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This is not what they are talking about. It's always step one to get past to understand what's going on here. I don't believe DDWFTTW has been achieved on wate

This is not what they are talking about. It's always step one to get past to understand what's going on here. I don't believe DDWFTTW has been achieved on water.

jasonwatkinspdx 5y ago
You are mistaken. It has been achieved, and the fastest race boats today do it routinely. This is one of the reasons you don't see spinnakers on boats like the America's Cup AC72s, AC50s, F50s, huge open class trimarans, etc. I'm not sure the first boat to achieve it, but it wouldn't be surprising if it was done during the Clipper era. Those boats held 24 hour records from 1860 something all thee way to the 1980s, where modern racing yachts finally eclipsed them.
- aaron695 5y ago
  I think we just have different definitions. It's about the "Directly" You need a propeller to go Directly Downwind Faster Than The Wind as far as I know. I think on water it has to be very large. I expect there are other ways other than a propeller but haven't seen them. A half way definition (This isn't DDWFTTW to me either), I'd like to know if an America's Cup boat could beat a balloon? So it would be allowed off the 'race track' but it has to come back to meet/beat the balloon at the narrow finish line. So it would cover a much larger distance than the balloon and still beat it to the finish line. Is this possible in practice? The Veritasium video doesn't actually answer this, it kinda goes around it. [edit] If it's symmetrical which it should be, as long as they are going downwind faster than the balloon, they just reverse it at the halfway point and get back inline with the balloon but ahead.
  - jasonwatkinspdx 5y ago
    I know what you meant. You are mistaken. Look at the 180 degree data on the polars for AC72 or Bank Populaire. They're more efficient at a broad reach, but they can do it a few knots faster than the wind.
    - aaron695 5y ago
      Why does the Blackbird use a propeller, why not a simple high-performance land sail boat like the Greenbird, a design that fits with the original idea from the sailing community? There is nothing online that says a sail boat can go DDWFTTW. DDWFTTW is at least a 4 decades old term in the sailing community looking at magazines. Here's a design from 1985 using a propeller https://issuu.com/latitude38/docs/latitude3894apunse/162 https://issuu.com/latitude38/docs/latitude3894apunse/162 Sorry, you are mistaken.
      - cblconfederate 5y ago
        the sails on those sailboats act like a wing even downwind . That's only usable with racing boats which use light foils fly over water instead of heavy keels , but yes they can move faster than the wind . Curiously i can't find a good explanation of their design. The Blackbird cannot use a land sail to go faster because it needs something to act like the keel on a sailboat and provide a counterforce. The propeller is an elaborate way to provide that force
        aaron695 5y ago
        You are agreeing current sail boats can go DDWFTTW which is directly downwind not a degree either way, faster than the wind, for a indefinite period of time? Tacking is not allowed, since that's not directly downwind. This should also mean going directly upwind is practically possible, not a degree either way, directly upwind for a indefinite period of time with sails. Do you have a link for this? Here's a link to a working directly upwind rotary sail boat model - https://www.youtube.com/watch?v=j1bR5hb8RCQ https://www.youtube.com/watch?v=j1bR5hb8RCQ
        cblconfederate 5y ago
        I dont know much about sailboats but i think they mean this: https://en.wikipedia.org/wiki/Wingsail https://en.wikipedia.org/wiki/Wingsail . when they are at a slight angle and in combination with lightweight foils pointing the other way it seems they are able to go faster than wind in any direction, without anything like a propeller. In any case i think talking mixing wings, sailboats and propellers makes it confusing to understand what the blackbird does

This is not what they are talking about. It's always step one to get past to understand what's going on here. I don't believe DDWFTTW has been achieved on water.

jasonwatkinspdx 5y ago

You are mistaken. It has been achieved, and the fastest race boats today do it routinely. This is one of the reasons you don't see spinnakers on boats like the America's Cup AC72s, AC50s, F50s, huge open class trimarans, etc. I'm not sure the first boat to achieve it, but it wouldn't be surprising if it was done during the Clipper era. Those boats held 24 hour records from 1860 something all thee way to the 1980s, where modern racing yachts finally eclipsed them.

aaron695 5y ago
I think we just have different definitions. It's about the "Directly" You need a propeller to go Directly Downwind Faster Than The Wind as far as I know. I think on water it has to be very large. I expect there are other ways other than a propeller but haven't seen them. A half way definition (This isn't DDWFTTW to me either), I'd like to know if an America's Cup boat could beat a balloon? So it would be allowed off the 'race track' but it has to come back to meet/beat the balloon at the narrow finish line. So it would cover a much larger distance than the balloon and still beat it to the finish line. Is this possible in practice? The Veritasium video doesn't actually answer this, it kinda goes around it. [edit] If it's symmetrical which it should be, as long as they are going downwind faster than the balloon, they just reverse it at the halfway point and get back inline with the balloon but ahead.
- jasonwatkinspdx 5y ago
  I know what you meant. You are mistaken. Look at the 180 degree data on the polars for AC72 or Bank Populaire. They're more efficient at a broad reach, but they can do it a few knots faster than the wind.
  - aaron695 5y ago
    Why does the Blackbird use a propeller, why not a simple high-performance land sail boat like the Greenbird, a design that fits with the original idea from the sailing community? There is nothing online that says a sail boat can go DDWFTTW. DDWFTTW is at least a 4 decades old term in the sailing community looking at magazines. Here's a design from 1985 using a propeller https://issuu.com/latitude38/docs/latitude3894apunse/162 https://issuu.com/latitude38/docs/latitude3894apunse/162 Sorry, you are mistaken.
    - cblconfederate 5y ago
      the sails on those sailboats act like a wing even downwind . That's only usable with racing boats which use light foils fly over water instead of heavy keels , but yes they can move faster than the wind . Curiously i can't find a good explanation of their design. The Blackbird cannot use a land sail to go faster because it needs something to act like the keel on a sailboat and provide a counterforce. The propeller is an elaborate way to provide that force
      - aaron695 5y ago
        You are agreeing current sail boats can go DDWFTTW which is directly downwind not a degree either way, faster than the wind, for a indefinite period of time? Tacking is not allowed, since that's not directly downwind. This should also mean going directly upwind is practically possible, not a degree either way, directly upwind for a indefinite period of time with sails. Do you have a link for this? Here's a link to a working directly upwind rotary sail boat model - https://www.youtube.com/watch?v=j1bR5hb8RCQ https://www.youtube.com/watch?v=j1bR5hb8RCQ
        cblconfederate 5y ago
        I dont know much about sailboats but i think they mean this: https://en.wikipedia.org/wiki/Wingsail https://en.wikipedia.org/wiki/Wingsail . when they are at a slight angle and in combination with lightweight foils pointing the other way it seems they are able to go faster than wind in any direction, without anything like a propeller. In any case i think talking mixing wings, sailboats and propellers makes it confusing to understand what the blackbird does