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River Sailing: Newsletter Challenge (09/13/05)

Posted September 13, 2005 7:00 AM

The question as it appears in the 09/13 edition of Specs & Techs from GlobalSpec:

You and some of your buddies are out on the river in a sailboat. The air is very still and you have been drifting along with the fast river current. The trip starts to get a little boring after a while (and especially once all the beer is gone) and you want to dock at the next downstream marina. Would setting sail help you travel down the river quicker?

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The Feature Creep

Join Date: Feb 2005
Location: Boston, MA
Posts: 1055
#1

Tacking

09/13/2005 2:14 PM

I guess it would if you had a jib (I think that's what it's called) so you can harness the wind. Even then you might go faster, but lose time because of having to zigzag down the river.
Personally it sounds like to much effort and I'd just drift.

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Power-User

Join Date: Mar 2010
Location: The Canyons of the Ancients
Posts: 341
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#14
In reply to #1

Re: Tacking

06/22/2010 6:29 PM

in a wide river you might not need to zig zag, 1 zig or 1 zag just might put you ahead in the race, and you can win by an inch in a little over 2 hours.

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Commentator

Join Date: Jul 2005
Posts: 65
Good Answers: 4
#2

Out of beer.

09/13/2005 7:05 PM

I would disregard (as irrelevant) the movement of my sailboat to the shoreline. This situation is no different than being adrift at sea. In this scenario, I am effectively needing to go directly upwind. If the destination is upwind, and I have the proper rigging to tack, I would tack! The aerodynamic forces used to describe the ability of a sailors to make headway in the presence of a headwind (a procedure called tacking) don't care about the shore. If, however, the river is too narrow to tack, I'd keep the sails down and put oars in the water to help increase the water's pull, offsetting the wind's drag on my boat. After all, the destination is directly upwind and we're out of beer!

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Participant

Join Date: Sep 2005
Posts: 1
#3

River Sailing

09/13/2005 11:22 PM

No you likely won't go any faster. Possibly could if you have a 150 Genoa or a spinnaker to set and then go wing and wing or hoist up the spinnaker but only if the wind speed is faster than the current is.

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Active Contributor

Join Date: Aug 2005
Posts: 16
#4

sailing

09/14/2005 8:12 AM

Since the wind is very still (read the story), the sail would add more drag, slowing you down. Either drift with the current, or row.

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Power-User

Join Date: Jun 2005
Posts: 104
#5

Tack what?

09/14/2005 11:26 AM

Ok, I agree with the previous post, please read the story. I know for the nautical types, having no wind is somewhat of an engineering condition than an actuality, but assuming that the air is dead, and you are flowing down stream at X m/s, then from the boat's perspective, there would be a headwind of X m/s, but zero speed in respect to the boat and the water, any tacking would get you up-wind, eventually, but much slower than just lowering sail and going with the flow. Tacking requires using a headwind at an angle, forcing the wind to vector in a direction that results in a forward/diagonal motion of the boat with some net forward motion. However, this force vectoring requires some component in the opposite direction of the wind, which will force you to move slower downstream than if you were just to lower sail and catch some rays. Chill out nautical dudes, have one on me and I'll see you at the marina.

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Active Contributor

Join Date: Jul 2005
Posts: 24
#6

beer!!!

09/19/2005 4:10 AM

out of beer!!!!!!!!!, who planned this trip?

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Power-User

Join Date: Jun 2005
Posts: 104
#7

wrong, -2 pts.

09/21/2005 10:53 AM

I'm kind of disappointed that the answer to this story was false. I know we are all human, but it should be pretty common sense that tacking would slow your speed relative to the land. Who regulates the answers here?

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Friend of CR4

Join Date: Dec 2004
Posts: 1995
Good Answers: 35
#8

And the Answer is....

09/22/2005 3:04 PM

As written in the 9/20 issue of Specs & Techs from GlobalSpec:

Yes, setting sail will help, but you'll have to tack. This situation is equivalent to sitting on a very slow-moving (or non-moving) river with a wind coming at you directly from downstream. You can move against the wind by tacking — zigzagging — from one side of the river to the other while making progress against the wind (and moving downstream relative to the water as a result). In the case of drifting in a fast current, the relative wind exists because you're drifting at the river's speed. You can take advantage of that relative wind by tacking, which gets you down the river faster. So it doesn't matter what the situation - a wind over still water or moving water in still air — the sail will see a relative either way wind and you can tack against it to make forward speed. What does matter is that you neglected to bring enough beer...

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Participant

Join Date: Oct 2005
Posts: 2
#9
In reply to #8

Re:And the Answer is....

10/10/2005 2:08 AM

Come on..... How can zigzagging down river ever be faster than going straight. On the other hand maybe I should put a sail on my car and tack down the freeway yet faster!!?? Hmmmm.

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Member

Join Date: Oct 2005
Posts: 8
#10

the wind is still

10/31/2005 8:28 AM

We generally determine wind speed in its relativity to ourselves. However this teaser doesnt give that information. If a breeze is a breeze then it is the wind speed against ourselves. In this case the river is moving and so is the wind. Therefore the wind speed is zero. Putting up a sails will have no effect.

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Anonymous Poster
#11

Re: River Sailing: Newsletter Challenge (09/13/05)

06/18/2009 9:32 PM

If you ride a bicycle on a calm day, you feel the wind in your hair. This is apparent wind. If standing on shore there is zero wind, then the "apparent wind" of the vessel moving down stream will give the boat something to bite into and instead of it merely being carried, it will make "way" on top of the current. Any way on top of the current is effectively extra progress, so tacking back and forth would be a gain.

The biggest issue a sailboat would have on the river, is whether the boat is moving through the water, or merely "with" the water. If it isn't moving through the water and is merely being carried along on top of the current then the boat will have no steerage, and will thus be unable to makes it's way over to any landing area.

Even a small amount of water flowing over the rudder will give steerage. I have done this... going downstream with a tail wind..... in the lee of a bank in a bend of the river, the boat lost steerage.

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Anonymous Poster
#12

Re: River Sailing: Newsletter Challenge (09/13/05)

03/21/2010 5:31 PM

False statements cause one to arrive at a false conclusion. One must assume you have a sail capable of tacking.

Entries #1 and #9 claim you lose time by zigzagging (tacking). If you row a boat perpendicular to the flow of the river you still drift down the river at the same speed. Time is not lost nor gained in this exercise. The extra distance achieved by the tacking does not detract from the speed of drifting downstream. Think of an airplane circling in a very strong wind. That airplane would drift downwind at the same speed as hot-air balloon.

Several entries refer to the drag of the sail. But if the drag of the sail was greater than the up-wind pull of the sail (lift in aerodynamic terms), then sailing wouldn't work in any condition. Ditto for the drag of the hull of the boat. Sailing works because the force vector created by the wind flowing past the sail is greater than all the drag vectors.

Once the wind starts to pull the boat through the water, one will gain steerage.

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Power-User

Join Date: Mar 2010
Location: The Canyons of the Ancients
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#13

Re: River Sailing: Newsletter Challenge (09/13/05)

06/10/2010 10:50 AM

no need to hurry, the beer is never gone.

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Participant

Join Date: Jun 2010
Posts: 2
#15

Re: River Sailing: Newsletter Challenge (09/13/05)

06/29/2010 10:17 AM

Actually if you take the sails down off the mast and tie some weights to them and throw overboard the currant will pull you downcurrant almost as fast as it is flowing, then you and crew can sit back and enjoy your brews while passing the other boats.

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