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  1. #22
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    In the days before proper boom clamps, I landed a jump and the boom slid to the bottom of the cut-out. By the time I got back to the beach to move it up again, my front thigh was burning from the pressure on my front leg. It's more front foot pressure than mast foot pressure IMO that the boom height affects.

    If I'm jumping and the boom is at the right height, the board will want to level off at the top of the jump. If the boom is higher, the board will want to be tail down. If the boom is lower, the nose will tend to want to go down. Other things affect the board position too, but that is just looking at the boom position in isolation.

  2. #23
    Senior Member Radialhead's Avatar
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    Quote Originally Posted by boards_ronnie View Post
    If I'm jumping and the boom is at the right height, the board will want to level off at the top of the jump. If the boom is higher, the board will want to be tail down. If the boom is lower, the nose will tend to want to go down.
    Which backs up the fulcrum theory. It's like a plane with one wing longer than the other. The long wing will generate more lift & rise up, lifting anything that's attached to its end. High boom = longer wing below the boom = lift on the mast foot, raising the nose.

  3. #24
    Quote Originally Posted by Radialhead View Post
    I think you're wrong there. The wind generates an outward/forward force above the boom, which must have an opposing inward/downward force below the boom as the boom acts as a fulcrum. There is of course also an outward/forward force on the sail below the boom from the wind.
    ........

    I think you are mixing up internal and external forces.
    Now back in the UK.

  4. #25
    Senior Member Radialhead's Avatar
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    Not at all, but as you're never wrong, I'm not going to waste my time explaining what's wrong with your statement.

  5. #26
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    Quote Originally Posted by Wing 11 View Post
    So you mean that front foot is most responsible element for stay nose down?
    What is with mast foot pressure(MFP) in your description or you think this is just virtual termin that do not really exisit, like some people belive,because MFP is also internal force?
    pressure directed on the board is a result of counteracting the force exerted by the sail which is transmitted through the harness lines and riders body to the only other point of contact between rider and board.....their feet.
    I think there is some downward pressure on the mastfoot created by the rig forces. The main force is to leeward and of course both the mast foot and the riders connection to the boom resist that force. Whereas at the boom the leeward force is resisted by the harness line through to the sailors body, at the mast foot the force is converted into one trying to tip the board onto its leeward rail.....and a proportion of that will in effect be downward. It is the sailors position on the opposite rail that resists the majority of that force. Adding it all up I think any force directed downward by the rig ( mft) is marginal compared to the main forces at play. That minor element of mft will also vary depending on the angle of the rig rail to rail.
    I'm not sure anyone can fully define all the forces at play on a windsurfing set up! Better maybe to just discover how to use the various tuning/trim elements available.

  6. #27
    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.
    Last edited by basher; 15th November 2017 at 02:03 PM.
    Now back in the UK.

  7. #28
    Quote Originally Posted by Wing 11 View Post
    This is the main cause for confusion,because higher boom gives more mast foot pressure (in theory) but Pro wsurfer say "put boom down if you want nose down".
    Yes, I've already tried to explain that, back on page four. It's a wording thing.

    We used to have a similar issue when talking about mast foot position – people still say 'put the mast foot forwards to hold the nose down' when what actually happens when you move the mast foot forward is not best described that way.

    Similarly, some people think they will go upwind better if they put the mast foot forward – when in fact the opposite is often the case.
    Last edited by basher; 15th November 2017 at 03:48 PM.
    Now back in the UK.

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