Sailing across tide.
Printed From: Yachts and Yachting Online
Category: Dinghy classes
Forum Name: Dinghy Yarns...
Forum Discription: Tell us your sailing stories
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=4013
Printed Date: 26 Jun 25 at 5:15pm
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Topic: Sailing across tide.
Posted By: Hernia55
Subject: Sailing across tide.
Date Posted: 06 Mar 08 at 11:06pm
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The situation is this, it is a day with wind against tide and I want to reach across them. Most people I see bear away and crab across the tide, I think there is a different approach. In my Laser I have had some success with pointing at the mark and pulling up the daggerboard. As I understand it this helps because my boat has a much smaller wetted surface area than the crabbing boat. I haven't heard this mentioned anywhere else, is it just me? Is this genius or madness? |
Replies:
Posted By: JohnW
Date Posted: 07 Mar 08 at 2:11am
There could be a reason you havent seen this anywhere else. I think you can answer your own question by considering the following: Lets say the tide is 2 knots left to right and the wind is blowing right to left. The mark is 1 mile dead ahead. Now consider the no tide situation which I believe is equivalent: The wind is 2 knots stronger (equivalent to the apparent wind increase from the tide pushing you upwind at 2 knots) compensating for no tide. You want to intercept a launch that is doing 2 knots right to left (the mark would be pulled through the tidal water at 2 kts by its anchor, so this the equivalent in the no tide case ) the launch is currently 1 mile dead ahead. Do you: A) estimate where the launch will be to intercept it and aim for that point sailing as fast as you can (ie bear off from a beam reach with dagger board set correctly for the point of sail) B) pull your board up and point your bows at the launch so that your boat sails with on a beam reach but with lots of leeway (right to left) compensating for the movement of the launch (right to left). |
Posted By: Hernia55
Date Posted: 07 Mar 08 at 6:39pm
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Madness then, good, just so I know. There is of course a tradeoff between the skin friction of the daggerboard and the induced drag of hull and foils. By pulling up the daggerboard you induce more lee-helm and so have to reduce the angle of attack of the rudder to a similar angle to that on a crabbing boat. So I guess the question is whether a Laser goes quicker sideways with the board up or forwards with the board down. Since I have only sailed in these conditions against other Lasers on a few occasions I guess that the difference could also be that (a) I'm a lot lighter than the people I was sailing against or (b) they were sailing too low anyway. |
Posted By: JimC
Date Posted: 07 Mar 08 at 8:22pm
| When you say board up how far up do you mean? Most boats need so little board area when reaching, especially broader reaching that they tend not to make significant leeway until the board is so far up that the steering goes funny. |
Posted By: Guests
Date Posted: 09 Mar 08 at 7:05pm
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Your question has been answered in part, but it's never a judgement call
that can be stated, there are to many variables. I'm no laser sailor, but would guess it depends on the wind strength. If the wind is that light that the tide speeds cumulative effect is more important then we'd leave the plate down.. (By cumulative effect I mean a 4knot tide gives a 4 knot wind 8knots cumulative if they are diametrically opposed, but the escalator effect is obviously still present) If on the other hand you're near planing, then you have room to manouvre and your ploy would be common practise in a sailboard fleet, or a half measure applied. It all depends.. There are other issues, wind against tide equals waves, does you laser surf better without the plate, then the surf effect will give you more apparent wind as a trade off against the lessened resistance from having it down. So for a genuine solution to a tactical problem, you kindof need to give all the details, wind speed, tide speed, wave height, is the wind steady or gusty (makes a difference as to sailing high or low on a reach) how many others in the fleet and what position you're in when it occurs, different positions call for different measures. |