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  1. #78
    Senior Member Graemef's Avatar
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    The only confusing information here is you spouting nonesense.

    Just because you ' don't recognise any of the 'change in leverage' discussion others are having here.' simply indicates a lack of experience of a sailor who's spent his entire time just sailing for fun, without the requirement to plane early or sail over powered, because anyone who has knows the importance of leverage over the rig and the need to adjust boom height according to conditions.

    So your input is entirely confusing, why keep on doing it, you obviously don't understand?

  2. #79
    My 'input' is not confusing at all, you just disagree with it – although this is a complex subject because we all sail different gear.

    Most people sailing shortboards will have found a boom height they like and they then stick to that. Slalom sailors – on bigger sails – might alter their boom height as tuning thing, just as they might shift their mast foot on the board.

    But once you are on a shortboard with the rig set near the foot straps for an upright stance, such as a wave board, small freeride board, or freestyle board, the boom height preferred will be based on your physical height first and very little else. Shifting it up or down the mast an inch or two then has very little effect in terms of leverage over the rig.

    Then again, I've made it clear I'm generally talking about people using small rigs. If I want more power or more 'leverage' from my sail then I tighten the leach a bit by easing the downhaul.

    So this means we think differently about our rigs according to what kit we are sailing.
    Now back in the UK.

  3. #80
    Senior Member Graemef's Avatar
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    Quote Originally Posted by Wing 11 View Post
    links about MFP:

    http://www.guycribb.com/userfiles/documents/downforce.pdf


    http://pritchardwindsurfing.com/how-...ur-windsurfer/

    http://www.shawnacropas.com/tip2/


    quote text from first and last link:
    Downforce is as vital to your traction control in windsurfing as it is to Formula Oneracing cars. Its the downward pressure that keeps the board flat on the water, even whenyoure stood near the tail. The best way to create Downforce is by pulling down into theboom, taking some of your weight off your feet and pushing it down onto the mast footinstead. The old school called this Mast Foot Pressure or MFP

    "We want to use our weight rather than the strength of our arms to counteract the power of the wind in the sail and keep the nose of the board down with mast foot pressure (the result of your weight transferring from the boom putting pressure down through the mast so you dont sink the back of the board)."



    So all this instructors and profi wsurfers are idiots???????

    No they are reinforcing what we've been telling you, that there is little to no 'natural' mastfoot pressure when you need it, unless you bear off or sail down wind, all the rest of the time it has to be manually induced by stance it's why the top half of the body of pro racers is generally further forward than the bottom, to keep maximum waterline length up wind, or to ensure the board doesn't lift off when racing or to keep weight off the fin and keep the nose down. The height at which you set the boom will depend on the height of the sailor and his requirement to keep the nose down, so some might bring the boom back, but others won't
    Last edited by Graemef; 20th November 2017 at 03:16 PM.

  4. #81
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    Quote Originally Posted by basher View Post
    If anyone is now confused by this thread that is understandable.

    There is seemingly opposite advice being given here, by people who are convinced they are right.

    I wonder if the differences are based on the kit normally sailed?the op posed his question on the basis that he is sailing a NP Evo sail and Isonic Board.....slalom gear, which whilst more sensitive and radical has all of the same type of components as freeride, freerace and even long boards. Not a lot of point confusing the issue with multi fin float and ride boards I reckon!


    What I do know is that for the small sails and boards I use, I'm usually sailing along with a downward load from my mast foot and I can increase this by leaning forwards whilst hanging off the boom and driving the board via my harness lines.wrong....your mastfoot cannot provide a downward load, it is merely the connection to the board. The load has to come from some component connected to it..ie the sail or the riders connection to the boom. The sail is designed to provide lift and leeward pressure not downward pressure, so that leaves the boom connection. You may think yu are applying pressure down through the boom but if you are planing ..which is when controlling nose lift/trim is an issue....the shox video clearly shows you are not
    In my world, one reason for a higher boom is for jumping, and there's an argument for using a low boom when DTL wave riding.not relevant in terms of controlling nose lift/trim other than the fact that a higher boom releases some pressure on the nose and therefore makes it easier to chop hop or jump

    A higher boom might help me plane earlier by loading the mast foot more and reducing my body weight on the tail of the board but I personally don't like a high boom in the first place for other reasons, mostly to do with sailing comfort.yes it does but not because it increases the non existant mft but because it helps take weight off your front foot which in turn help the nose to overtake the bow wave

    Having a lower boom gives my more control over the rig because it's more in front of me, and it gives a good line of pull (outward) on the harness lines, and this has proven to be a fast stance for me.

