Hi
For some time now I’ve been wondering, if at least theoritcally, a sailing boat (or catamaran) could go faster than the speed of the wind?
I know, that practically the resistance of the water will slow down the boat.
What I want to know is, if the size of the sails, and a specific course will generate enough power to accelerate the boat to a higher speed than the actual wind. Some sort of leverage effect?!
I’m not sure, if I clearly formulated my question.
Thanks anyway in advance.
Matth
Well the sail acts as a horizontal aerofoil rather than working by air resistance. This works by having the air on one side (the ‘longer’ curved side) having to take a longer route than the shorter straight distance. Since the air reaches the back at the same time, due to pressure, again pressure crops up because the faster moving air creates a low pressure, and ‘sucks’ the sail towards itself. For this reason it’s technically possible that a sail could go faster than the speed of the wind, and that its maximum speed is probably correlated mainly to the size and shape of the sail, the windspeed, air density (maybe?), and the resistive forces.
Btw I didn’t have time to look up all the technical information on sailboats, so that’s half physics-knowledge and half conjecture /
Soz for double-post but the edit button doesn’t work o.0
Yes easily seen in here:
Wind speed = 0
current speed = 2 mph
the boat will be moving between 0 and 2 mph
Actually now that I think of it the boat might be able to exceed 2 mph since it could be also though of as current speed = 0 wind =2 as there is no absolute velocity.
You’re in a boat kanicbird? I’m not quite sure I understand where you’re getting your information.
This has been discussed several times before so you may want to do a search. Yes, a boat can sail across the wind with a speed numerically graeater than the true wind speed and this does not defy any laws. It cannot sail directly downwind faster than the wind. A boat can also sail to windward at an angle or directly into the wind in the case of specially built boats with rotating sails.
Don’t forget the speed of the tides/current, as well.
Okay sailor, I got one for ya: given a constant windspeed, at what angle does your average 30’ sloop go the fastest? Close reach, reach, abeam, or downwind? Growing up sailing, my dd always claimed downwind. I contend close reach (this might be a remnant of my Hobie 16 days). Anyone?
NurseCarmen, there is no one absolute definitive answer to your question because there are too many variables but it is not like this is classified information and there are plenty of polar diagrams out there in boat brochures and sail magazines. This depends not only on the boat but also the wind speed, the sails, etc. In general terms the lower the wind speed the better you sail across it. As wind speed increases you can point further downwind but as a general rule, say, with a 20 knot wind, and your average set of sails (if such thing existed, it doesn’t) a boat will sail fastest between 30 and 45 degrees off from downwind (in other words, with the wind coming from the quarter).
From the Anapolis Book of Seamanship. Page 43 describes the points of sail:
Baloney. A sail is two dimensional. The airspeed differential between the two sides is minimal.
Bernoulli’s principle only accounts for 4% of the lift of an airfoil. The sail deflects the airflow. Action/reaction. Newton.
Matth:
Draw a rectangle with one set of sides being the wind speed. The diagonal represents the boats course and maximum possible speed. The maximum speed is never reached due to friction.
An iceboat can reach highway speeds in a 20 mph breeze using this principle.
Sorry ronbo, a sail is NOT 2 dimensional. It behaves almost exactly like a wing.
And it is indeed possible for a boat to sail faster than the wind speed, as long as it is not sailing downwind. There is even a term called motor-sailing where you use a motor AND a sail, which helps the boat go even faster. You might think that the motor would make the sail act like a parachute. This might be true with a cigarette boat, but not your normal sloop. Read: Motorsailing.
What’s one thing got to do with the other? A sail has virtually no thickness.
No shit. Did anybody say otherwise?
No shit? I learn every day
I might? Really?
I’m sorry but I don’t smoke.