landyacht backwards when its wingmast fluttered during a tack. The proportion of mast area to mainsail area was probably around 25% - 30%. The relative size of the wingfoil is much smaller, but if it flutters in a gale, it can easily destroy the rig. Flutter is definitely preventable, but it can't be ignored.

    I think the mastfoil concept is a good one. But some of the claims being made make me wonder if it has been properly thought out.
     
  12. Krauthammer
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    Krauthammer Junior Member


    CW states: "Because the MastFoil can rotate freely (when the control line is released) the foils will automatically feather themselves into the wind, thus causing negligible drag and lift." wherein it is clear that the MF can be locked or be left free to rotate.

    He goes on to say: "We built a 60% size A47 MastFoil and sailed it in a variety of conditions on a smaller catamaran. After seeing how easy the MastFoil is to handle and how powerful it is in strong winds it was a "no brainer" to apply what was learned to a cruising size catamaran."

    The videos on his website are showing that boat and it is to be expected that a seriously interested party could be given the opportunity to experience the MF first hand.

    A CW Explorer 44 tri with the MF would be quite the cruising rig and if so designed one could replace the MF with a conventional rig in case the boat doesn't perform to expectations. I think that the MF holds a lot of promise for those who are looking for an easy to singlehand rig that makes sail handling an easy task while maintaining high performance attributes.
     
  13. brian eiland
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    brian eiland Senior Member

    I can't seem to find any videos related to the MastFoil vessel??
    Brian
     
  14. Krauthammer
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    Krauthammer Junior Member


    It is the last file in the RH column at

    http://chriswhitedesigns.smugmug.com/

    Unfortunately the file has been locked since I first posted the link in the OP. Call him and ask for a password, the videos are impressive.
     

  15. eiasu
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    eiasu Junior Member

    Does somebody has the password? Secretly could sent me a pm! :p:D:idea:
     
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