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Power Helis . Experience RC . Heli-Max

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Off Topics Jokes-Puzzles-Riddles > Annoying brain teaser #3
 
 
spork
Veteran
Location: Mountain View, CA

My Posts This: Topic  Forum		ABT #1 ended up dragging us down the road of ABT #3. But I like this one on it's own, so I'm giving it its very own thread. Standard warning applies.


You're in a sailboat on a day with NO wind. However, there's a 10 knot current taking you directly toward your intended destination. What's the fastest way to get to your destination? Should you drop your sails to reduce drag, or use your sails to get there more quickly? You can only use the energy from the wind and/or water - no paddles, motors, etc.

RC
03-18-2006 02:46 PM
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Grant H
Key Veteran
Location: No where right now....

My Posts This: Topic  Forum		I would not fly the sail.

I would take the sail off and use it in the water as a water parachute.
03-18-2006 02:52 PM
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Teufel-Hundin
Heliman
Location: Saint Petersburg FL

My Posts This: Topic  Forum		Get a better mechanic to keep up the cummins and power there

We use water anchors all the time no diesel then I go with the last post.

If you cant use sails in water then a slight back and forth tack will carry the best speed.
03-18-2006 03:39 PM
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rcmike
Senior Heliman
Location: Dickson, TN

My Posts This: Topic  Forum		Flag down the guy blazing past you in the boat with a motor in it.
03-18-2006 04:29 PM
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zoom boy
Key Veteran
Location: N.E. Lincolnshire UK

My Posts This: Topic  Forum		How about turning the boat 90 degrees to the current, so that the current is pushing more of the hull, and dropping the sails and doing what Grant H and Teufel-Hundin said.
03-18-2006 05:48 PM
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bagobitz
Veteran
Location: saddleworth,lancs,UK

My Posts This: Topic  Forum		current will always flow faster than the object being carried with it,the drift will be opposed by an APPARENT wind ,in opposite direction to the water-flow(current)and passage of the object. if sails are deployed on this object and it can be steered, it can traverse the currentby utilising ths airflow over the sails....BUT,as the sails have the ability togo downwind about 45*,-the object would move downstream at a faster rate than the waterflow-rate.

in the example,if a container, virtually submerged( with a similar ratio of submerged area/dry area,as the boat) is tossed over the side, the 2 should float along at the same rate. as soon as the hull,and/or sails are used to harness the hydrodynamic "lift" of the keel,or aerodynamic lift of the sails, the boat will move downstream faster.

marks out of ten?
03-18-2006 08:57 PM
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GimbalFan
rrProfessor
Location: Copter County, Nv

My Posts This: Topic  Forum		edit

"How about turning the boat 90 degrees to the current, so that the current is pushing more of the hull, and dropping the sails and doing what Grant H and Teufel-Hundin said" -- Zoom Boy

Forget your Wheaties today, Zoom? If you did that you'd be presenting more surface area (the portion of the hull above the waterline) to drag against the still air. I doubt the extra surface area presented to the water would make up for it.

And by the way, Mr. Spork, you're by NO means off the hook for ABT #1!

op-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-t
03-18-2006 09:36 PM
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zoom boy
Key Veteran
Location: N.E. Lincolnshire UK

My Posts This: Topic  Forum		We arnt talking about a lot of drag here, the speed is very low, remember drag is proportional to v^2, which in this case isnt big, I think there would be more benefit in turning it than any losses, so all thats increased is the area, which is a ^1 factor, so either its going to make no difference or there may be a benefit.

If it increases speed then V^2 goes up, there wont be drag on the hull from the water since the flow would be from the rear (or side) so that leaves a tiny increase in aerodynamic drag, but since that can never be above 5.14m/s the drag is going to still be tiny, and thats at its most.

I dont think you have to worry about it.

Anyway the most it ever could be would be 5.14m/s, using the sales in the water should get the boat closer to that speed.
03-18-2006 11:10 PM
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webbhost
Key Veteran
Location: england - Leicester

My Posts This: Topic  Forum		No wind would mean that any movement from the boat would surely cause drag. However how about turning the boat to move with the current, and turning the sails so that it from the front of the boat you only see the poles (sails going down width of boat)

If there is a tiny gust of wind, it might speed up the boat a little, but because its going down the line of the boat, it makes no difference drag wise because the pole that holds the sail will be there regardless?

