I know an ice boat can sail on a reach many times the speed of the wind, but can it actually be faster then the wind, directly downwind? My physics senses tell me that a ice boat can’t go faster then it’s power source, but various ice boating folks tell me that it’s done all the time.
I propose a race. A race between a DN class ice boat and a balloon. The course will be directly downwind, let’s say 3miles, the width of the course, unlimited, to allow the ice boat to tack as far as possible. The ice boat and balloon will start on the fly moving directly downwind at the wind speed. The ice boat will be free to steer in any direction in order to make the most speed downwind after the race starts. The balloon must not touch the ice, nor climb higher then the top of the ice boats mast(as to not gain any advantage in wind gradient). At the finish line the ice boat and the balloon must be within 20 yards of the directly downwind course line. As for wind, lets say 15 mph. Lets race on a cloudy day, to reduce the wind variation due to convection (if that’s even possible over ice)
I’m betting on the balloon.
I’m guessing the above wiki quote was calculated after tacking was completed. The boat didn’t sail directly downwind.
Agreed - sailing directly downwind at greater than the wind’s speed is equivalent to sailing directly upwind, which is more or less impossible.
But did the ice boat actually “beat” the wind? I’ll concede that the ice boat travels further and faster than the wind at a tangent, but will it beat a balloon in a fair race? What a lovely segment of Mythbusters that would make.
This isn’t true, although it does seem like it ought to be true.
Given the proper design, it is quite possible to make a wind-powered craft that moves downwind faster than the wind is blowing.
Oh great! Iceboat on a treadmill. Thanks oodles.
Here’s a PDF document that discusses iceboat performance in some detail. Included are results of tracking an iceboat with a recording GPS receiver.
A bit more than halfway down is a diagram that shows an iceboat heading about 20 degrees from downwind, doing 70mph with an 18mph wind.
Ack! A treadmill! That is not fair!
It was because of devices like the one in your link that I inserted “more or less” in my post.
But it should also be noted that it’s something of a stretch to call that sort of propulsion “sailing”. To make that happen with a boat, you’d need a propeller (or the equivalent) to act upon the water.
I’ll believe a gps receiver to measure speed, I will mistrust handheld wind-meters or human guesstimates of windspeed. That’s why I want a race against a balloon.
I think it’s a safe bet that if the wind measurement/estimate was 18mph, the real wind was 60+.
Make that: “the real wind was not 60+”
You should check out this awesome column, published in the Chicago Reader:
Is Ditka drivin’?
We need to keep in mind that the OP isn’t if it is possible to go faster than the wind. Most definitely it is possible to go much faster than the wind. It isn’t possible though to go faster than the wind if you go directly downwind as Cecil himself states in the above linked article.
So the OP put another way is: Does the extra speed achieved by tacking make up for the extra distance traveled while tacking?
This wiki entry says:
“The extra speed gained by zigzagging downwind more than makes up for the extra distance that must be covered.”
I do kknow enough to dispute it.
By zig-zagging (tacking) the runners of an ice-boat or keel of a water boat perform equivalently to a propeller.
If you dispute this, then you will find it difficult to explain how an ice skater propels himself or a fish or sculling boat for that matter.
Alright, I’m convinced. Thanks for all the great links and explanations.
But I still want the race, preferably with a young Henne in the balloon.
Propellers, ice skates, and oars all move relative to the object in question, and can be used to add energy to the system.
An ice boats runners are fixed to its hull. There is sort of a skating motion while it’s turning, but the claim here is that its speed advantage comes while on a steady course at an angle to the wind.
I think Robot Arm has said it rather well. There is a notable difference between what is done by the runners of a iceboat and by the skates of a skater.