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    Posted: 19 Oct 11 at 7:06pm
Oatsandbeans replay of SG explaination is spot on ...

GRPs attempt at vector addition so far is OK but does nothing to expalin how the magical leebow effect gives any advantage; in this example all the addition of the current does is back the sailing wind ... and of course in this example the converse would be true on the other tack & so even out.

I look forward to the vector diagram explaining how you can sail in a 3knot Easterly with a 3knot westerly flowing tide.
 
Given you no doubt discount anything I (or others) say GRP I refer you to page 109 in Stuart H Walkers book Advanced Racing Tactics ... probably the best ever book written on the subject and quite heavy going.

Chapter 16: Current Fact & Fiction

"There is nothing magical about the "leebow effect". One tack or one jibe may recieve a more advantagious apparent wind than another, but in the absense of wind shifts each boat will spend the same amount of time on each tack and the apparent wind differences will therefore equalise each other"

I fear this thread is an example of the internet giving any idiot a voice ... for the readers of this thread read Walkers book.

Tactics also well covered by Mark Rushall's book Tactics.

GRP will no doubt declare these authours dingo muppets ...


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Posts: 6499 		Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 19 Oct 11 at 7:41pm
No one said there was anything magical about it. Fact is it happens, like a favourable shift. The OP asked what it was, now he knows, wether you choose to use it or not is a tactical decision, which clearly only accumulated experience will decide for you.
The more folk muddy the water, the better the chance for those that do use knowledge of it to their advantage, personally I've clearly been lucky, consistently lucky...
It works for me.
I read walkers book a long time ago, it's written for open sea racing which by and large is true, in open water one tack evens out another. We on the other hand race in coastal water, a mile beat is a long course, race officers rarely move marks unless the wind shifts, three or four races can take place on the same course in diametrically opposite tides, many of us will have raced in circumstances where the tide turns during..
Over the years I couldn't start to count the number of times a lee bow has meant a single tack beat, yet still half the fleet went the wrong way. Or they left the lee bow tack til last and ended up massively over stood. Or they went too early out of a gate start, or started the wrong end of a long line, or they tacked off a tidal knock fetch only to return further back than where they left...
I have always turned to sailing books for tactical knowledge, hence my dismay at reading this misleading advice to a guy simply wanting to know what it was. I never thought for one moment I might be the one counselling dinghy sailors, hence I guess my tenacity in the matter.

Edited by iGRF - 19 Oct 11 at 7:53pm
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Posts: 6499 		Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 19 Oct 11 at 8:11pm
Originally posted by Oatsandbeans



GRF thanks for the intertesting comments on the Flying 15 class. But seriuosly tidal effects are greater on slower boats and I'm sure that a F15 is a lot slower than anything that you sail -so they must know a thing about tides. ( Steve was sailing 470s and Fireballs in the early 80's)
Thanks for the drawings -I liked them, but they didn't really help much. The main problem with you is that you are still thinking of the tide under your lee bow and what it is doing to your boat- this is not usefull. It only confuses things. The tide is not under your lee bow (doing anything magical) the only 2 things that the tide is doing is 1. modifying the wind that your sails are seeing and 2. moving the buoys around in the body of water that you are sailing in. Until you can understand, or just accept this, you will have a problem with this and you will have real mental problems when trying to sort out what to do on the race course.  The beauty of my approach (apart from being right, of course) is that tidal tactics become really simple. Good luck.


Yes difficult sketches they don't show the whole picture. Just like whoever warped your mind, bet they tried the dragging a table cloth with all the little plastic elvstrom boats on it. That's not thinking 3 dimensionally, ignoring the foils, marks don't move, you move, one tack takes you closer to the mark the other takes you further away, fundamental sailing rule comes next, need I teach you egg sucking.
That table cloth trick ignores the fact that there are two opposing foils generating lift when fluid moves over them and the correct angle of attack is applied to BOTH sets.
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Posts: 1459 		Post Options Post Options   Quote sargesail Quote  Post ReplyReply Direct Link To This Post Posted: 19 Oct 11 at 8:37pm
GRF can you confirm that you recognise that the foils are both:

1.  moving through the water - boat speed caused by balanced above and below water forces.

2. with the water at the speed of the tide/current flow.
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Posts: 1151 		Post Options Post Options   Quote 2547 Quote  Post ReplyReply Direct Link To This Post Posted: 20 Oct 11 at 8:42am
Originally posted by iGRF

The OP asked what it was, now he knows...


Your diagrams do not address the supposed "leebow effect" which has been defined a couple of times in this thread as the supposed majical benefit from squeezings ones bow up when sailing directly into tide upwind ... which is a falacy.

