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Slayer 05-02-2010 09:22 AM

Shortest distance
 
When sailing up wind to a fixed point, over a distance that will require multiple tacks, is there a formula or calculation used to know when to tack as to minimize the actual distance traveled..or distance made good?

itsme6582 05-02-2010 09:51 AM

There are entire books on this. There are a lot of factors that come into play. If the wind doesn't shift and you assume the speed you lose during a tack is negligible then it won't matter if you make one tack or 100.

Here's just one example. Lets assume the wind is coming out of the north and your mark is north. If the wind is shifting to the Northeast, your tacks will have very different results. On a port tack, you will have to point away from you mark as the wind shifts. On a starboard tack, it will be just the opposite. You will point more to the mark as the wind shifts.

Simes 05-04-2010 08:01 AM

Yes there is . . .
 
Hi Slayer,

Some years ago I drew up a small chart that gave the increase in speed needed to make up for moving off the direct line from one point to another.

It is then easy to work out your VMG for any given course either up or down wind.

PM me with your e-mail and I will send it to you.

Regards

Simes

nolatom 05-04-2010 09:58 AM

I think that short of a mathematical "formula" (which may not respond well to windshifts), the basic principles are:

If lifted, stay on it.

If headed, tack, it becomes a lift after you've tacked. So keep watching your compass.

In general, absent windshifts, stay on the tack which takes you closer to the mark than the other tack. But don't let the mark get abeam too early, or you risk overstanding and wasting distance.

It might be useful to picture a "cone" emanating from the mark, each edge of which is about 45 degrees either side if the prevailing wind direction. you want to remain inside that cone so as to avoid overstanding. The cone starts wide, then narrows as you get closer to the mark. While doing the stuff above, when you get near the edge of the cone, or are in doubt about if you're near the edge (which would be the "layline"), it's time to tack and dig back in towards the center of the cone, watching for lifts and headers as you do.

Of course, if the permanent wind direction (as opposed to just back-and-forth oscillations) shifts, then so does the "cone". That's the unpredictable fun of beating upwind.

DrB 05-04-2010 10:19 AM

Nolatom pretty much sums it up
 
Barring no obstacles (land, shallows, traffic, etc.) as you head up to a mark, if you're getting headed I say more than two times, then switch tacks until you start getting headed the other way. If the wind is slowly shifting direction, stay on the tack that is getting the lift (relative to the mark) as long as you can. Once on the header tack, only stay on it as long as you need to cover enough distance so that when tack back to the favored bearing, you can ride it for a while. This minimizes distance traveled and gives to the best VMG to your mark.

DrB

hellosailor 05-04-2010 10:35 AM

If you are just going by the geometry of things, it doesn't matter if you make one tack or ten. In reality...you have to consider wind trends and shifts, and that you'll lose some time during each tack even if they're done perfectly. And covering the fleet (assuming you're racing?) and all the other tactical issues.

You might want to check for articles online (or, gasp, in print) and then do a gut check versus the pro opinions on what's going to work best for you.

ehmanta 05-04-2010 10:47 AM

Don't forget the effects of current. Around the Bay it's generally not too bad but can approach 3 knots in some areas. When you are tacking back and forth, it's good to know which tack the current effects you most, hopefully it's in your favor.:D

Edit: I think that there are too many variables to make any chart usable. It maybe OK for generalizations, but it would not be able to account for current, wind shifts, land breezes vs sea breeze, sea state, particulars of the boat (my boat always sails better on a Starboard tack than a port tack) etc....

Slayer 05-04-2010 10:59 AM

I can visualize how to sail the lifts and tacking when hit with a header. But my question pertains to sailing longer distances. Hypothetically, lets say the wind stands steady on your nose relative to your destination. So whichever tack you are on you are off your mark by 45 degrees. How long should you travel on one tack before flopping over to the other? Or like Hellosailor says above, it does it not matter?

nolatom 05-04-2010 01:42 PM

If you're not racing then you don't need to be as hyper about it. Assuming breeze steady in force and direction (big assumption), it doesn't matter which tack you take first, nor how many (though more tacks mean more time and effort). Just don't overstand, so assuming you're pointing 45, once the "mark", whether in sight or not, gets just forward of abeam, say around 75 degrees relative, tack on over, now it's only 15 degrees off your "new" bow. Keep on truckin' until it gets to 75 degrees off, tack, repeat, repeat...

ste27 05-04-2010 02:17 PM

Quote:

Originally Posted by Slayer (Post 600515)
I can visualize how to sail the lifts and tacking when hit with a header. But my question pertains to sailing longer distances. Hypothetically, lets say the wind stands steady on your nose relative to your destination. So whichever tack you are on you are off your mark by 45 degrees. How long should you travel on one tack before flopping over to the other? Or like Hellosailor says above, it does it not matter?

No wind shift, no current, and no performance difference on either tack... it doesn't matter - assuming you lose nothing in the tack. In our fantasy world of steady wind and no current you should tack exactly at the corner since for every tack you'll lose a little bit

Racing is a bit more complicated and it doesn't actually work the way most people think it does


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