AM i close or am i talking stupid?

meh
03-18-2006 11:18 PM
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GimbalFan
rrProfessor
Location: Copter County, Nv

My Posts This: Topic  Forum		"use your sails to get there more quickly?" -- Spork

I contend that nothing done with the sails can improve the velocity of the boat relative to the destination except dropping them to reduce drag.

"If there is a tiny gust of wind" -- Webb

The parameters of this Teaser state that the air is calm. For the sake of discussion, gusts are not a factor.

op-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-t
03-18-2006 11:25 PM
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spork
Veteran
Location: Mountain View, CA

My Posts This: Topic  Forum
Quote 
And by the way, Mr. Spork, you're by NO means off the hook for ABT #1!


I'm in no way considering myself off the hook. However, it seems I've had the last word on that (so far). I assume that means everyone has read my final post and now agrees completely with everything I've said. Perhaps people have simply given up trying the change the mind of the village idiot.


Quote 
I contend that nothing done with the sails can improve the velocity of the boat relative to the destination except dropping them to reduce drag.


DOH! The sails are the ticket on this one. If there is a constant velocity of the air relative to the water it doesn't matter whether the air is moving and the water is still, or the water is moving and the air is still (or any combination thereof). Any framework that is stationary, or moving at constant speed (but not rotating) is an "inertial" frame. Einstein tells us that every single inertial frame is just as good as another with regard to the laws of physics.

So... imagine you're in this situation, and you're in the middle of a thick fog. You can't see anything off the boat due to the fog. However as you stand on the deck you feel a 10 knot breeze in your face. If you're on a sailboat with the sails down, and feel a constant 10 knot breeze in your face, you can tack into that breeze. So you raise the sails, and tack into the relative wind.

If you aren't comfortable with this stop and think about the fact that the air actually is moving. In fact it's going about 1000 mph as the earth turns on it's axis. And it's going almost 67000 mph as the earth goes around the sun. But you say "that's B.S., it doesn't matter that the whole problem is hurling through space, it only matters how fast the air is moving relative to the water". To which I say "EXACTLY".

And if you buy this, I claim it proves ABT #1 as well.

RC

P.S. I'm sure I'm not off the hook for this one yet either. But shall I annoy further with ABT#4?
03-19-2006 02:14 AM
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Mark C
Key Veteran
Location: Houston, TX - USA

My Posts This: Topic  Forum
Quote 
I'm in no way considering myself off the hook. However, it seems I've had the last word on that (so far). I assume that means everyone has read my final post and now agrees completely with everything I've said. Perhaps people have simply given up trying the change the mind of the village idiot.


Your'e kidding right?

I'm still waiting for you to tell me what is spinning the propeller when the cart is going as fast as the wind. I'll ask the question one last time.

Mark C.
03-19-2006 02:17 AM
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GimbalFan
rrProfessor
Location: Copter County, Nv

My Posts This: Topic  Forum		Professor Spork, you're starting to make sense to me. I'm very frightened. My mind is beginning to unboggle and I'm askeered of what I might see.

I was all set to argue the tack point until I realized that a boat making added speed while floating with the water current is the same as a boat tacking upwind which is the same as a boat making added speed while floating with the water current which is the same as a boat tacking upwind which is...

By George, I think I've got it!

The boat tacking upwind is making forward speed in still water. No reason at all that shouldn't also work in a water current through still air.

Now, please tie this epiphany to the prop cart in terms we can understand.

op-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-t
03-19-2006 02:22 AM
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spork
Veteran
Location: Mountain View, CA

My Posts This: Topic  Forum
Quote 
Spork said:
I'm in no way considering myself off the hook. However, it seems I've had the last word on that (so far). I assume that means everyone has read my final post and now agrees completely with everything I've said. Perhaps people have simply given up trying the change the mind of the village idiot.


Quote 
To which Mark C replied:
Your'e kidding right?


So I'll break it down.

"I'm in no way considering myself off the hook."

Not kidding. I don't consider myself off the hook until I've convinced you, or you've convinced me. If you just give up because you've had it with me, I think I've failed.


"However, it seems I've had the last word on that (so far)."

Not kidding. I'm not saying I have proven my point by absolute assertion. I'm just saying that last post is mine at the moment. I'm eagerly awaiting your next post (in which you tell me it all makes sense now - kidding). In point of fact I'm ready to digest your next post and either be swayed by it myself, or rebut it.

