LEE BOW EFFECT

Sailing the tack that gets you to the mark quickest works for me, the rest is academic - thanks for that insight Jim

Originally posted by Ian29937 Do gybing boards work?  I used to sail fireballs which allowed them at the time.  They were only used by a few people and then only in some very specific circumstances  (e.g. flat water, medium breeze when the height gain exceded the extra drag and speed loss)   This sounds like a whole new topic

Dude - Great post.  It sums up the issue for me.  There are broadly 3 camps:

 

1.  The believers who have "experienced" lee bow effect, or been told about it and just accept it.

2.  The unbelievers.  I'll explain why below.

3.  The technical believers - GRF's post nearly put me back in that camp and might yet when I go and get my copy of "The Symettry of Sailing" off the shelf tonight.

 

The unbelievers have a "simple" model in which the tide is like a conveyor belt.  (And I'm looking at a system without variables here to ease the explanation).  In that model the angle of the boat to the tide is irrelevant and there can be no lee-bow effect.

 

The technical believers use a complex model in which altering the angle of attack of the hull and foils to the tide alters the force applied to them by the tide.  This in turn affects the force applied by the sails because the forces acting in the two fluids must remain in balance. 

 

GRF's post almost convinced me - but then I stepped back and remembered that the lower fluid in which those forces are working is not the tide but water.  If the water is moving east at three knots and the boat has a force applied to it by the tide which would move it east at 3 knots in the absence of other forces moving it in different directions then there is no angular force on the hull and foils.

Originally posted by fab100 doing 1.01 knots thru the water, against a 1 knot, on the nose, adverse tide.

You're missing a few things. First, if you are doing 1.01 knots through the water when you are slugging that 1 knot tide then if you point up 1 dgree you will drop speed, say to 0.91 knots. Conversely if you point down 1 degree you may go up to 1.11 knots. Then lets consider how big the lateral component of this tide actually is. If its a 1 knot tide and you are 1 degree off bang into it the lateral component is going to be, oh I dunno, I can't be bothered to do the sums, but lets say 0.01 knot (bet its way less than that). So that means that if you point up the 1 degree then after an hour you will be one tenth of a mile downtide and 1 hundredth of a mile cross tide of where you started. Meanwhile the chap who pointed down is 3 tenths of a mile uptide but one hundredth of a mile cross tide. He then puts a covering tack in and sails the two hundredths of a mile needed to be bang in front of you in about a minute and a half in which he gets pushed back two hundredths of a mile by the tide to be that much less than three tenths of a mile ahead of you...

Ah yes, you say, but I can point 2 degrees higher than the other chap and not go any slower. In which case I say congratulations, well sailed, but that means you'd beat him just as thoroughly if there were no tide at all...

Edited by JimC - 13 Oct 11 at 8:56pm