Wow...
- Thread starter Simon Sexton
- Start date
Apparent wind can't be self generated. It is a vector that is created by true wind and boat speed. When the boat is gaining on the current, true wind goes negative. Apparent wind also has to go negative.
It's impossible for the boat to be opposing the current and screaming along at 30 knots at 90 degrees to the destination. In order for the boat to be sailing 90 degrees to destination, it has to be opposing a 10 knot current. If it is opposing a 10 knot current, there is 0 true wind speed. If there is 0 true wind speed there is 0 apparent wind speed (after momentum has been killed by the current) and the boat can't sail.
It might be feasible for a boat to be screaming across the river at 30 knots at 90 degrees to the current with 10 knots true wind generated by the boats movement with the current. But then it is losing ground at 10 knots, isn't it?
Let me ask questions in steps. When a boat is sailing downwind (other than DDW) in 10 knots of breeze with zero current, does anyone disagree that the boat can have a VMG downwind greater than 10 knots?
Yes, however, 90* to the current and 90* to the destination are different. To sail 90* to the destination, it would be necessary to sail upstream at some angle where the vectors from the sailing angle and the current would result in a course that is 90* to the desitination. That of course would begin the process of decreasing airflow, leading to slower speeds, etc, etc.
I wish this hoax had been filmed in a lake rather than a river. All this talk about current this, current that, is nothing but a distraction. Or perhaps deliberate misdirection.
Watch me pull a magic sailboat out of my hat. This thing can cure global warming!!
Watch me pull a magic sailboat out of my hat. This thing can cure global warming!!
I stand corrected. Thanks.
Replace VMG with SOG and the arguement should stand better.
-Will (Dragonfly)
The boat can have a speed through the water or speed over ground that exceeds the wind speed under these conditions. However, without a specific destination, VMG is a meaningless term.
Do not confuse SOG with VMG. In your example if the destination that is upwind of the boat, then the VMG will be negative, i.e., the boat will be sailing away from its destination. To be meaningful, to calculate a VMG there must be a destination. I think a lot of the confusion here is that these two terms SOG (or speed through water) and VMG are being used interchangeably, they are related, but very different concepts and measurements.
This idea ranks right up there with cold fusion and perpetual motion machines.
I don't think so, but I don't know for sure. In SF, they were sailing at what, 50 knots boat speed with 20 knot winds VMG? It was certainly faster to sail the boat on a broad reach than it was to sail it DDW, but does VMG exceed true wind speed? I'd have to see the evidence. I'm guessing, not. But the point is that true wind speed would need to be consistent. If there is no wind, except that which is generated by current, it disappears when the boat opposes current.
Per https://en.wikipedia.org/wiki/Velocity_made_good - Velocity made good, or VMG, is a term used in sailing, especially in yacht racing, indicating the speed of a sailboat towards (or from) the direction of the wind.
If you'd like to think of VMG as a speed to a destination, think of the destination as a point an infinite distance away in the direction opposite the wind.
Yes, definitely. See the YouTube clip of the AC race I posted up-thread. Wind speed during the race was about 11 kts. During the downwind leg the boats had an average VMG over 20 kts.
Thank you for looking that up. I don't know why a school district would block my access to a search engine, go figure.
In racing there is typically a windward mark and a leeward mark, these are very specific destinations. Continuing on with the Wiki definition:
(my emphasis)
I also don't have access to YouTube....
If the VMG was 20kts. the actual boat speed through the water was (or perhaps because the foils) over the water was much higher. But I can't verify that now. If I recall correctly they were also dealing with tidal currents that affected the VMG, but not necessarily the boat speed.
I'm not the bucket list sort of guy, but if I had one, sailing one of these foiling cats (not on, but actually sailing it) would be at the top of my list. In all my years of messing about with boats, both for fun and as a professional, foiling seems the most fun and interesting innovation since I stepped into that El Toro in Sausalito in 1959.
I haven't followed this thread but because it is so long, I finally watched the video.
I don't know what the commentator is going on about, but he keeps saying, "no wind,....no wind,.. no wind", yet every video shows,...wind, on the water, when the tri is sailing.
Kind of reminds me of kids in sailboats that call you on the phone and say, "Dad, can you come out and give us a tow back in, there's no wind"
Then the Dad looks around the harbor,.." No wind,..? Then how come the trees are moving?"
When somebody starts sailing in no wind, wake me up.
I don't know what the commentator is going on about, but he keeps saying, "no wind,....no wind,.. no wind", yet every video shows,...wind, on the water, when the tri is sailing.
Kind of reminds me of kids in sailboats that call you on the phone and say, "Dad, can you come out and give us a tow back in, there's no wind"
Then the Dad looks around the harbor,.." No wind,..? Then how come the trees are moving?"
When somebody starts sailing in no wind, wake me up.
From Wikipedia:
In 2013, a new class of catamaran was announced for the America's Cup which can achieve well in excess of double the speed of the wind.[3] The catamarans used for the 2013 America's Cup were expected to sail upwind at 1.2 times the speed of the true wind, and downwind at 1.6 times the speed of the true wind.[4][5][6] They proved to be faster, averaging about 1.8 times the speed of the wind with peaks slightly over 2.0.[7]
You have to agree with this in order to understand my argument.
In 2013, a new class of catamaran was announced for the America's Cup which can achieve well in excess of double the speed of the wind.[3] The catamarans used for the 2013 America's Cup were expected to sail upwind at 1.2 times the speed of the true wind, and downwind at 1.6 times the speed of the true wind.[4][5][6] They proved to be faster, averaging about 1.8 times the speed of the wind with peaks slightly over 2.0.[7]
You have to agree with this in order to understand my argument.