"I assume that means everyone has read my final post and now agrees completely with everything I've said."

Kidding - of course. Perhaps I forgot to put a smiley.

"Perhaps people have simply given up trying the change the mind of the village idiot."

Half kidding. By the looks of it there are a lot more people reading these posts than replying to them. I'm sure at least half of them have concluded that I'm a raving lunatic. I long ago came to realize that I have to take solace in the fact that truth never really comes down to a vote.

Quote 
I'm still waiting for you to tell me what is spinning the propeller when the cart is going as fast as the wind. I'll ask the question one last time.


DOH! You added that after I wrote this post. I didn't realize I had left that question on the table. I will respond to that in the original thread (so as not to confuse the threads more than need be).

RC
03-19-2006 02:27 AM
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GimbalFan
rrProfessor
Location: Copter County, Nv

My Posts This: Topic  Forum		"I have to take solace in the fact that truth never really comes down to a vote." -- Professor Spork

Educated men (and women) have been taking solace in this fact for centuries, often to the exclusion of solace from any other source.

I often wonder how full of solace Galileo Galilei's last years were, imprisoned in his own home as he was for having published the truths he'd found.

op-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-t
03-19-2006 02:34 AM
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spork
Veteran
Location: Mountain View, CA

My Posts This: Topic  Forum
Quote 
Now, please tie this epiphany to the prop cart in terms we can understand.


Okey dokey. I'll try. Despite my claim above about not mixing the threads, I'll answer that one here (since it has as much to do with ABT#3 as it does ABT#1).

So GimbalFan, at the risk of taking ridicule from all the sane members of the forum, it seems you agree with me on this one. So...

You buy that the boat being pushed along by the current in still air can tack into that air to beat the current itself to the downstream destination.

A sailboat is nothing more than a bobber with two wings. One sticks up into the air, and the other sticks down into the water. If the air is still and the water is moving you can just turn the whole thing upside down to visualize it as follows. Rather than seeing the boat as tacking upwind into the relative wind, you can look at it as tacking downstream in the current (with the sail acting as the "keel" in still air). So the current is the propelling force on the keel, yet the boat goes downstream faster than the current. Sound familiar?

RC
03-19-2006 02:38 AM
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GimbalFan
rrProfessor
Location: Copter County, Nv

My Posts This: Topic  Forum		Yes. Please continue.

op-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-thwõp-t
03-19-2006 02:41 AM
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Mark C
Key Veteran
Location: Houston, TX - USA

My Posts This: Topic  Forum
Quote 
So... imagine you're in this situation, and you're in the middle of a thick fog. You can't see anything off the boat due to the fog. However as you stand on the deck you feel a 10 knot breeze in your face. If you're on a sailboat with the sails down, and feel a constant 10 knot breeze in your face, you can tack into that breeze. So you raise the sails, and tack into the relative wind



When you raise the sails to tack you will never attain a velocity that has a foward component equal to 10 knots. If the world were perfect and you tack at 45 degrees left you can hope to go 7.07 knots to the left and make 7.07 knots up but that is all.

If you were anchored prior to this you will move toward a fixed point at VMG of 7.07 knots. If the wind you felt was the result of a current that was moving you toward that fixed point at 10 knots you will slow your VMG by 0.23 knots and thus you were better off with your sails down.

Mark C.
03-19-2006 02:41 AM
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spork
Veteran
Location: Mountain View, CA

My Posts This: Topic  Forum
Quote 
I often wonder how full of solace Galileo Galilei's last years were, imprisoned in his own home as he was for having published the truths he'd found.


Don't know, but Newton died a virgin - which seems perhaps a worse fate

On an almost completely unrelated note, I was surprised to learn that Einstein's first wife deserves an immense portion of the credit for the astonishing revelations that are credited almost solely to him. Sad that she is hardly a footnote. It's also interesting that most pictures of Einstein depict a man in his 60's when every one of his major breakthroughs came before the age of 30!
03-19-2006 02:42 AM
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da_man
Key Veteran
Location: Northern CT

My Posts This: Topic  Forum		Does it not matter because current will always push it at 10 knots.

I am not trying to overthink it, usually gives you an inncorrect result.

Real Men NEVER apoligize for being themselves
03-19-2006 02:45 AM
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Off Topics Jokes-Puzzles-Riddles > Annoying brain teaser #3
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