Can somebody explain to me in simple terms the physics or hydrodynamics of pumping the sail and the board? I don't need to know how to do it, but WHY it creates acceleration of the board. Please note that I am not an engineer . I don't need complicated formulas,only the concept.

Another question I might ask is whether the floatation of the board (and the planing) is better in deeper water than in shallow water.
I sail in freshwater with a 180 lts board. Later the water level has come down to less than 2 ft near the launching site and I have been experiencing some difficulties in starting out.I have to walk the board for about 200 yds until I reach deeper water, which is quite annoying.

Thank you

Francone

Francone

Nick0 explanation is probably clearer, but in a bit more detail

Imagine a windsurfing slogging along slowly.
1. Sailor pumps the sail, pulling it towards him/her self.
2. The sail now has to push (an additional force) against the wind. (think of a swimmer taking a stroke through water)
3. newtons laws, state that for every action there is an equal and opposite reaction
4. The opposite (reactionary) force (the additional force/effort you feel in your arms while pumping) pushes the board/sailor forward. (as the bouyancy/shape and centre of weight for the board&sailor will naturally push the board upwards when accellerated forward)
5. Part of this reactionary force will accelerate the board forward and upwards, thus hopefully allowing the board enough acceleration to start planning.
6. Once planning it requires less energy to stay on the plane, then it originally was to get on the plan.

As to the shallow / deep water planning. There is no difference except maybe in very very shallow water (inches). I suspect what you are noticing is there is less wind at the shoreline then in the deeper water. This is due to the wind slowing down as it rises over the land and the greater friction between wind over land than wind over water. The more onshore the breaze the greater the effect. This effect does create a "lighter" slower windspeed area out into the water. If this doesnt make sense you could think of it as a merging lane from 2 to 1 lanes, everyone slows down as they try and merge, and force the cars behind to slow as well. But the cars 200 m back up the road are still moving at normal speed untill they get to the merge.

I hope this makes sense

cheers

beeblebrox

I know Fancone can do it and isn't after tips, so on a tangent...I find some beginners have trouble with pumping and flap the sail around wildly with no effect. I call it pumping the fin or loading and unloading the fin and suddenly they find it much easier. All the above applies but there is also a lot to do with fin lift generation as well as apparent wind generation

As far as I can tell it's more about climbing the bow wave than anything else -- a good pump accelerates you up to speed, by which time you're light on your feet, falling down for your next pump, so the board doesn't have as much weight to resist it climbing the bow wave.

This explains why just bouncing the board can have a similar effect.

I've only recently learnt to pump properly, if anyone's having as much trouble as I was then the thing to remember is that it's all in the bum! If you keep the sail steady, and do your best approximation of a gigolo, you'll be off and planing in no time

pushing against the fin.... in out in out in out
plus lifting board up down up down up down

hip motion looks a lot like rootin

need a vid to explain?

I'm not sure if my technique's right...especially after the 'rootin' comment!

The increased air flow definitely makes a diff, but I've found that by leaning back slightly when pumping, you're taking your weight off the board, which is (as mentioned also) equivalent to jumping, and as we know, reducing your weight = planing sooner (as he puts down 3 big macs).

This makes a huge difference, especially with modern (short/wide) boards which tend to 'pop' to the plane, and are either planing, or slogging.

If you're just off planing speed in marginal conditions, pumping the sail can turn a disastrous slogging nightmare into a top sesh!

I'd like to give pumping a go, it sounds pretty good. A movie or series of pictures showing how one pumps one's body would probably save much frustration.

lol that is not sail pumping ... he is trying to balence as he in knee deep water on this board ... sail pumping is a hole body sail and board movement

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after he comes out of his first jybe ... thats pumping ur sail .. on a wave boars with a 4msail its a lot faster ... watch as he gets further away the uper leach flopping back and forwards

just youtube .. light wind formula sailing and u will find a suitable video

birds pump their wings to fly.

Mark _australia said...

hip motion looks a lot like rootin

need a vid to explain?

I was really hoping that Mark would dig into his collection of vids to explain...

Instead I found this:

It seems from Nebbians video that it is as much about 'feeling' when to stop pumping, and making a smooth transition into ya straps without letting the board fall back off the plane. I often 'tell' myself when I'm sailing that i've gotta take my opportunity to plane ,coz sometimes you miss it and end up shlogging for the whole run, spewin' about that lost chance to get going, whether it be that little wave run or an extra knot or two. Sometimes in marginal conditions you have to really concentrate to get going, then relax when you're off and running!

I'm not sure on (2), but by jumping on the board, you're doing 2 things, getting air to pass under it, which breaks the drag (friction) caused by the water, hence allowing to 'pop' the board onto the plane...also it reduces your weight for a split second, which in most cases when you're just off planing will allow the board to lift also. Probably not scientific responses, but physics was never my strongest subject...I'm more a "if it works, then that's what you do" guy.

Maybe the pressure on the fin comment means that by putting pressure laterally, you're reducing the downward pressure (weight), and allowing lift??? To achieve this, you'd have to be committed to your harness, or boom, and have the sail leaning back, which is how I find is the best technique for pumping the sail anyways.