Planing Trimarans

Discussion in 'Multihulls' started by Doug Lord, Sep 30, 2006.

  1. Chris Ostlind

    Chris Ostlind Previous Member

    Well, Then...

    Even though that's a nice picture, Crag, it's not the same thing. The rig is entirely different and so is the way it is used in that configuration. It would be interesting to see a thirty foot tri with about ten guys hanging off the wishbone boom all synchronized in their movements with the boat.

    The photo below shows more of what is really happening on board a multihull. Do pay special attention to the windward hull as it planes across the surface under its own lifting properties.
     

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  2. Crag Cay
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    Crag Cay Senior Member

    My comment (in posts 212 and 215) related to the aero dynamic lift generated by a windsurfer with the rig canted to windward and a monohull running deep and trimmed upright. That's why I posted the picture of a windsurfer.

    And my question was, does the lift generated in these instances disqualify them (windsurfers and monohulls) from ever planing, as it would appear to contravene the stated definition that planing must be by 'lift from hydrodynamic forces on the hull only' ?
     
    Last edited: Nov 22, 2006
  3. PI Design
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    PI Design Senior Member

    The claim, quite unambiguously, was that only a kite surfer produced an upward aerodynamic force. I think Crag has shown that this statement is patently not true. How can anyone claim that an asymmetric kite produces a downwards force? Look at a 12ft skiff video (loads on the web). It clearly produces an upward lift force, which unloads the hull. By the arguments used in this thread, that would preclude it from planing (and of course, the windsurfer in that picture).
    I don’t think anyone has claimed that a cats windward hull is planning, purely because it is has a shallower draught than the leeward one. Planing, as I have pointed out repeatedly, requires a stagnation point. This, in turn, usually requires the bow to be out of the water, so that the water’s surface can strike the underside of the hull. In your picture this is not happening, so it is not planing.
     
  4. Chris Ostlind

    Chris Ostlind Previous Member

    Please find the link below and enjoy the read.

    http://www.sailingsource.com/cherub/aero.htm

    If you have access to an F-boat, here's a simple experiment you can run to get a better idea as to the dynamic forces involved.

    Take her out on nice breezy day and observe the placement of the crew on the boat for best performance upwind. Now, turn offwind and fly an assy chute for optimal trim and apparent wind. Leave the crew at the same location on the boat and see how long you can fly the chute nicely sheeted-in without pushing the bow of the leeward ama under water and scaring the crap out of everyone onboard, much less the owner of the boat.

    Is that a lifting rig when parts start to go submarine and the crew runs for the aft parts of the boat?

    PI: I get all the stagnation point, etc., remarks about a hull that is supporting itself dynamically without assitance. It just seems to me that if you allow one hull to achieve planing condition due to severe unweighting onto another component hull, that you would also, and quite clearly have to recognize it as such for another type of multihull. The cat pictured is hovering at that point, give or take a degree of heel, and I would bet in the next image in sequence you would see the condition quite clearly.

    I know that when I raced my Nacra 6.0 that I could lift the windward hull ever so subtly to just kiss the surface of the wave tops, so the experience is well-known to me.

    Your argument is that there is a dynamic lift force on the vaka hull of a tri. Why can't there also be a dynamic lift force on the windward hull of a cat?

    In truth, I'm being facetious about both and you all know the reasons.

    Now, and at last, is everyone not in agreement that the topic has been exhausted to the point where we all recognize that there isn't going to be a resolved solution?

    What do you say we just drop this, dog-chasing-his-tail discussion and go on to some other nicely heated thread with a real potential for an agreed outcome? Then Will can quit bugging me about obsessing and Doug can go back to... whatever.
     
  5. mike leneman
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    mike leneman Junior Member

    planning

    I don't think there is any question that a canting rig, like a windsurfer, can develope upward lift. If you look at an upright rig, you will see that it's hard to develope much upward force.
    Now, I have no problem calling something planning if a major amount of the "lift" of the EFFECTIVE weight, is due to hydrodynamic forces....... I just don't believe there is on an F boat. Based on sailing them for 15 years, and probably much more time on them than the designer.
    Cheers,
    Mike Leneman
     
  6. peerliane
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    peerliane Junior Member

    Full scale experiment

    We are currently building a 50 foot trimaran that (we hope) will fly. Please , have a look at the pics of the construction and on design:
    www.utopia@lagoon .nc
    The main althought narrow is nearly shaped as a monohull, while the amas bottoms are flat like a surfboard. The purpose is to have lift on the forward part of the floats and the center of the main. Our concern is rather about the stress it will give to the arms when the ama hits a wave. The top of the amas bows is a vee upside down, in order to push water sideway to have a "smoother" passage. As anyone an objective opinion about this?
    In the 80's there where several foiler trimaran (Paul Ricard, Gérard Lambert, Downtown flyer...) with very short floats that sailed in balance on the buoyancy of the main and the lift of the leeward hydrofoil. Why couldn't we do the same with a planning ama?
    We'll get an answer soon; our boat will be in the water end of february...
    Thanks for anyone comment.
     