All you diagrams poorly show is that the sailing wind will change in the presence of current. Even a pondmonkey would know this. In diagram 3 the boat should really be shown sailing higher.

The change in sailing wind will be the same on either tack and is well illustrated on page 111 of Walkers book & page 17 of Rushalls book. This change in sailing wind is the same regardless of the tide being on the lee or windward bow ...


Edited by seamonkey - 20 Oct 11 at 8:46am
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Posts: 8956 		Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Posted: 20 Oct 11 at 9:16am

Sea Monkey, what has happened? Your last few posts have dispelled my vision of you as an angry, trolling 13 year old, and show you as a well read sailor who can't possibly be GRF's inner demon fighting to get out! Thank you.
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Posts: 4028 		Post Options Post Options   Quote G.R.F. Quote  Post ReplyReply Direct Link To This Post Posted: 20 Oct 11 at 9:30am
Originally posted by sargesail

GRF can you confirm that you recognise that the foils are both:

1.  moving through the water - boat speed caused by balanced above and below water forces.

2. with the water at the speed of the tide/current flow.

OK, try to think of it like this then.

On one tack the foil could be considered to be anchored against the tide current flow, on the other it is able to 'go with the flow'. If that were not the case then when the foil direction changes there would be no increase in pressure and lift on the foil.

Go back to my first example. 

Absolutely zero wind. 

Yet on one tack the boat moves freely across the current. Where is your 'balance' then? If not from the apparent wind generated by the combination of water movement on the lower foil against the static air pressure against the upper foil (the sail).

There are three forces in play when tide is present, trying to suggest it is not there because a boat sitting in water no matter what its attitude reacts the same is what is being suggested to you by these amateur physicists. It may be the case that over an open body of water with uniform pressure across the entire sailing area then the effect can be ignored and there is no 'magic' (not that anyone with any sense ever claimed anything magical) but it is a fact that the lower foil and to a certain extent the hull as well generates lift if it's angle of attack is set against that flow and stabilised by the pressure on its upper foils.

Easily proved all this in a test tank.


Edited by G.R.F. - 20 Oct 11 at 9:40am
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Posts: 1151 		Post Options Post Options   Quote 2547 Quote  Post ReplyReply Direct Link To This Post Posted: 20 Oct 11 at 9:55am
Originally posted by Rupert

Sea Monkey, what has happened? Your last few posts have dispelled my vision of you as an angry, trolling 13 year old, and show you as a well read sailor who can't possibly be GRF's inner demon fighting to get out! Thank you.



I think it's obvious who the troll is here ... that goon who keeps sucking in the feeble minded gibbons in with this perpertual motion theories ...

I hear he used his rig in the water to gain further advantage over the tide at the 100 nationals ... where he finsihed 39th from a fleet of 43 ... thats the kinda guy to should take tactical advice from...

However if you need to know how to air row a beach toy he is d'man ... so he says ...
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Posts: 4028 		Post Options Post Options   Quote G.R.F. Quote  Post ReplyReply Direct Link To This Post Posted: 20 Oct 11 at 10:32am
Originally posted by seamonkey

Originally posted by iGRF

The OP asked what it was, now he knows...


Your diagrams do not address the supposed "leebow effect" which has been defined a couple of times in this thread as the supposed majical benefit from squeezings ones bow up when sailing directly into tide upwind ... which is a falacy.


What is being, has been discussed, as I've said countless times is 'what is lee bow effect', and what has been clearly demonstrated is that some people (me included) refer to it as the effect of a strong tide on the lee bow of a boat having the effect of increasing windward performance on that tack, hence 'lee bow effect'

What is being proffered as a secondary and largely irrelevant suggestion is that pointing  or pinching higher to obtain the lee bow effect may or may not be beneficial and since very often it isn't, the whole lee bow effect theory is debunked.

Alternatively the counter effect sailing in open water with a constant tide evens out any advantage one tack may have over the other is also used to debunk it.

None of which means that there is zero effect when a favourable tide is present at an angle to the lee bow of a sailing craft.

And that really is an end to it.
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Posts: 4028 		Post Options Post Options   Quote G.R.F. Quote  Post ReplyReply Direct Link To This Post Posted: 20 Oct 11 at 10:36am
Originally posted by Rupert

Sea Monkey, what has happened? Your last few posts have dispelled my vision of you as an angry, trolling 13 year old, and show you as a well read sailor who can't possibly be GRF's inner demon fighting to get out! and are a turnturtle gone rogue.


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