Wing mast practice

Discussion in 'Multihulls' started by HASYB, Sep 1, 2012.

  1. teamvmg
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    teamvmg Senior Member

    Blimey Silver... I reckon that I have been fairly well educated in English and I am struggling with this lot.

    Its a wing mast thats he's got not a wing section mast or a wing sail - a wing mast.

    How do you put the shroud attachment 400mm aft of the center of the mast on a 300mm mast?

    Give the fella a chance.........



     
  2. Gary Baigent
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    Gary Baigent Senior Member

    Hielan, maybe you should extend the hounds fitting out to make a beak. say 40-50mm protrusion. It is difficult to tell from this enlargement but the rigging connection looks very close to the mast ... and even though your wing mast is not large in chord or thickness, tight rigging shrouds will be halting correct rotation.
     

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  3. Silver Raven
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    Silver Raven Senior Member

    Gooday 'vmg' Please accept my apologies.

    I knew I'd get it mixed up - for sure. Please let me try again - - from the very front of the mast - up where the hounds take off point is - which should be one central point - to allow the mast to swivel withhout to much restriction - the side-stays should go down to the deck - to attach to the hull structure - where the desired structural loads can be accepted - at that attachment point to the hull - is the point of attachment that I was trying to refer to. Usually people seem to put that point way to far aft & thus interfere with the clean sail flow rotation of the mast & sail - when broad reaching.

    Does that make any 'cents' now ??? sure hope so, don't want to waste anyone's money (ha ha).

    Regret the errror of my English - as an ex-pat Canuck - living in OZ - I've never learned much more than 'OZie-speak'. ciao, james
     
  4. Silver Raven
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    Silver Raven Senior Member

    Gooday Hielan - I'm the one who needs to say 'sorry' - I did not explain myself very well - at all.

    Your mast - sure is a 'wing-mast' & is much bigger than I thought it was & seems very advanced technically. Both the boat & the mast will surely give you much pleasure & go very quickly when you've got it tuned properly. Sure wish I was over to give a hand. I've been playing with multihulls & wing-masts for a few years now.
    Gary's comment about getting the front piviot attachment point a few cm's out the front of the foil section is very correct. I'd forgotten that our wing had the hounds take-off point some 45 to 65 mm out front of the wing mast skin.

    Sure trust - all goes well with your improvements. ciao, james
     
  5. HASYB
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    HASYB Senior Member

    Thanks a lot for all the comments and advice, sure did give even more inspiration to work on the mast and get the boat sailing asap.

    Cheers,
     
  6. teamvmg
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    teamvmg Senior Member

    Why not just cut the back edge off of the mast?
     
  7. Gary Baigent
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    Gary Baigent Senior Member

    Would be too blunt, Teamvmg, spoil airflow, just imo.
    I think Hielan should go ahead and cut the track free and move it to the sharp edge. Also he won't need the pivoting headboard sheave if he does so. Less weight, drag.
     
  8. HASYB
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    HASYB Senior Member

    I'll leave it for now and just do the repairs and go sailing.
    If I cut the back end, which I also considered, it would leave like Gary says a airflow spoiling 8cm wide backside of the mast.
    For this winter I was thinking of building a bridge-like structure on the current track base, which would be about 8-10 cm high, and mount the track on that. Off course trying to comply to some aerodynamic insights.
    Also thinking of extending the nose of the mast, which is a bit blunt, with a 5 cm foam ridge.
    If anyone has any ideas for/about the mods, construction wise or other, please share.
     
  9. Silver Raven
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    Silver Raven Senior Member

    Gooday "HAS" - Yes I do have some (several) ideas to do with your wing-mast.

    We built a very successful wing-mast back in 1965/6 & sailed it for 8 to 10 years. The wing was very light, strong (didn't break) rather big (11.7 mtrs high - 360 mm thick @ 460 mm aft of the leading edge - 1530 mm front to back @ the bottom & 610 x100 mm@ the top. It rated 11.89 sq mtrs pf wing-mast sail area in front of 9.94 sq mtrs of fully battened soft sail of total surface area out of 21.83 which is the area of a 'B' class catamaran like the Tornado. I have also been involved in several 'C' class wing masts over many years.

    1/ If the wing-mast can rotate 140 degrees smoothly & the soft sail can rotate independently another 20 to 25 degrees - then you do not have a problem.

    2/ Can you ease out the 'track area only where the head-board fits - up the top of the mast ???

    3/ Please think verry carefully before making the fornt of the mast any less blunt ! ! ! Gary & I have differing views of this - that's O.K. but think very carefully before going any where near as pointed at the AC 45's - cause they are going much faster & can thus afford a 'finner' leading edge foil - - I would not do that ! !

    The 'trailing edge' of the wing must join the soft sail - without any gap or bump of any kind. The 'break-away' of laminar flow starts from the front of a hard surface foil & the 'break-away ' of the laminar flow starts from the back of a soft foil. Thus it is vital that there is no gap or bump or hollow in the area of the joining-up of the 2 foils. There must be a smooth transition not a step or you will de-power the effective sail area by causing early 'break-away' of liminar flow on the leeward side of the whole sail area.

    4/ Why do you need to 'build a bridge' structure ??? - doesn't the luff-rope fit into the grove hidden inside the back outer skin of the wing mast ???

