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

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GarethT View Drop Down
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    Posted: 15 Sep 19 at 4:16pm
I'm really sorry for giving the hornet's nest a poke, but I was watching my son do the Round Hayling windsurf race yesterday.

The current was flooding strongly at the entrance to Langstone Harbour with a light SSE breeze. Beating out was a real challenge. Watching my son, on a port tack he did something with his feet on the board (no idea what!) and he pointed 5 degrees higher, then suddenly was tracking 15 degrees higher and faster compared to the boards around him.

He did it again on starboard beating into the current along the seafront.

Whilst it may not be 'the' thing others have claimed on here, it certainly is 'a' thing.

Edited by GarethT - 15 Sep 19 at 4:20pm
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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: 15 Sep 19 at 6:51pm
Well as I've said time and again it is a 'thing' and I did it twice today to pull myself back from the back to very nearly taking out the leading Contender when he and the rest of the fleet made fatal mistakes in a classic tidal bend in this slow as hell Farr 3.7 in light winds and thanks to a correct tidal call I managed to wire off the inboard steps whilst the contenders who always wire ahead of me were slogging with tide on their weather bow and we're both on the same tack, I just managed to go wide enough to get a better angle, works every time.
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Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Posted: 15 Sep 19 at 7:17pm
Nooooooooooooooooo! Just when the forum was getting busy again...

Didn't we work out that that GRFs Lee bow isn't the same as the classic one (which doesn't exist) and is actually taking the correct tack first to use the tide?
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Post Options Post Options   Quote GarethT Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 19 at 11:01am
I think itís more subtle than that. They were all on the same tack.

In certain wind/tide conditions, high mode will have the current on the lee bow and low mode on the weather bow. With the harbour entrance as a very good example, itís like ferry gliding.
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Post Options Post Options   Quote andymck Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 19 at 11:20am
Totally agree. Itís ferry gliding.
Just about getting set up right but does not allow anything more than that.
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Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 19 at 11:31am
Clown
Originally posted by GarethT

I'm really sorry for giving the hornet's nest a poke
Clown

Originally posted by GarethT

the harbour entrance as a very good example
With such huge variation in current speed and direction across the channel I'd say the harbour entrance is just about the worst possible place imaginable to use as a lee-bow example.
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 19 at 12:25pm
Well you learn something new everyday.. Nice after all this time to pick something up from here, I'd never heard that expression 'Ferry Gliding' had to go and look it up in fact and it talks about berthing boats using the current applied to one side of the bow opposite to the direction in which you need the craft to dock with the power keeping the craft on station, so I can see how the description would apply.

However all those formative years ago, dating back to discussions I used to enjoy with Eric Twiname (I wrote articles for a magazine he was editor of) the term he used was tidal lee bow, so you'll have to forgive me for assuming y'all might understand that.

The fact that some offshore cruising authors rather like the doctors destroying the mmr jab for notoriety, debunked the 'myth' of lee bow is their loss, not ours, it is a fact particularly in the sort of water we as racing dinghy sailors often participate on with tidal curves, varying speeds according to depth and flow channels, it is another fluid like the air we use in the sail, it's a 2nd dimension that can be every bit as important in propelling the boat around fixed marks, so I really don't get why there is even controversy around the subject.

But thanks for the 'ferry gliding' description, I think it's a bit confusing so I'll stick to my tide on the lee bow for now, it is easier to discern on a racing windsurfer it's taken me these fifteen odd years to manage to get anything like that same seat of the pants feel and even now it's a very dull sensation unless it becomes so powerful the difference between wiring and not wiring for example occurs, but even then to the uninitiated that could just be confused with a lifting gust, so it's easy to understand how folk miss it.
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Post Options Post Options   Quote CT249 Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 19 at 12:29pm
Originally posted by GarethT

I think itís more subtle than that. They were all on the same tack.

In certain wind/tide conditions, high mode will have the current on the lee bow and low mode on the weather bow. With the harbour entrance as a very good example, itís like ferry gliding.

It doesn't matter whether the tide is on the lee bow or the weather bow - the tide is still moving you in the same direction. You are effectively on a moving carpet; the angle at which you face while on that carpet has no effect on the way it affects you.

I don't know about Langstone, but in one of the places I sail you only have to be separated by a few feet initially and you can end up in a very different patch of tide, but that's not related directly to your course but only to your position.


Edited by CT249 - 16 Sep 19 at 12:31pm
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Post Options Post Options   Quote CT249 Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 19 at 12:38pm
Originally posted by iGRF



The fact that some offshore cruising authors rather like the doctors destroying the mmr jab for notoriety, debunked the 'myth' of lee bow is their loss, not ours, it is a fact particularly in the sort of water we as racing dinghy sailors often participate on with tidal curves, varying speeds according to depth and flow channels, it is another fluid like the air we use in the sail, it's a 2nd dimension that can be every bit as important in propelling the boat around fixed marks, so I really don't get why there is even controversy around the subject.

But thanks for the 'ferry gliding' description, I think it's a bit confusing so I'll stick to my tide on the lee bow for now, it is easier to discern on a racing windsurfer it's taken me these fifteen odd years to manage to get anything like that same seat of the pants feel and even now it's a very dull sensation unless it becomes so powerful the difference between wiring and not wiring for example occurs, but even then to the uninitiated that could just be confused with a lifting gust, so it's easy to understand how folk miss it.


The mythical "lee bow" effect has nothing to do with "tidal curves, varying speeds according to depth and flow channels" etc. The latter exist; the "lee bow effect" does not.

The mythical "lee bow effect" refers to two adjacent boats that are each encountering tide from exactly the same direction and course. Your example refers to boats that are not adjacent, and are not encountering the same tidal flow because of "tidal curves...depth and flow channels" etc.
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Post Options Post Options   Quote GarethT Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 19 at 12:38pm
Yes, but if your rig is oriented slightly differently, will the impact of the apparent wind from the current also be slightly different?

Edited by GarethT - 16 Sep 19 at 12:38pm
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