Hi Stuart, thanks for this article - I was literally asking myself the same question the other day. Not because I was used to AWA but because of a specific experience I actually had and thought might be worth adding as a comment: On the Myth of Malham, we made a tactical decision to go south to avoid a wind hole just before the finish. This worked pretty well until we found another wind hole that wasn't in the forecast, right in front of the Needles. I was helming the boat as I always do in no wind, just trying to get it going based on feeling. As my co-skipper was up, I got all his comments, "you're at 90 TWA, can you not come up??" No, I can't - if I want to keep the boat moving. As the boat picked up speed, I could slowly come up. Thinking about it, it occurred to me this was me creating my own apparent - and that maybe looking at AWA would actually be useful here! And it was.. I've never worked with AWA tbh, but I have now created a page on our B&G to display it because I have found that in absolute nothingness of wind, it's a really useful orientation!
The second comment I wanted to make is regarding calibration... And I'm sure this is different by manufacturer. But I also always thought that AWA would be more reliable than TWA if the calibration is off. However, at a seminar on calibration with B&G, they actually explained to us that AWA is just as calculated... What isn't calculated is Measured Wind, and then from there they calculate TWA and TWD - and essentially calculate AWA by deducting log and heading from it again... From what I understood, they would not treat it as more reliable than TWA, which is a shame.
That’s great feedback - thank you. I suspect some of the earlier and lower cost systems are simpler than some and use basic data from the wand. Measured wind speed at the rotor is of course always a direct measurement as you mentioned. When I first started racing I used to work out the next leg wind angle using vector diagrams on the chart in pencil as the instruments we had was just log(boat speed) and wind speed with AWA)
Oh, another question: you mentioned a table about boat speed vs angle gains. Could you elaborate a bit on how your crew derived this, and what the format was? 🤔 I'm aware we're doing this by working on our polars but it would actually be interesting to see the numbers side by side!
Hi Inka - that’s just the polar targets for TWA then adjusted for VMC or (VMG to waypoint) B&G can display the target speed for every wind angle, good when reaching, this is just using the polar numbers which you can upload to the V&G H5000 system if you have it. You then know if you are reaching optimally. However this has nothing to do with your actual progress to the mark which B&G doesn’t do. It will give you VMC to the mark but won’t tell you if you should sail lower to go faster and increase VMC etc. Expedition does this of course. So you then have to tell the helmsman to sail either lower or higher to maximise VMC at that moment in time - then making up the difference closer to the mark. There is so much confusion here and because skippers just plug the numbers into routing software they sometimes forget the basics . VMC = VMGx COS of the angle off. So you can produce a table based on your polar target speeds and degrees off course BTW to see the different VMCs it’s quite illuminating! This is what the routing is doing (plus tide and sea state etc) of course. So having your target percentage on screen is useful but not always useful if you are routing correctly. That’s why I say just keep basic 3 numbers on the mast and put all the other numbers on the cockpit displays and give the helm less to think about so they can focus on feeling the boat through the sea state etc.
Hi Stuart, thanks for this article - I was literally asking myself the same question the other day. Not because I was used to AWA but because of a specific experience I actually had and thought might be worth adding as a comment: On the Myth of Malham, we made a tactical decision to go south to avoid a wind hole just before the finish. This worked pretty well until we found another wind hole that wasn't in the forecast, right in front of the Needles. I was helming the boat as I always do in no wind, just trying to get it going based on feeling. As my co-skipper was up, I got all his comments, "you're at 90 TWA, can you not come up??" No, I can't - if I want to keep the boat moving. As the boat picked up speed, I could slowly come up. Thinking about it, it occurred to me this was me creating my own apparent - and that maybe looking at AWA would actually be useful here! And it was.. I've never worked with AWA tbh, but I have now created a page on our B&G to display it because I have found that in absolute nothingness of wind, it's a really useful orientation!
The second comment I wanted to make is regarding calibration... And I'm sure this is different by manufacturer. But I also always thought that AWA would be more reliable than TWA if the calibration is off. However, at a seminar on calibration with B&G, they actually explained to us that AWA is just as calculated... What isn't calculated is Measured Wind, and then from there they calculate TWA and TWD - and essentially calculate AWA by deducting log and heading from it again... From what I understood, they would not treat it as more reliable than TWA, which is a shame.
That’s great feedback - thank you. I suspect some of the earlier and lower cost systems are simpler than some and use basic data from the wand. Measured wind speed at the rotor is of course always a direct measurement as you mentioned. When I first started racing I used to work out the next leg wind angle using vector diagrams on the chart in pencil as the instruments we had was just log(boat speed) and wind speed with AWA)
Oh, another question: you mentioned a table about boat speed vs angle gains. Could you elaborate a bit on how your crew derived this, and what the format was? 🤔 I'm aware we're doing this by working on our polars but it would actually be interesting to see the numbers side by side!
Hi Inka - that’s just the polar targets for TWA then adjusted for VMC or (VMG to waypoint) B&G can display the target speed for every wind angle, good when reaching, this is just using the polar numbers which you can upload to the V&G H5000 system if you have it. You then know if you are reaching optimally. However this has nothing to do with your actual progress to the mark which B&G doesn’t do. It will give you VMC to the mark but won’t tell you if you should sail lower to go faster and increase VMC etc. Expedition does this of course. So you then have to tell the helmsman to sail either lower or higher to maximise VMC at that moment in time - then making up the difference closer to the mark. There is so much confusion here and because skippers just plug the numbers into routing software they sometimes forget the basics . VMC = VMGx COS of the angle off. So you can produce a table based on your polar target speeds and degrees off course BTW to see the different VMCs it’s quite illuminating! This is what the routing is doing (plus tide and sea state etc) of course. So having your target percentage on screen is useful but not always useful if you are routing correctly. That’s why I say just keep basic 3 numbers on the mast and put all the other numbers on the cockpit displays and give the helm less to think about so they can focus on feeling the boat through the sea state etc.