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Sailing in tide..quiz. |
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sargesail
Really should get out more Joined: 14 Jan 06 Location: United Kingdom Online Status: Offline Posts: 1459 |
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Topic: Sailing in tide..quiz. Posted: 02 Oct 17 at 9:54pm |
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So tell me why it wouldn't have been faster for blue to do a hybrid of the two: short tack like red and then do a starboard leg from the end of the headland until meeting the port layline drawn?
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sargesail
Really should get out more Joined: 14 Jan 06 Location: United Kingdom Online Status: Offline Posts: 1459 |
Post Options Quote Reply Posted: 02 Oct 17 at 9:51pm | |||
Exactly - so I'm not worried about the header!
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KazRob
Far too distracted from work Joined: 22 Oct 16 Location: Scotland Online Status: Offline Posts: 245 |
Post Options Quote Reply Posted: 02 Oct 17 at 9:43pm | |||
Are you sure you didn't just get lucky taking a flier?
Still don't understand your tide assisted speed or your lee bow stuff. When you head back out from the shore the tide is heading NE-ish so you should get pushed that way and in a reduced wind strength. I can see if you made it to where the tide runs west you will get more breeze but your still being pushed away from where you want to go. |
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Post Options Quote Reply Posted: 02 Oct 17 at 9:37pm | |||
So do I get any brownie points for getting it right?
You'd also imagine the boats coming out of the headland on port would get a tidal lift, of course as they went further right they'd know they'd have to come back in the corresponding header (I just think he tacking angle out of the headland on port would be better). But the above scenario is just the tide changing the apparent wind. I want you to explain how changing mode in tide can lead to a better VMG.
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iGRF
Really should get out more Joined: 07 Mar 11 Location: Hythe Online Status: Offline Posts: 6496 |
Post Options Quote Reply Posted: 02 Oct 17 at 9:28pm | |||
So this is actually what happened. Blue arrives at island before red tacks to cross channel. Edited by iGRF - 02 Oct 17 at 9:31pm |
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Post Options Quote Reply Posted: 02 Oct 17 at 9:22pm | |||
I don't see that there is a uptide gain south of the line, the way iGRF has shown it, the tide just runs straight into that arm of the harbour. Even still, you'd have to sail a header off the line on port to get there. When you do get there it will be a headed shore (divergent breeze) anyway. If there was a strong eddy you may gain, but all that effort to get over that way would be swept away when you hit the tide coming in northerly and north easterly. That tide would also give you another apparent header.
Coming up to the port layline late would feel pretty awful. Yes, the tide would be on your transom, but it would also be giving you a header.
Damn straight there.
Edited by mozzy - 02 Oct 17 at 9:23pm |
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KazRob
Far too distracted from work Joined: 22 Oct 16 Location: Scotland Online Status: Offline Posts: 245 |
Post Options Quote Reply Posted: 02 Oct 17 at 9:06pm | |||
Sorry - I don't understand what you mean. If you're sailing out into the tide you are also going backwards with the tide relative to the wind so the 8-10knts you talk about would be 3-4knts slower (or whatever the tide was). If you're moving backwards relative to the wind I also can't see how the board got more air under the nose to help it lift either. I spent many years on boards and have not long bought a big ol' raceboard again, so sailing a board v a dinghy is not completely alien to me. Explain again please? Perhaps it was just plain old windier over there which isn't the same as some magic tide trick
Edited by KazRob - 02 Oct 17 at 9:15pm |
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sargesail
Really should get out more Joined: 14 Jan 06 Location: United Kingdom Online Status: Offline Posts: 1459 |
Post Options Quote Reply Posted: 02 Oct 17 at 9:04pm | |||
No Graeme just busy working....but looking forward to hearing exactly how you think you won it. So my strategy would have 3 parts. 1. Take the 'free' southerly uptide gain behind the promontory immediately to the south of the start line. I would want to be careful of any potential race on the headland. I'd reckon that right would probably pay, depending on the exact shape of the land and the feel of the breeze. Hopefully I'd have some shifts to help me get there efficiently. 2. I think I'd then sail a short starboard leg until I reached the port layline. This would come quite early because of the east going tide in the east side of the bay. I'd be worried about what sort of tidal compression I'd experience around the island - if it's strong then I would have made the wrong call. 3. For the rest of the race I'd make ground up tide when in less tidal flow, for example in the tidal lee of the island. That is to say I'd emerge as far west as I could without overly compromising my speed. If I thought there was going to be a significant increase in north going tide (a race) to the immediate west of the island then I would execute a different strategy. I would sail a long port tack first and flick on to starboard when I got to the layline for the mark, or, depending exactly on my tacking angle, before that, in order to take advantage of the maximum flow in the main channel before being tidally sheltered behind the southernmost headlands. But I'd still look to flick back on starboard and approach from uptide - remembering that this is predicated on a strong race off the island. |
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iGRF
Really should get out more Joined: 07 Mar 11 Location: Hythe Online Status: Offline Posts: 6496 |
Post Options Quote Reply Posted: 02 Oct 17 at 9:00pm | |||
Pretty much exactly what the coach suggested, he drew it on a board, had he not done so I might not have even bothered, but it was too good an opportunity for an I told you so moment.
The temptation for the cliffs, and yes maybe a back eddy swirl around St Annes head had almost the entire fleet doing as you describe, but the other route, bang over to the left where there was also a bit of a lift off the land, sufficient to get the nose into the tide and give a fair run out into the bay where the full blast of it not only lifted the nose but put the board on the plane, turned the the 8 - 10 knots into 10 to 12 knots which is marginal planing for a race board which reached the island whilst the fleet were still tacking up the coast in slacker air (which also lifts up and over those cliffs. But fundamentally it was tide initially on the nose then full on the lee bow which did it. So much so, that by the island the board had to be sailed free onto a reach. |
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Post Options Quote Reply Posted: 02 Oct 17 at 8:58pm | |||
Sorry, don't really read technique.
One thing I don't get, in the same sentence you say the tide is flooding in and they tried and failed to get the race off before it fully flooded. By 'fully flooded' do you mean 'high tide', or is 'fully flooded' max current? I guess the latter? Also, no depth chart, so I'll assume there's no funky bathymetry or banks? I'd start middle line. Against the tide (does it run that far down?) there will likely be sag, and if you are expecting the wind to go back left you don't want to be on the right of fleet. The shift is right phase so you'd want to sail starboard first if you are expecting it to go back left. I'd also go left up the beat to get in to the shore away from tide which is pretty much with the wind. There may also be a left shift with convergent wind on the left shore to add to the oscillation left you are expecting. Coming in to the windward mark you'd experience a tidal lift in apparent wind too. You'd have to be careful not to over stand the windward mark though. You'd want to get a good transit on the reach and crab down as the traditional fleet windward arc will be even more pronounced with the tide pushing people high. Not much to do on the bottom reach unless there is a tide line where the tide splits which you'd want to get the correct side of. Ultimately, only you were there, so you could say anything worked, and we'd have no recourse.
Edited by mozzy - 02 Oct 17 at 9:03pm |
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