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

As to those who would decry the 'Ferry Gliding' example simply because it doesn't correspond with their lee bow debunkingposition. I would suggest the following.

If you have say a 4knot current one way with your craft headed the other directly into the flow balanced exactly by a four knot wind on a dead run. Brought effectively to a standstill over the ground.

What would happen if the plate gybed to the left (or right) even just one degree (rudder still centred)?

If the others are to be believed nothing would happen. But the fact is the craft would shift right or left even though the water it is sailing in doesn't 'know' anything has happened.

Sorry whatever they're reading it's been misleading them.


Edited by iGRF - 03 Oct 19 at 1:33pm

I am a bit unsure of what GRF is proposing if it’s not the LBE. Please elucidate in as few words as possible

Originally posted by iGRF    and Ferry Gliding clearly is a 'thing' as well.

Ferry gliding is a thing but it is nothing more than the sum of the vectors of the water flow and the power applied by the canoeist.

At a small angle relative to the flow the canoeist can still provide enough thrust to overcome the flow as the frontal area presented to the flow is small. The resultant vector across the flow is small but as it is not countered by anything, sideways progress is reasonable.

If the canoeist tries to go at to large an angle his vector across the flow will be much more rapid however he will not be able to overcome the flow and hence the resultant vector will see him swept down the river.


What is perhaps more of interest regarding this overall discussion is what happens in shallows and near boundaries as this presents opportunities.

Fluid flow will tend to zero speed at walls and boundaries therefore close to the banks or shallow areas flow will be slower. If you change nothing as you traverse a patch of slower flow and don't notice the change in apparent wind (typically and increasing strength with an associated header) then you may miss an opportunity to improve temporarily your vmg.

If my memory is correct the OPs son was in a tidal harbour with changeable depths and therefore it is highly probable that he may have encountered a slightly deeper channel enabling him to utilise a slight lift from the induced change in apparent wind.

Originally posted by iGRF Originally posted by CT249 The fluid dynamics, angle of attack etc do not change regardless of whether the tide is on the lee bow or on the weather bow. The water you are sailing through does not know what the tide is doing. Wrong. Absolutely and totally wrong. It 'knows' because of the forces induced at the foil. This is that same theory that we should consider that we are sailing in a tank full of still water within a tidal 'conveyor' which as i said might be fine for offshore yachts capable of only 7 -8 kts, but not for planing craft where the direction of the flow will impact the lower foil with enough pressure to increased the created wind element. And even then I'd question that tank of water, what if the tank of water was pointed at both ends then aligned fore and aft in the coveyor belt? What if the tank of water had a naca shape and the conveyor were applied to its lee side, nothing would happen right up until the yacht itself came into contact with one end of it and applied force, then everything changes, it's a completely nonsense assertion.

My 2p worth.... and I can see GRF's train of thought in this. I haven't looked at the maths, so could well be wrong but thinking out loud, this is what I see.