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

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iGRF View Drop Down
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 19 at 12:13pm
The fact is if you were to oversheet to that degree without an additional reason for doing it, (getting the tide on the lee side of the foil) you would simply stall out and slip behind. That technique was two fold, back then there were no cambers which tend to control the angle of attack of the rig. The rig in fact was a dinghy style rig, a needle spar mast and possibly a Mountifield (local sail builder)sail. Pressure is applied to the back of the board as well as oversheeting to get the foil across the flow and you'll have to trust me when I say it doesn't work, certainly not as effectively, without the extra pressure you get from tidal flow. Like it to not, it's true, it works and our sub terrainean friend like so many others are wrong when they refer to tidal flow as only a moving carpet to be ignored. I'd say if you want to win stuff on the sea then ignore the tide at your peril.

Edited by iGRF - 17 Sep 19 at 1:50pm
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Post Options Post Options   Quote H2 Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 19 at 12:59pm
I have experienced instances where the fleet was sailing with the wind and tide totally aligned and with the tide just on the windward side and then a small lift  on one part of the course caused those boats to have the tide on the leeward side and the effect of the lift was much more than you would expect from just the lift. The effect of being pushed to windward by the tide was very noticeable compared to those that missed it.
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Post Options Post Options   Quote Oatsandbeans Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 19 at 2:09pm
OK Here goes - my simple explanation for why the LBE is fallacy.

First to get things straight what do I mean by the LBE. (Lee bow effect).
This is the additional advantage that you get from the effect of the tidal flow when it hits the boat (and foils) on the lee bow. This increases the apparent wind and also lifts the boat to windward. This results in greatly improved performance even if it is obtained by "pinching" to obtain it.

Race Scenario 1
The best way to get your head around it is to consider what would happen if we had a race in a strong adverse tidal stream with the course on starboard tack aligned to the tidal flow ( which could just be got onto the lee bow by pinching) where all the marks were free floating. There is uniform tidal strength across the course.

As the marks were free floating ( with sea anchors) unless we looked at the shore line we would not know that we were in a tidal stream. We would experience a wind strength and direction that was a vector sum of the true wind and tidal induced wind, and this would be constant in strength and direction across the course. In this race some boats raced as normal concentrating on boat speed and picking up the minor shifts and others tried to use the LBE by pinching on starboard tack to gain the LBE .
I predict that the boats that pinched on starboard would not be in the lead at the windward mark.

Race Scenario 2
Taking this to the next stage if we now had a race that the buoys were all movable at 3 knots ( think RIBs rather than motorised buoys!). We had the same race with any tide. Would the movement of the marks make any difference to the race. I suggest that they wouldn't.

Race Scenario 3
The next stage is to have a race where we had like race 1 the tide, but we also had like race 2 the buoys moving at a constant speed. This would be just like the result of race 1. This is exactly what we have when we have moored buoys in a tidal stream.

I hope that makes sense. Once you get that the rest drops away.
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 19 at 2:22pm
OK, let me paint you another scenario.

There is zero wind and zero current.

There is a fixed point due North they'd like to race to.

Several craft are scattered randomly along a West East axis.

None are moving and sails are limp.

Slowly an adverse current begins from ENE and gathers strength.

The Fleet begins to drift with the flow due South West, still there is zero wind.

Our Hero lines his craft North South on Port tack....

What do you think happens next?

Edited by iGRF - 17 Sep 19 at 2:25pm
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Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 19 at 2:25pm
That there is no way to downvote sh*t posts is one thing that's wrong with this forum. 

GRF and like minded individuals will spout the same fallacies until everyone gives up and its just becomes sailing version of a flat earth echo chamber. It is funny. And it gets riled up posts in the short term. But I'm not sure such disinformation is great for the forum long term. 


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Post Options Post Options   Quote davidyacht Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 19 at 2:47pm
I wonder whether being lifted on a favorable eddy might be confused for a “lee bow” effect; there is a turning mark in our harbour where if you pinch hard you can effectively be scewed up toward the mark to windward, while making little distance over ground, whereas if you tack you will disappear rapidly down tide and away from the mark, I thought that this was a lee bow effect for years, but I now put it down to the vagaries of different tidal flows and their interaction with localized wind patterns.
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 19 at 2:47pm
I wondered how long it would take for the climate change deniers to turn up.

I'm done, believe what you like.

And Gareth, congratulate No 1 son from me and tell him to ignore dinghy sailors when it comes to advice as to how to sail in tide, particularly RS200 crew ;-)
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Post Options Post Options   Quote H2 Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 19 at 3:10pm
Sorry for having an experience that differs. Lets get back to discussing the same old sh*t, now where was that "why is this forum so sh*t now post??"
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Post Options Post Options   Quote Oatsandbeans Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 19 at 3:19pm
OK GRF
so the tide will induce a tidal wind coming from the WSW ( the opposite of the ENE tidal direction. If our friend is pointing north he will then sheet his sails in or a reach. All the boat will experience this light WSW wind and will start to sail where they want to go using this wind. Wind is the same whether its from the general movement of air or from the movement of water that our boat is sitting on.
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Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 17 Sep 19 at 3:56pm
This is the same old sh*t though. I've linked to two equally bad threads. 

You may have had a different experience. But plenty of people fall for illusions. If you really believe in your experience and have a theory to how it might work, then post up with some numbers and proper examples. More conjecture isn't helping anyone understand anything. Plus, there is a painfully obvious reason why shifts appear larger when sailing against an adverse current; and it's due to land based reference versus water based reference.

What GRF does in these threads is post half baked impossible situations which are phrased deliberately so that no one can really get to the bottom of what he means or what he's trying to say.   When people present him with the numbers he changes focus and hops to a different example which is again completely un-provable. 

I mean, take his example above... if the tide came in and every boat had a 1 knot NE-SW current with no true wind, they would feel an apparent tidal wind of 1 knot from the SW. The 'hero' could be on port tack (gybe). He would sail on a beam reach, but he would have to sail a course quite a way east of due north to ever reach the mark. Of course the only way he could ever get to that mark is by having a boat that sails faster than the wind and by gybing 'downwind' to the mark. If iGRF gave us the distance the mark was from the start point and the strength of the tide it wouldn't take 10 minute to work out what angle and at what speed the boat would have to achieve to reach the mark. I'm not sure if GRF is deliberately leaving out that information or he actually just doesn't have a clue what information would be required to solve his scenario. But at a guess the boat would have to do around 1.33xwind speed at 45 degree from DDW to have any chance of ever reaching the mark. There are a few boats which can do this in 10-15 knots, but I don't know many places that have that much current! 

So what is his point? His scenario tells us nothing about how over sheeting or pinching above the tide makes any difference.  It just tells us that you need a very fast boat to overcome the tide in zero wind. He thinks riddles are clever, but riddles are only clever if they have a solution. Otherwise they're just ramblings.
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