    For sure, most people will set boom height vaguely in relation to their physical height and for me that usually means the middle to lower part of any boom cutaway.
    I don't recognise any of the 'change in leverage' discussion others are having here.you will not recognise anything if you continue to think in terms of downward pressure on the mast foot whilst planing

    I also know that the small fins I use have little or no effect on board trim and I control how level the board is by shifting my body weight, and that alone is what 'lowers the nose'.yes you can shift the weight distribution on your feet by leaning forward or back but if you think "that alone" is how you trim the board then you are missing out on other trim option available to you that do the same....mast foot position/boom height/sail trim
    Early planing is actually down to me too, regardless of boom height. If you are a passive sailor then planing happens when you gain enough forward speed to overtake your bow wave. The active sailor gets the board planing earlier by getting the board unstuck and onto the water before there is much of a bow wave and so it's handy too know how to work the downward loads on your board, as well as how to pump a rig, regardless of boom height.which is a statement of the obvious but made needlessly harder to do if you have poor board trim in the first place

    I do understand that those on bigger, stickier kit, might find themselves pumping the fin sidewaysmmm....try pushing against a slalom fin! I'm afraid this is hopelessly wrong. A slalom board uses a relatively small, very stiff carbon fin with a very shallow profile. It provides little or no grip until speed is achieved. Even on freeride/freerace boards with somewhat less radical fins, if they are the newer shorter and wider type of design...which most now are....you do not get planning by pushing on the fin....that is old school! whereas I'm working downwards against the buoyancy of my board.no difference there then If the wind is marginal, I go for more buoyancy under my feet before I change to a bigger sail size.or more width...which is more normal these days

    I wonder if we sail our modern kit differently from the way we used our earlier gear? In the old days, you'd hear talk of people sailing along with their rigs canted over to windward and the theory used to be that that was how a windsurfer planed fast compared to other sailing craft where the rigs are more commonly heeled to leeward.
    I'm pretty sure I sail with my mast upright and with my boom positioned so that I'm at arms length from the rig with my bum nowhere near the water. And I guess it's differences like these that might determine whether your mast foot is in tension or compression on the board.No. The most efficient position for the rig is upright ( rail to rail) ..not pulled over towards the rider. That applies to all slalom, freeride, freerace and race boards. Arms length from the rig is standard for all types of board. If planing the mast foot is in tension regardless.

    Does mast foot pressure exist?when planing? No Yes it does. Does the U/J take other loads at times, yes it does.of course, but what we are supposed to be discussing here is degree of nose lift as affected by boom height!

    Planing is by the way spelt with two 'Ns' not three at it's short for aqua-planing. Planning is something I do at the beginning of each week, organising my time based on the wind forecast and work load.a double "n" is the default spelling on this site for whatever reason..it auto changes the correct spelling...sometimes I really cannot be bothered going back to remove one of the "n"s
    Hopefully the comments in bold help to clarify things!!

  5. #82
    Quote Originally Posted by mikerb View Post
    Hopefully the comments in bold help to clarify things!!

    They have clarified that you don't know what you are talking about.

    We agree that a modern board is sailed with the rig upright. It's then difficult for you to explain how the windsurf rig can have an upward component in the lift which then puts the mast foot in tension.

    All types of windsurfing kit are allowed in this discussion and wave boards were talked about from the start, not least in the TWS video linked to and then discussed.


    I think there are times that the mast foot is in tension. I was also the one at the start staying how body weight is used to apply increased mast foot pressure.

    We are only connected to our boards via three points: our two feet and the mast foot. All three are inevitably in compression a lot of the time.
    Last edited by basher; 20th November 2017 at 08:49 PM.
    Now back in the UK.

  6. #83
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    Quote Originally Posted by basher View Post

    We agree that a modern board is sailed with the rig upright. It's then difficult for you to explain how the windsurf rig can have an upward component in the lift which then puts the mast foot in tension.
    Not sure I understand the grammar! I do not find it difficult. The rig creates lift...that is what it is designed to do.

  7. #84
    Quote Originally Posted by basher View Post
    Let's go back to basics here – perhaps for those who are new to windsurfing.
    I'll also try and explain about external and internal forces. There are lots of levers and fulcrums within the windsurf rig, but I'd suggest these become irrelevant once we are planing along.


    So we should talk first about getting going on a windsurfer, then about planing along, then about what different boom height does.

    1) When you first stand on a windsurf board your body weight acts through your legs to the board and as you uphaul the sail that adds to that weight. The board's float takes that load and so you need to stand in the middle of the board to keep it level. With the rig out of the water, the rig weight acts downwards through the mast foot.
    Once you sheet in with the sail, the power of the rig comes into play more than its dead weight, and that power or pull acts through your two feet and via the mast foot onto the board. Sheeting in allows you to stand back on the board.
    The initial pull of the sail is from above the boom and acts like a lever, so if you sheet in too fast you catapult forwards.
    So we edge backwards on the board to keep it level as we sheet in. We also lean backwards against the sideways load from the rig.

    2) You then get the board up to speed, planing over the water – and pumping the rig a bit helps unweight your feet so the board becomes unstuck, and a relatively high boom helps this as you are sort of doing chin ups as you pump. But even with a low boom, you can pull downwards as you pump the sail, to help unload your feet to get the board unstuck and onto the water.

