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  1. #15
    Senior Member
    Join Date
    Nov 2009
    Raising the boom may well result in the board riding more nose high but ( most especially on a slalom board) that would depend on a number of other aspects of board and sail tuning..and cannot be used in isolation of those.
    On most slalom boards, part of achieving an effective trim is to equalise pressure on both feet. Due to very outboard strap positions that foot pressure pushes a gainst the rail but also partly down through the board. Lifting the boom whilst leaving other tuning elements as they were is likely to take some pressure off the front foot, especially across the wind and upwind. That will give less control over the nose of the board. Lowering the boom will likely have the opposite effect. Similarly moving the mastfoot back slightly will make any front foot pressure proportionately less in terms of controlling the nose.....even more so if the boom is kept at the same height. The degree of fin rake also impacts on how the board rides once fully powered, as does the amount of downhaul used......and of course the position of the front strap in relation to the mastfoot position.

    I said initially...especially on slalom boards.........because they typically have short planning flats. Freerace and freeride board typically have longer planning flats to make them a lot less sensitive to trim setting, more progressive in terms of acceleration, and more stable once planning. The same principles apply however but with a lot less sensitivity.

    I have limited experience of boards with tail rocker and/or continuous rocker since they are designed primarily to maximise manoeuvrability rather than planning performance..........I would suspect once having found a comfortable set of strap positions and mast foot position etc to suit your stance and the conditions being used in, there is less scope for change.

  2. #16
    Senior Member
    Join Date
    Nov 2009
    ps..........its fairly easy to determine when too little pressure is on the front foot on a slalom board..........the front foot will not stay in the strap!

  3. #17
    Quote Originally Posted by Wing 11 View Post
    Sebastian Kornum words ; " want to keep nose down,you just put boom down"

    10: 34min

    Listen to the whole NP video here. There's a lot of good advice from both sailors.

    Sebastian actually talks about adjusting boom height as an emergency thing for regaining control – and what does that mean here?
    When out of control the fin is dominating the board and you might be tail-walking rather than speeding forwards with the board level. But it's actually the rig that is causing the problem here (as that's what he's taking about in this video).

    If lowering the boom gives you more control over the rig, then that helps you gain the calm to drive the board more efficiently, weighting your front foot more so that the board levels, with a lower nose.
    That's not quite the same thing as saying a lower boom will lower the nose.

    Both sailors agree to lower the boom in windy weather to regain control.

    Once in control, you can load the front or back foot as required, and that is what determines fore-and-aft board trim.

    I like the Peter Bijl video as well.
    Last edited by basher; 15th November 2017 at 12:03 AM.
    Now back in the UK.

  4. #18
    Senior Member Gorgesailor's Avatar
    Join Date
    Dec 2009
    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?
    I am sorry for my sarcastic nature, but I always think its funny when engineering minds try to oversimplify what is a very complex system. When the sense of logic is over riding what you can feel with your own hands(&feet) or for that matter what a Pro sailor tells you. The Pro is obviously correct, it is just a matter of understanding why - & what he is saying. It could be he is just explaining it badly. It makes sense to me if you break it down into individual factors: First it is easy to see that raising your boom will take some weight off your feet as the C.O.E is then higher. It is a bit more difficult to factor in the mast base pressure. I try imagining that the base was disconnected & you are still holding the boom. What would be the force acting on the base then? What about with the boom higher? Lower? Obviously the boom/mast connection is also a fulcrum so this must affect the force at the base.

    Of course there are many other factors at play here but you get the picture?

  5. #19
    Senior Member Radialhead's Avatar
    Join Date
    Sep 2012
    Quote Originally Posted by Wing 11 View Post
    I agree with you,sail percentage area below and above the boom have nothing with this.
    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.

    As you move the boom down, the inward/downward force below the fulcrum increases, whilst the outward/forward force decreases. You only need a small change to tip the balance either way.

    It might help to visualise it if you use extreme examples. e.g. with a ridiculously tall rider with the boom at the top of the mast, all of the force on the sail will be outward/forward as there's no longer a fulcrum to transfer any of it in the opposite direction.

  6. #20
    Senior Member lostboy's Avatar
    Join Date
    Oct 2009
    This is hilarious. Mast foot pressure? Is that still going? A basic knowledge of physics tells you that there's no such thing.
    Got an opinion? Great. Guess what, so's everyone else!

  7. #21
    Senior Member
    Join Date
    Nov 2014
    Location, Location
    Quote Originally Posted by rod View Post
    High boom takes weight of the board and helps with early planing in light winds. In stronger winds a lower boom helps you get lower and more weight over the board giving more control.

    People wave ride ride well with either set up. (In the PWA final there were a variety of boom heights extensively commented on).
    I think this is pretty much right. I'm not so sure I'd say a lower boom helps you get more weight over the board but it allows you to get your weight out further and gives you more position options and whatever it is experience tells me it gives more control.

    Windsurfing seems to be an activity where the best practitioners aren't necessarily the best theorists.

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