Lee-Bow..... Windsurfers...etc (Dons tin hat)

Originally posted by 423zero I find it difficult to envisage a vessel in middle of a pack getting a lift from current, but not others around ?

No, I agree, that's unlikely to happen, gains by variance occur generally at the outer edges of a given fleet in a given tidal scenario. Where for example the tide bends across a course or that the tide may be stronger in one area than another and of course fundamentally the sort of gains I'm talking about only occurr when there's a dearth of pressure from the main power source (the sails) and so extra energy is sought from that provided by the current flow that might not be possible on other areas of the course. (We often have a classic scenario with a side on wind and adverse current where generally it pays to hug the coast, but on occasion depending how far out the mark is set and the offshore wind angle on the lay line, it's possible to gain advantage by heading out to sea into the tide far enough to get the flow onto the lee bow then the result can be quite dramatic.)

Or perhaps in the case of the OPs son the other competitors are unaware of the technique required to utilise that extra power.

Which brings me to something else that could be relevant, the gybing centreboard, another subject of controversy because it seems to suggest something similarly 'mythical' that sends all the maths heads scurrying for their slide rules (Calculators these days) and running aorund waving their hands in the air and screaming foul.

Edited by iGRF - 24 Sep 19 at 8:40am

Originally posted by Hitcher . You are correct. It is unlikely (impossible) to happen.

Improbable, unlikely, but not impossible. Or are you suggesting the OP simply lied about the 'effect' his son discovered whilst sailing with a group of other youngsters on sailboards in adverse current, that precipitated this particular discussion?

Edited by iGRF - 24 Sep 19 at 10:44am

Trouble is that sailing today page you reference isn't that clever either. Leeway in the way its described isn't really a thing. What sailors have traditionally called leeway is simply the angle of attack the hull must take up in order to produce the required lift to balance the lift from the sails. If the keel/centreboard lift can be decoupled from the hull centreline (trim tabs, gybing centreboards etc) then the centreline of the boat may be on the line of travel, but the lift required to balance the rig is the same.

The traditional lee bow myth was I suppose, very roughly that the difference between having the tidal stream half a degree off the leeward bow and half a degree off the windward bow was significant and radically greater than the difference between having the tidal stream half a degree off the leeward bow and a degree and a half off the leeward bow.

I've come to wonder, recently, how many people can really tell whether the tidal stream is half a degree off the windward bow or half a degree off the leeward bow. Of course when its ten degrees each way its usually obvious, at least if you have fixed objects like marks, trees or navigation aids to reference.

The thing that article and I think you are all missing, is that we are not actaully racing over the ground, we are racing over the tide wind interface so the sort of maths you're trying for do not apply in small area tactical short course situations, I don't know who Mark Rushall is, never heard of him, so wont be wasting 20 quid to find out, but if he's basing his theory on articles like that, heaven help you all if ever we were to meet in a tidal situation and there were money riding on it.

So shall we tell the young windsurfer he can't do that because some 'maths head' says it's breaking the laws of physics?

From what I know of Langstone harbour mouth the chances of any three craft in close proximity being in the same current are minimal!