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G.R.F. View Drop Down
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    Posted: 13 Oct 11 at 11:38am
Originally posted by Ian29937

A wonderfull rambling thread as usual. 
 
The question is not whether the tide has an impact on the apparent wind as clearly it will.  The question is whether or not pinching to shift from "tide on the windward bow" to "tide on the leeward bow" mode works or not. 
 
The theorists say no, some people say experience indicates yes.
 
I've certainly been overtaken whilst trying to pinch up and gain a leebow effect by people sailing normally to the true apparent wind so my experience dictates that the academics are correct.  Smile
 
Ian

No, that wasn't the question, the question was 'what is lee bow effect'. and what does it do?

The answer to which I've already given.

What then developed was itty nitty picking, the answer to your bit was no not always, pinching in tide is never a good idea, unlikely that you could even pinch to that large a degree that the tide would shift from the weather to the lee bow, it might shift from the nose to the lee bow and tide on the nose is better than tide on the weather side of the foil for all those fluid dynamics equations that I failed to list above..
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Posts: 6662 		Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 11 at 11:36am
To have a mag article you'd have to agree on what "this effect" is first... A sailing in tide series wouldn't be a bad idea for the mag, hink its been a while.

GRF seems to be talking about tactical considerations affecting which tack you should take first. I hope no-one is going to disagree that the tidal stream profoundly affects tactical considerations, most especially since by and large tidal sailing is done in places where the tidal stream and direction is anything but constant.

The direction and strength of the tide also affects the wind direction felt on the boat: if you've got 5 knots of tide from East to West and 5 knots of wind from Nth to Sth then the boat is effectively sailing in about 7 knots of wind from the North West...

If the boat can do 5 knots though the water on a beat then on one tack it will be making 10 knots across the ground heading west, and on the other tack about 7 knots across the ground heading north west, but on both tacks it will be making 5 knots through the water...

Why this gets complicated is that the marks are fixed relative to the ground, not relative to the water, so in this example, compared to the water the boat is sailing on the windward mark is travelling east at 5 knots.

What GRF seems to me to be saying is that when in doubt always sail the tack that is getting you nearer to the mark quickest, because if the tide stream isn't constant you win, and if it is constant then you don't lose. Seems uncontroversial to me...
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Posts: 350 		Post Options Post Options   Quote r2d2 Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 11 at 11:16am
Originally posted by G.R.F.

Originally posted by sargesail




But can we agree that that push is the same no matter where the boat is pointing?

No, we can't agree on that either.

If it were a boat with no means of propulsion then yes we could agree with your 'theory'

But it isn't, it's a sailboat with two sets of foils set in a plane at the conjunction of two 'fluids' moving in different directions.

If the fluids were both moving in the same direction, then yes the push would be the same no matter where the boat was pointing.

But the moment you introduce a means of resistance against either fluid force, then that produces an equal and opposite response <insert all sorts of maths and physics bollox>

Now come on, you must see the sense of this...


In all seriousness here for a second and joking and banter aside, have there been no books or lectures or videos about sailing in tide, tidal currents, waves fast and slow, how to spot them all this stuff we're bantering about here? I can't believe over the years somebody hasn't already detailed it, somebody y'all might actually believe that is.. I bet if my name was Bethwaite y'all would be going ooh ahh it must be true then...
 
GRF you'll never get that v-twin thing finished if you stop to write a book for us!
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G.R.F. View Drop Down
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Posts: 4028 		Post Options Post Options   Quote G.R.F. Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 11 at 11:11am
Originally posted by sargesail




But can we agree that that push is the same no matter where the boat is pointing?

No, we can't agree on that either.

If it were a boat with no means of propulsion then yes we could agree with your 'theory'

But it isn't, it's a sailboat with two sets of foils set in a plane at the conjunction of two 'fluids' moving in different directions.

If the fluids were both moving in the same direction, then yes the push would be the same no matter where the boat was pointing.

But the moment you introduce a means of resistance against either fluid force, then that produces an equal and opposite response <insert all sorts of maths and physics bollox>

Now come on, you must see the sense of this...


In all seriousness here for a second and joking and banter aside, have there been no books or lectures or videos about sailing in tide, tidal currents, waves fast and slow, how to spot them all this stuff we're bantering about here? I can't believe over the years somebody hasn't already detailed it, somebody y'all might actually believe that is.. I bet if my name was Bethwaite y'all would be going ooh ahh it must be true then...


Edited by G.R.F. - 13 Oct 11 at 11:12am
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Ian29937 View Drop Down
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Posts: 409 		Post Options Post Options   Quote Ian29937 Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 11 at 11:00am
A wonderfull rambling thread as usual. 
 
The question is not whether the tide has an impact on the apparent wind as clearly it will.  The question is whether or not pinching to shift from "tide on the windward bow" to "tide on the leeward bow" mode works or not. 
 
The theorists say no, some people say experience indicates yes.
 
I've certainly been overtaken whilst trying to pinch up and gain a leebow effect by people sailing normally to the true apparent wind so my experience dictates that the academics are correct.  Smile
 
Ian
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Posts: 705 		Post Options Post Options   Quote Steve411 Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 11 at 10:46am
Anyway, I'm looking forward to the Inlands this weekend... LOL
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bert View Drop Down
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Posts: 584 		Post Options Post Options   Quote bert Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 11 at 10:21am
so for this to have any effect the wind & tide have to be at diffent angles to each other.
correct? or Not?
May be a couple of people who understand this effect & would be willing to write a summary for the mag & these would be considered to be publised. 
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Posts: 1532 		Post Options Post Options   Quote Pierre Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 11 at 8:56am
Still no pictures I see....
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Posts: 1459 		Post Options Post Options   Quote sargesail Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 11 at 7:44am


I'm of the camp definitely yes. Simple geometry can demonstrate it by saying: if you have East going tide of 5 knots with a westerly wind of 10 knots (so both in the same direction) and you are floating (pointing north for arguments sake) and stationary in the water, how much wind do you feel? Answer should be 5 knots. If the tide turns and you have a 5 knot west going tide against the wind you will feel 15 knots of wind.

As you are not moving through the water do you call this apparent wind? Doesn't matter really, because in the same situation with a moving boat the tide is making a difference for the same reason as above. The difference will be less because of apparent wind due to boat speed. Now you can take this further by saying as long as their is a component of tide against the wind and it is pushing from the leeward side of the boat you will get some lift towards the wind.

Can we agree on that?


[/QUOTE]

You will get pushed towards the wind - yes.

But can we agree that that push is the same no matter where the boat is pointing?
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sargesail View Drop Down
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Posts: 1459 		Post Options Post Options   Quote sargesail Quote  Post ReplyReply Direct Link To This Post Posted: 13 Oct 11 at 7:42am
Originally posted by G.R.F.

Dude you use the tablecloths

I'll stick to the experience of thirty five years and countless victories gained sailing in tides of all different descriptions and directions in all manner of craft.

While I might not be a God like figure of the early days of windsurfing I have a few wins myself - some of which I have attributed to lee bow effect.  But I have seen the error of my ways....
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