    %/ Before any alterations - I suggest you do some research into NASA foils - as I think you might be somewhat surprised as to what is aerodynamic & what is not & at what speed some foils work & some don't.

    I wish you great success but do progress carefully. wishing you good fortune, ciao, james.
     
  10. tspeer
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    tspeer Senior Member

    I used to think the lee side should have a smooth, unbroken contour, too. But the more I've looked at the aerodynamics of wingmast/sail combinations, the more I'm thinking the mast trim should be somewhat different.

    If you trim the mast so the lee side is a smooth contour, then it's highly likely there will be a large separation bubble on the windward side, with the flow separating from the mast and reattaching some distance back on the sail. From the CFD simulations I've run, there is less drag if the mast is trimmed to create a small separation bubble on both the windward and leeward sides. This means there will be a concave kink in the leeward side at the mast/sail junction.

    I now think the best way to trim the mast is to position the stagnation point just to windward of the leading edge. This can be seen by putting a dense row of short telltales around the mast. The stagnation point will be at the dividing point, where the telltales point in opposite directions. An alternate method is to mount a small dinghy wind vane on the mast centerline, with the tail just barely clearing the mast. The tail will go to the leeward side and stay there when the stagnation point is on the windward side. If the tail is mostly to leeward but flicking occasionally to windward, then you've got the mast trim about right.

    Frank Bethwaite found that it was good to have a blunt, flat base to a wingmast, which you can see in his section for the Tasar dinghy. I think it depends on the thickness ratio of the mast. From the maximum thickness, there's a limit to the angle at which the sides of the mast can be brought together without the flow separating. If you don't have enough mast chord to bring the sides all the way together at that angle, it's better to just truncate the mast at the design chord with a flat base rather than to increase the curvature to achieve the closure at the design chord. If the angle is too steep, the flow is going to separate anyway, so you haven't reduced the wake of the mast by making it more curved. It's better to keep the flow attached all the way to the backward facing staep and accept the separation bubbles that will lie behind it. The angle will depend on the size of the mast and the speed range for which you want to design it, so it's not possible to name a single value for it.

    (BTW, "laminar flow" and "attached flow" mean two different things, as do "turbulent flow" and "separated flow". I think you meant the flow should be attached as it flows from the mast to the sail. The transition between laminar flow and turbulent flow is likely to have occurred earlier on the mast, although it could still be laminar at the point where it separates to form the windward separation bubble. The flow in the boundary layer will definitely be turbulent but attached where the telltales are laying flat on the sail.)
     
  11. Silver Raven
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    Silver Raven Senior Member

    Gooday Tom & thank you so much. My respect to/for you, Steve Clark, that 'Canuck' - blunted & a few others - is - of the greatest magnitude.

    What with my 7 out of 10 - dyslexia - I more times than I'd wish - get my terms & phrases - totally - out of sync - I regret that very much - it is my short coming. I can't type-talk the talk - however I can & have - drawn the shapes - chosen the production methods & materials - built the wing-masts - sailed them (& into 1st place for several years) - so I'm still hangin-in-here & trying to learn - so I can go out there & do it all over again. Thanks for you comments & guidance - so very much appreciated, ciao, james
     
  12. teamvmg
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    teamvmg Senior Member

    Tom
    My stupid sailing head is struggling with that

    What you are saying is that a wing mast should always be trimmed for minimum drag. You would trim it the same on a day when the boat is over-powered to a day when you are looking for maximum power - there is no powered-up setting?
    Seems like a waste of time having one!
     
  13. Gary Baigent
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    Gary Baigent Senior Member

    Depends on the chord and thickness. Obviously the longer chord is going to make a less disturbed air flow (on the windward side) from wing mast to sail, especially if the thickness ratio is down. The tricky part is building a fine wing mast that is strong and does not flex too much - and also is not too large in chord that excess power is always there when moored.
    All I know from sailing my own boats is that when you over rotate the mast (and the leeward flow is fair onto main) the boat accelerates like a Ducati.
    Sure, in overpowering conditions, you can reduce the rotation ... make the bubble to windward and to leeward equal, that does reduce power - but also increases drag. Better to reef.
     
  14. teamvmg
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    teamvmg Senior Member

    Yes, I know. My point was, that if you wanted to de-power a wing mast, you would set it as TS has described. Yes?
     

  15. redreuben
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    redreuben redreuben

    About 20 years ago a workmate built himself an experimental mast that he put on an Australian 18ft skiff hull.
    It was aluminium and D shaped although the leading edge was a bit more cone shaped.
    It was tapered and at the base the chord and thickness would have been around 150mm, probably a bit longer in the chord.
    The flat of the D was aft and had a sail track on either side so it hoisted two lightweight mains the clews of which were joined by a rope with a pulley in the centre leading to an outhaul on a boom.
    So sail shape was primarily controlled by mast rotation (with spanner) and outhaul, I don't remember if cunninghams were fitted or not.
    That thing had sail shape I have never seen bettered in a wing/soft sail set up and went to weather like a train, it was easy to adjust and sail and was easy to build, with a carbon stick it would have been even better !
    I'd be interested to hear the comments of the knowledgeable !
     
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