Thanks to all for participating in our little apparent wind exercise. Much of the fun of this Forum is the sharing of information, even if sometimes contradictory.
What we know for certain about the above photo of a Westsail 32 sailing on a close reach 10 miles north of Grays Harbor, WA, here's what I think:
1. SARABAND is most certainly sailing an honest 4.2 knots through the water. There's a bow wave, she is heeling, the sails and 2 slot effects are working to perfection, and the giant gennaker is pulling like a team of horses. In addition, unseen, the bottom is smooth, fair, and streamlined, which, in my experience, can add a full knot in the conditions pictured. And we know the knotmeter had been calibrated. Apparently this "Wow" moment lasted an hour or so.
2. There's seamanship at work here..DK and I are both advocates of having reef ties rove in place when needed. Nothing worse than trying to hang on while threading the bitter end of a reef tie with one hand through a small grommet without going overboard. Even the staysail has long reef ties, ready to go. In addition, the gennaker halyard is external. No unseen chafe on this vessel, the bane of so many ocean passages. No need to have internal halyards when off the wind. Windage aloft is not always a bad thing.
Look, there's radar. You don't navigate the CA and West Coast on a regular basis without radar. Period. And you don't need the radome way up in the air. 10 feet is fine for getting a reliable 4-8 mile view.
3. Is the true wind really blowing 3 knots? No. It takes 3 knots for wind to break surface tension and wrinkles to begin appearing on the ocean's surface. I not only see wrinkles, but small wind waves. My estimate is the TWS is 4-8 knots. PJ is correct, the wind is never steady either in strength or direction. And heavy boats have momentum and can coast through lulls. In addition, who has ever calibrated their anemometer? Can't be done. At least with any accuracy.
I tried to figure out the TWS of the photo using known vectors of BS, AWA, and AWS, all shown on the cockpit instruments. But came up short. Something wasn't adding up and I believe it is the location of the wind sensor, just above the radome, and smack in the sail plan's back wind when the AWA is forward of abeam. In other words if you tried to sail with your bow on SARABAND's transom, your headsail would be luffing due to the disturbed wind.
Having wind sensors aft and pointing aft is most desirable when running downwind. Less so for sailing nearly close hauled, which SARABAND is doing so very well. SARABAND's skipper has noted he is aware of this backwash effect on the wind sensor and its possible influence on AWA and AWS readings.
Lastly, for those unfamiliar about Westsail ratings, for what it's worth, here is NCPHRF's current database. (The Westsail 32s are listed on pages 59 and 60)
http://www.yra.org/PHRF/docs/current_phrf_certs_rating.pdf
Of five boats listed on current NCPHRF, all SHTP veterans, only PATIENCE shows the "hull faired to rudder" modification. It is possible that other owners declared the modification and NCPHRF ignored them. Checking the current US Sailing PHRF handicaps manual online, NorCal PHRF rates the Westsail at 216, as they did in 2010. Five other PHRF regions, including light air regions like Long Island Sound and S.Cal, rate the Westsail at 204
.
Final tally: 4
Yay votes and
7 Nay votes, the
Nays indicating they believe the Apparent Windspeed was different, likely stronger, than the readout.
