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  1. #29
    That's right – you'd think that is a logical explanation. Others think even more simply – namely that shifting the mast foot further forwards will add more rig weight to the nose, weighting it down.

    But what actually happens when you shift the mast foot forwards is you rake the rig back and the boom lowers. That in turn tends to add sailor weight to the board tail so the nose of the board might actually be higher.

    What shifting the mast foot forwards also does is to increase the distance of the rig from the fin, reducing the railing effect (torque load) on the fin. And so people often shift the mast foot forwards on a slalom board to regain control in windy weather – not to 'hold down the nose' but to regain control over the fin. The lowered boom gives you more control over the rig at the same time.
    With the board back in control, you can then trim the board to be more level for better speed.

    I'd say it best not to talk about nose up or nose down as this sidetracks the true causal relationships.
    Last edited by basher; 15th November 2017 at 04:01 PM.
    Now back in the UK.

  2. #30
    Senior Member Radialhead's Avatar
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    Quote Originally Posted by Wing 11 View Post
    Percentage aera of sail below and above the boom could have sideways manner not fore and aft board trim...
    I don't know why you think that. If you're in a powered-up stance, hooked in & leaning back, & somebody tries to pull the top of your mast away from you, & you have the strength to resist yourself from being pulled upright, there has to be a downward (& sidewards) force on the mast foot. The mast will be trying to rotate vertically around the boom. Build yourself a model & try it out.

    Quote Originally Posted by Wing 11 View Post
    But they are also internal force..
    Irrelevant.

  3. #31
    I can see that many people have yet to grasp the concept of internal and external forces.


    Once we are planing in a straight line on a windsurf board all the forces that were important when we started out are now in equilibrium. So the levers are all irrelevant until say a gust hits.

    When planing along in a straight line it's like being towed by a rope connected to a speed boat. The rig power is basically in one direction, pulling our kit along against the drag resistance of the water acting on our board and fin.

    When a gust hits there is then a slight change to this single force, but it's a complex reaction because the mast bends to release excess power whilst the rig tries to translate the extra power into greater speed. Our body shape also responds like a suspension/cushioning unit.


    But the area above the boom in relation to sail area below the boom is not really relevant to this discussion, beyond the control we feel over our rig. A higher boom will probably put our hands more in line with the pull of the sail (centre of effort) but the lower boom is easier to hold on to and to sheet in when in front of us – rather than higher in the air.

    Any change in the turning movement of the sail about the boom that happens when we alter boom height is not really relevant because it's a neutralised force within the mechanics of us moving forwards.



    It would be great if we could have some other views on this complex issue.
    Last edited by basher; 15th November 2017 at 04:38 PM.
    Now back in the UK.

  4. #32
    Senior Member Radialhead's Avatar
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    Quote Originally Posted by Wing 11 View Post
    Main difference in low and high boom is in harness lines angle,low boom more horizontal lines,high boom more vertical lines=you can hang much of your weight on boom and keep much more sail force,also trasnfer much more weight to mast base..
    Nobody's disputing that, but it's not the only difference, & may not be the main difference in every situation.

    Quote Originally Posted by Wing 11 View Post
    horizontal lines,huge weight on board tail and almost nothing MFP on this picture..
    Attachment 15730

    vertical lines,huge weight on maste base,less on board tail..
    Attachment 15731

    (when sail fast on rough hard wind water and sheet out,nose lift up becasue you dont have weight on mast base although you stay with 70% in froont foot strap)
    Again, that isn't the only change that happens when you sheet out. But I get the feeling you've already decided everything that's going on so I'll leave you with your thoughts.

  5. #33
    I would wonder whether if the boom is adjusted upwards, harness lines are left the same length and sailor is well powered there is a tendency to end up with a lot of the power going through the back foot, especially if the sailor has had to pull everything to the back to get hooked in. In this scenario the board could luff/ stall or could end up skittering off the tail and thus be perceived to be riding 'nose high'. With some adjustments they might then get it back under control. The choice for the sailor is whether the higher boom makes a positive difference in terms of early planing/ comfort etc, which will likely be very individual.

    Just trying to make some sense of a very technical thread and going a bit from personal experience, so apologies in advance and no claims to be the oracle on this one!

  6. #34
    Senior Member Gorgesailor's Avatar
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    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".
    no
    Last edited by Gorgesailor; 15th November 2017 at 08:02 PM.

  7. #35
    Senior Member Gorgesailor's Avatar
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    Quote Originally Posted by Wing 11 View Post
    You think on that?

    It is much more easy to hold falling tree(Sail) whit rope 1 then rope 2.
    Rope 1 represent = higher boom instead low boom,seat harness instead waist harness,lean far more out instead upright stance,tall surfer instead short surfer

    Attachment 15732
    Using your own diagram: Yes, you have more leverage with the higher boom, but what is the vector of the force? It is easy to see how the force is exerted upwards in the higher boom scenario vs lower. Also as radialhead pointed out, the mast/boom connection introduces a fulcrum at that point which affect forces at the base of the mast - whether strictly leeward or fore & aft or a combination.

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