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post #1 of 8 Old 04-26-2009 Thread Starter
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Up wind sailing

Hello:

When sailing to a destination that is directly up-wind, at say, 18 or 30 nm; what’s the best approach?

I’m getting use to my recently purchased Bavaria 44 and when sailing closed hauled (35-40 degrees off the wind) we can do 7+ knts. When gong to our favorite up-wind destination I’ve been trying to sail as closed hauled as possible thinking that this approach is going to get me there faster.

Recently while looking at the Polar diagram of similarly designed yachts ( http://www.beneteauusa.com/wps/wcm/r...PTE_061106.pdf ) I noticed that if you crack off 10 degrees (50 degrees off the wind) from closed hauled, theoretically, you gain 1 knt and if you go off wind another 10 degrees (60 degrees off the wind) you gain another knot of speed.

My question is, when sailing to a destination that is directly up-wind should I try to go as fast as possible at 35-40 degrees from the wind or go 50-60 degrees off the wind to gain 1-2 knts of speed?

By the way, what’s scalloping; and if it is what I think does it work as well going 35-40 degrees off the wind or is it better at 50-60 degrees off.

La Bestia

Last edited by labestia; 04-26-2009 at 07:44 AM.
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post #2 of 8 Old 04-26-2009
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I don't really know how to answer your question but does your GPS show VMG? That would probably be the easiest way to determine the best trade off against point of sail and boat speed.

On the race course it seems everyone points as high as they can, and that has prety much been my approach when crusing to upwind destinations, but I'd love to hear if there is a better way.

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post #3 of 8 Old 04-26-2009
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The Question you are asking is exactly what a tactician does on a race boat. It is a time, speed and distance problem. A America cup crew will go to windward tacking back and forth staying very close to the numb line. When they throw a tack they can do it losing very little speed. So it is faster for them but it is nothing but work. One tack after another after another.

For the average cruiser, you have to make a plotting exercise out of this. Let's use the 30nm example. Draw a straight line between your start point and your end point. Now draw a line 50 degrees off your start point out to where a line 50 degrees off your end point crosses. That will be your tack point. Measure your distance.

30 nm at 7 kts = 3 hr and 20 min's

now lets say that the 50 dregres off course measures 32nm,

8kts divided by 32nm = 4 hours.


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Last edited by bubb2; 04-26-2009 at 08:36 AM.
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post #4 of 8 Old 04-26-2009
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Labestia—

Do the math. Is the extra speed gained enough to compensate for the extra distance traveled. In the case of a monohull, it often isn't. They just don't make up enough speed to offset the longer distances. A multihull on the other hand generally does. It probably depends quite a bit on the wind speed as well...

Two examples:

To get to a windward destination 30 NM away....

If sailing at 60˚ off the wind requires you to sail 48 nm... and sailing 45˚ off the wind requires you to sail 42 nm, but sailing at 60˚ allows you to sail at 6 knots vs 4 knots.. then you get 8 hours versus 10.5 hours... so yes, it would be worth it.

If sailing at 60˚ off the wind requires you to sail 48 nm... and sailing 30˚ off the wind requires you to sail 39 nm, but sailing at 60˚ allows you to sail at 7 knots vs 6 knots.. then you get 6.85 hours versus 6.5 hours... so no, it would not be worth it.


I think what you're calling scalloping is sailing a close-hauled course and heading up as the wind strength increases to take advantage of the change in apparent wind and then falling off a bit as it weakens, to prevent stalling the boat. This practice generally yields the best boat speed but leaves a "scalloped" track, if viewed from above. AFAIK, it doesn't make much sense to do this if not sailing close hauled, since you can easily trim the sails to have the same effect... Sailing close-hauled, the sails are trimmed in for maximum effect and can not be trimmed to adjust for the increase in wind, so the boat's course is adjusted to take advantage instead.

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Last edited by sailingdog; 04-26-2009 at 08:41 AM.
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post #5 of 8 Old 04-26-2009
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There's an easy way to figure VMG using a vector diagram. Draw your straight line from A to B. Now from A draw a line that's 35 degrees to that line; draw another that's 50 degrees to that line. Using a scale of one centimeter = one knot, mark a point called C on the 35 degree line 4.5 centimeters from A to represent a speed of 4.5 knots. On the 50 degree line, mark a point D at 5.5 centimeters to represent 5.5 knots. Now, from your original line AB, draw two lines 90 degrees from AB to the two respective points C & D. If the line from AB to the 35 degree point C is closer to B than the other, then your VMG for close hauled is better. You can measure from A to each of the points along AB to find your actual VMG for that angle of scale by using 1 cm = 1 kt.

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post #6 of 8 Old 04-26-2009
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You also need to factor in sea state and currents, and factors such as the "curl" of the wind around a land feature, like a point, both of which are generally more of a dead reckoning overlay to the math of the GPS SOG reading, the apparent wind, and staring at your polar diagram.

Firstly, the polar is an idealization. Your halyard tension, your genoa car, the distribution of your ballast, your hull smoothness and your helming may all be different from the assumptions that go into the polar. A broad generalization you already have: "cracking off" on a close reach instead of close-hauled will move the boat faster, but only practice between two distant fixed points (like two buoys three or four miles apart more or less in line with the typical winds) will get you used to your boat's capabilities, rather than what the math suggests is "ideal".

The very fact that the winds fluctuate is going to screw your math up anyway...a two-minute "puff" or "lift" to the mark is going to give you a false impression. This is why the dynamic environment of sailing is challenging: the math helps one to understand more of the factors involved, but it can't always provide the solution to the most efficient way to sail a boat over time and a given course.

I found racing on triangular courses helped me develop my instincts in this regard, as well as judging the success of skippers who went "inside" or "outside" of the layline compared to the rest of the pack. The winning boat is frequently the maverick that doesn't know where the wind is, but where it will be likely to be found.

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post #7 of 8 Old 04-27-2009
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There is one further consideration to keep in mind. Since you are not saying that you are "racing" to the upwind destination, the question has to be asked - does it matter what is the absolutely quickest route? Isn't "what is the most comfortable and safest point of sail?" an equally valid question?

Having done the entire "thorny path to windward" from Florida to Grenada, I can tell you the "shortest" or even "quickest" route is often also the "stupidest". Beating your boat up against the seas and against the trades, is not the smartest decision, especially with a family on board, if cracking off a bit can smooth the ride and keep the spray out of the cockpit.

Just my 2 cents worth...

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post #8 of 8 Old 04-27-2009
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Quote:
Originally Posted by labestia View Post
Hello:

I noticed that if you crack off 10 degrees (50 degrees off the wind) from closed hauled, theoretically, you gain 1 knt and if you go off wind another 10 degrees (60 degrees off the wind) you gain another knot of speed.
We can do some pretty simple math to answer this question theoretically.

VMG = boat_speed*cos(angle_to_destination)

(For a sanity check, if we are going directly towards the destination, the angle is 0, cos(0) = 1 and VMG = boat_speed. If we are going 90 deg to the destination, cos(90) = 0 and VMG = 0.)

So given your scenarios:

Boat speed of 7 knots, 40 deg to destination VMG = 5.36 knots
Boat speed of 8 knots, 50 deg to destination VMG = 5.14 knots
Boat speed of 9 knots, 60 deg to destination VMG = 4.5 knots

As previous posters have mentioned, it really depends on a lot of other factors as well. But the simplistic case above shows that it usually isn't worth it to fall off for more speed.
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