Sailing trivia (get in here if you like airplanes and treadmills)

[Blackjack200]

Saw this on sailnet and thought it was pretty interesting. Here's the riddle verbatim:

Boats A and B are identical and sailed by equally skilled crew.

Both are same distance from finish line.

Both are in a ten knot current flowing in the same direction as the boats.

Boat A has ten knot true wind from astern, Boat B no wind.

What will be the result ? A B Tie

Why ?

(Boat A's True Wind is towards the finishing line. . Current is also running towards the finishing line.)

And to be perfectly clear what's going on here, I made this awesome paint jpeg.

 

[PaperclipGod]

Boat A by a nose!

 

[101mpg]

I thought the ideal wind for boats is a left or right quartering headwind since the sail acts like a wing? I don't know about a straight on headwind though if you can get any thrust out of that, but I would think that would be better than having a 0 knot condition (10 knot current negating the 10 knot tailwind)

 

[LTC8K6]

Well, if they were airplanes, the one with the 10kt tailwind would have a 10kt higher ground speed, and would easily win the race.

Should be the same for the boats, I think.

 

[coxmaster]

Well, if they were airplanes, the one with the 10kt tailwind would have a 10kt higher ground speed, and would easily win the race.

Should be the same for the boats, I think.

Thats exactly how i looked at it

 

[Greenman]

I'd say boat A is going to pull ahead.

 

[MikeMike]

Boat B...

Boat A is going to have to slow itself down in order to keep going forward in the direction it wants...

 

[LTC8K6]

Boat B...

Boat A is going to have to slow itself down in order to keep going forward in the direction it wants...

They might lose a little of the advantage of the 10kt wind, but it shouldn't negate the help.

 

[PaperclipGod]

Boat B...

Boat A is going to have to slow itself down in order to keep going forward in the direction it wants...

:hmm:

You saw the picture, right? And you guys do realize that sail powered vessels can use tailwinds...?

 

[LTC8K6]

:hmm:

You saw the picture, right? And you guys do realize that sail powered vessels can use tailwinds...?

It's probably a trap. It seems very obvious that A will win, so it probably won't. :biggrin:

 

[MikeMike]

I really don't know... I took a guess... I could ask my uncle, he did win the Macinac sailboat race (for his class) a year or so ago... I bet he would have an idea

 

[Born2bwire]

If we assume that the boats will be carried along by the water's flow at the same speed as the current, then the wind doesn't matter. The boat without any wind can drop sail so that they do not feel any large effect from the wind created by moving at 10 knots by current into stationary air. The boat with the wind will not feel the wind because it is moving at the same velocity as the wind. Hence, the boat has zero velocity relative to the wind.

So both boats are only being carried by the water's current. It would only matter if one of the boats had a wind at a speed greater than the water's current.

 

[deadlyapp]

It's a question of relative speed. In a ten knot current, and assuming the boat is traveling the same speed as the current (which is probably not a realistic assumption considering they are not a rigid body, there is friction, etc), then the wind has a relative speed of zero in relation to the sailboat. The sailboat sees it as there is no wind, and therefore the two should finish at the same time.

But we don't live in an "ideal" world, so the boat with the tailwind will win because it is much more likely to "actually" be traveling 10kt rather than the other one which is probably traveling slightly slower.

Edit: DAMN born2bwire beat me while I was typing. Shitty!

 

[Born2bwire]

It's a question of relative speed. In a ten knot current, and assuming the boat is traveling the same speed as the current (which is probably not a realistic assumption considering they are not a rigid body, there is friction, etc), then the wind has a relative speed of zero in relation to the sailboat. The sailboat sees it as there is no wind, and therefore the two should finish at the same time.

But we don't live in an "ideal" world, so the boat with the tailwind will win because it is much more likely to "actually" be traveling 10kt rather than the other one which is probably traveling slightly slower.

Edit: DAMN born2bwire beat me while I was typing. Shitty!

Whooo! :awe:

 

[MikeMike]

It's a question of relative speed. In a ten knot current, and assuming the boat is traveling the same speed as the current (which is probably not a realistic assumption considering they are not a rigid body, there is friction, etc), then the wind has a relative speed of zero in relation to the sailboat. The sailboat sees it as there is no wind, and therefore the two should finish at the same time.

But we don't live in an "ideal" world, so the boat with the tailwind will win because it is much more likely to "actually" be traveling 10kt rather than the other one which is probably traveling slightly slower.