  7. Willallison
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    Willallison Senior Member

    Who said we wouldn't agree....:D
     
  8. peerliane
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    peerliane Junior Member

  9. ActionPotential
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    ActionPotential Junior Member

    No I can't. However I am sure there are many who could.
    I made a mistake some time ago on another forum when I opined that spinnakers lift the bow. I was seriously shot down by Dave Culp
    who explained that they appear to lift the bow because they depress the bow less that other sails (mainsails and jibs). What we were talking about was sails arranged (trimmed) to give maximum forward force (efficiency).
    Dave explained that spinnakers could be set up to actually lift the bows but in such a configuration the forward force would be so diminished to make the rig ridiculous.
    In the same discussion we talked about canting rigs (on yachts) and sailboard rigs and concluded that canting rigs are used to bring the rig upright (trimaran heeled 10 degrees, rig canted 10 degrees) to it's most efficient configuration. Similarly an efficient sailboarder will cant the rig to windward to lift his body out of the water and then keep the rig upright for maximum efficiency. Sailboards and monohulls do not use upforce from the rig to help them "plane". In the picture shown the sailboarder is using upforce from his rig, not to help him "plane" but to help him fly and in so doing is giving away most (all?) of the forward drive. this is ok as he is going plenty fast enough already and is into glide mode rather than drive mode.
    When he lands he will revert to drive mode and use his rig at max efficiency again.
     
  10. mike leneman
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    mike leneman Junior Member

    le grand tri

    Well, I like your constuction method.......we use styrene foam in conjunction with thin plywood as well......BUT - I'm afraid you will not like my prediction.
    First, you will not be in the water in February if those pictures are from this year. I don't think you realize how much more work you have in front of you.
    Second, I don't think you will be happy with the ride or the performance.
    Remember, Paul Ricard, et. al, were only marginal successes and few have followed that path.
    BUT: I applaud your energy and efforts.
    Bon chance !
    Mike
     
  11. Doug Lord

    Doug Lord Guest

    lifting spinnakers

    AP, Dave Culp is dead wrong at least on RC spnnakers such as these:
    s50witha1.jpg
    Address:http://www.microsail.com/images/s50witha1.jpg Changed:8:47 PM on Friday, November 24, 2006
    --------
    And I strongly suspect that on several of the skiff classes the spins lift the boat.
    When I develped these models they were the first fully gybable rc production spinnakers and in development we made hundreds of tests to ASSURE that the spin would lift the bow.In fact, the boats can sail in stronger wind dead downwind with the spin up than they can with just the main and jib! The spins are relatively small and flat but add tremendous power to these models; when a gust hits you can physically see the bow lift.
    ----------------
    105 see para 5:
    J/Difference
    Address:http://www.jboats.com/sailingj.htm Changed:12:24 PM on Wednesday, September 20, 2006
    -------------
    505
    "The power in the big spinnaker is incredible and the remarkable thing is it lifts the bow and actually make the boat easier to steer in big seas and big...."
    www.passagen.se/waterat505_has_verve.htm
    -----------------
    Dr.Ian Ward 07 March 1999 (his second letter 3.0 Longitudinal Stability) Spinnaker provides Lift
    Discussion
    Address:http://culnane.navidat.com/dc/sailing/moth/wshpaper/discussion.htm Changed:10:46 AM on Monday, January 30, 2006
     
  12. mike leneman
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    mike leneman Junior Member

    lift from a spinnaker

    The majority of Farrier designed boats that have gone over have done so while sailing downwind with a spinnaker........I would say that over 90% of the "capsizes" have been pitchpoles with spinnakers up. Spinnaker that looked, by the way, very similar to the ones on Doug's link.
    If they provide so much lift, then why did these boats pitchpole? Why didn't there bows come up? They even have pretty big bowsprits, which should help the "upward" angle of the spin.
    Ah, yes, these boats even have planning hulls, which should raise the bow even more.
    Enquiring minds would like to know.
    Mike Leneman
     
  13. ActionPotential
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    ActionPotential Junior Member

    Resolved solution? I thought we had that long ago.
    The resolved solution is that it all depends on your definition of planing.
    If we take Ian's definition of skimming across the top of the water then obviously trimarans can and do plane on the main hull.
    If we take my preferred definition of skimming across the top of the water supported by hydrodynamics only then a tri centre hull can't be planing if some other force is contributing.
    If we take the in between definition of skimming across the top of the water supported by a number of forces, one of which is hydrodynamic, then it gets complicated. How much hydrodynamic is needed to make it planing, 50%?, 10%, 1%. If it's not 'all or nothing' then we must accept that a 'non-planing' shape still qualifies, even if it only contributes 0.0001% of the lifting force.
    Thus I can plane my windward hull on the tip of the daggerboard.
    For me it has to be hydrodynamics only but I am happy with just skimming, I just can't accept the inbetween because I can't see the justification of where you draw the line.
    I will continue to say that my cat hulls do not plane and I will continue to reply when someone says that they were planing their (trimaran) main hull, "sure, you were skimming it across the top of the water".
    The fastest thing I saw last week was Wilparina 2, (Modified Farrier 31 - canting rig - foils in the amas) spinnaker reaching with the main hull clear of the water and the leeward hull partly foil supported. No planing there.
     
  14. Doug Lord

    Doug Lord Guest

    lifting spinnakers

    For those interested in contributing and/or learning more I've restarted the topic under "Sailboats". It's a fascinating topic that deserves some study...
     

  15. RHough
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    RHough Retro Dude

    Cliff's Notes version:

    Dave Culp who has forgotten more about the nature of sails and kites than most of us will ever learn is wrong. My Model boats look to me that the bows lift, so it must be the spinnaker. To support my claim I'll post some advertising and a link to a Swedish site that has nothing to do with boats.

    Anyone convinced?
     
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