    3) Once planing, the forces are more in equilibrium, and the rig is driving you along with most of the leverage forces balancing themselves out (as internal forces). The sideways load of the rig is balanced against the lift from the fin and planing rails so that too is neutralised as an internal force. The remaining drive is like a rope attached to the mast pulling you forwards. The resultant (external) load is connected to your board via the mast foot, and through your arms to each leg and on to the board via your feet.
    So these are the three points of connectivity for what we can think of as a single external force: We feel the rig load via our arms and harness line but the single force connects to your board via your two feet and via the mast foot.

    4) Boom height, mast foot position, and footstrap positions then control your sailing stance. Your stance determines how well you drive the board and control the rig. Where you stand on the board determines the board trim but you can lean forwards or back within the footstrap positions you have chosen.


    5) With footstrap positions fixed and a mast foot position chosen, you can still vary the relative load on each foot, not just by shifting your weight but with the rig load as it acts through your feet.
    The boom height can be changed and the higher setting tends to put more rig load through the mast foot and less through your feet. Some people will also tell you that changing boom height affects which leg – front or back – has more load. But in practice the load on each foot is also affected by the way the sail is rigged and on harness line positions. (And it gets complicated here, because a change of boom height can also affect the setting of the sail which may require outhaul adjustment.) But you can set your harness lines further back to get more load on your front leg, and set them further forwards to get more rig load on your back foot.



    With these basics in mind you can then fine tune your board – and your sailing stance – knowing what changes have what effect.
    But the key thing with boom height seems to be to use a high boom for early planing and a low boom for strong wind control.

    You will sail fastest if the board is level and all too often we see beginners plowing along with the board nose in the air. Boom height doesn't really help that beginner problem because it's really about losing your fear of catapulting and standing further forwards, perhaps with the front foot strap set nearer the mast foot and with the mast foot itself set further back – usually in the centre of the track.
    In slalom boards, you might also change board trim with a change of fin, and often the rake (angle) of the leading edge of the fin has a say in how level the board planes.

    That was my post back on page six of this thread.
    With this analysis in mind, it's well worth watching the PWA live feed from New Caledonia this week, either live or on the replay. We get several shots of the slalom boys and girls sailing along at speed and then they go into transitions at each mark.
    With slalom gear used in a downwind slalom you get a lot of mast rake and it's arguable that the mast rake gives a bit of upward lift from the sail as well as forward drive. The rake of the rig also means a lot of the drive is transferred to the board via the sailors feet so, in a straight line, you can argue that mast foot pressure is reduced.
    But mast foot pressure never goes away and is more in view during the acceleration process. It's then very much in view at the marks where the board nose comes up as the sail is released for the gybe and the nose then goes down again very noticeably as the sailor sheets in on the next tack.


    It's then worth watching the side view of the speeding slalom sailor once he has reached top speed with the sail forces in equilibrium.
    What we see first is the basic movement of the board speeding in a straight line.
    The hydrodynamic lift from the hull works against the downward pressure of the rig and sailor weight – equalised. The sideways loads of the rig are similarly equalised against the lift from the fin and outward spray from the board rail. The sailor is also outboard, using his or her weight against the sideways leverage loads of the sail. The sailor also applies downward weight to the board rail to neutralise the torque lift or 'railing effect' from the fin. And so on.
    These are all the equalised or internal forces, with the main story being about the board speeding along in a straight line. What we see is the resolved drive of the rig pushing (or pulling?) the board forwards, with that single force giving acceleration to the combined mass of the board, sailor and rig, whilst working against the drag from the hull and fin and windage drag as it comes off the sail.
    Within that linear movement we see subtle other forces at play as the board rides through or over chop. The planing (flying) hull rides on a short section of tail and the side-on view shows us how the raked rig aligns the centre of effort over the centre of lateral resistance at the board tail and over the fin. The sailor himself is also more-or-less in line with that C of E over C of LR.
    The subtle deviations within this straight-line set-up are now seen as the board and rig oscillate fore-and-aft to compensate for the ride over chop. The board appears to pivot about the fin, with the nose of the board moving up and down ever-so-slightly. The head of the sail should also be releasing at the leech in harmony with the ride. (And, for those still interested in mast foot pressure, I would suggest the amount of MFP increases and decreases as the board travels over chop.)

    I mentioned earlier how forces applied can be different for different types of gear – and obviously at the other extreme of longboard sailing, there will often be more board in the water. On freeride and wave gear we also plane at half the speed of these slalom guys and we may not ride the board off the fin at all, using the rails more. Generally a wave board will have a relatively longer length of hull in the water when planing, and a side-on view would show the rig more upright (with less mast rake) and with the sailor standing relatively further forwards on the board.


    This is maybe interesting stuff for the armchair sailor, but windsurfing is still best when done on the water.
    Not sure how many will bother to read all the above, but please don't quote me back the one paragraph you have read, out of context.
    Last edited by basher; 21st November 2017 at 06:24 PM.
    Now back in the UK.

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