Edit: DAMN born2bwire beat me while I was typing. Shitty!

even in the real world though (and i agree with b2bw after reading) if you are moving with the current at 10kt, what friction would be applied to the boat? wind resistance is the ONLY one I can think of...

 

[Blackjack200]

It's a question of relative speed. In a ten knot current, and assuming the boat is traveling the same speed as the current (which is probably not a realistic assumption considering they are not a rigid body, there is friction, etc), then the wind has a relative speed of zero in relation to the sailboat. The sailboat sees it as there is no wind, and therefore the two should finish at the same time.

But we don't live in an "ideal" world, so the boat with the tailwind will win because it is much more likely to "actually" be traveling 10kt rather than the other one which is probably traveling slightly slower.

Edit: DAMN born2bwire beat me while I was typing. Shitty!

Ignoring the effect of wind for a moment, a boat that is in a 10 knot current and moving at 10 knots with the current will not feel any friction.

If the skippers do not do anything, the boat in 0 wind will be slower due to the headwind and will lose. But remember that these are sailboats and we expect the skippers to use their keels, sails, and rudders to their advantage.

No one has gotten it yet, if no one gets it tomorrow I'll post the answer (or at least what I think it is.)

 

[101mpg]

With 0 knot wind speed and traveling at 10 knots with the current then you'll have a 10 knot headwind effectively...because the wind is calm

 

[Blackjack200]

With 0 knot wind speed and traveling at 10 knots with the current then you'll have a 10 knot headwind effectively...because the wind is calm

correct.

 

[deadlyapp]

So are we assuming the sails are up?

By friction I mean there will be losses between the water and the boat until it reaches a completely steady state. The water can definitely flow past the boat keel without acting upon the boat, and it's designed to. Although I'm not a boating person, I'd assume that it would take a bit of time before it would reach steady state and move at the same exact speed.

As I said, if you are not in an ideal world, then boat A will always win. also we would always assume that the boat in no wind would drop sail and reduce its effective drag in all possible ways, but it still would be slower than boat A due to losses.

Edit @ mikemike: There is drag caused by the surface of the water on the boat keel and the effect of the wind on any exposed surface of the boat. Like I said, the water and the boat keel do not act on each other as a rigid body, there is some slip (caused by drag) between the water and the boat.

 

[Humpy]

If the skippers do not do anything, the boat in 0 wind will be slower due to the headwind and will lose. But remember that these are sailboats and we expect the skippers to use their keels, sails, and rudders to their advantage.

It seems that you are hinting that boat B would be able to use its sails, keel, and rudder to sail into the 10 kt headwind and move faster than boat A, which would have zero wind to work with and would rely only on the current.

If that is the case I hope there is a good explanation for it.

I'm no sailor, can sail boat B use a self generated wind to travel faster by tacking(?) back and forth to reach the finish in less time than boat A?

 

[PaperclipGod]

It seems that you are hinting that boat B would be able to use its sails, keel, and rudder to sail into the 10 kt headwind and move faster than boat A, which would have zero wind to work with and would rely only on the current.

If that is the case I hope there is a good explanation for it.

I'm no sailor, can sail boat B use a self generated wind to travel faster by tacking(?) back and forth to reach the finish in less time than boat A?

wtf

 

[edro]

Boat A has a head start based on the photo. He is a cheater and should be disqualified.

 

[LordMorpheus]

With 0 knot wind speed and traveling at 10 knots with the current then you'll have a 10 knot headwind effectively...because the wind is calm

But you can sail into a headwind by tacking back and forth, while boat A has effectively no wind and cannot do any of that fancy stuff, so I'd give the win to B.

 

[Gibsons]

Boat B should never quite reach the 10 knot speed of the water since it's facing some air resistance. Even if its sails are down. Boat A should be able to reach 10 knots, at which point it will experience essentially zero air resistance.

 

[Blackjack200]

But you can sail into a headwind by tacking back and forth, while boat A has effectively no wind and cannot do any of that fancy stuff, so I'd give the win to B.

Winner Winner, Chicken dinner!

Boat B should never quite reach the 10 knot speed of the water since it's facing some air resistance. Even if its sails are down. Boat A should be able to reach 10 knots, at which point it will experience essentially zero air resistance.

That's only true if the skipper points his boat straight into the wind. If he bears off the wind 40 degrees he can beat windward and make upwind progress, thereby reaching the finish line faster.

http://en.wikipedia.org/wiki/Tacking_(sailing)#Beating