tag:blogger.com,1999:blog-4237678261594285909.post6800458921058278630..comments2024-10-01T08:44:22.500-04:00Comments on Sailboat Instruments: Boat and wind speed calibrationUnknownnoreply@blogger.comBlogger4125tag:blogger.com,1999:blog-4237678261594285909.post-7621160832704787852011-02-22T16:07:43.831-05:002011-02-22T16:07:43.831-05:00Thanks! Will test this once the temperature rises ...Thanks! Will test this once the temperature rises here!Erikhttps://www.blogger.com/profile/10896128673707323955noreply@blogger.comtag:blogger.com,1999:blog-4237678261594285909.post-75168418568282036662011-02-22T10:34:56.929-05:002011-02-22T10:34:56.929-05:00OK, here is the approach to use when the true wind...OK, here is the approach to use when the true wind speed (TWS) is larger than the boat speed through water (STW).<br /><br />First, how to recognize the situation? This will happen if, when the boat is at the position of minimum apparent wind speed (AWSmin), the wind comes from behind.<br /><br />In this case, in a calibrated installation, the semi-amplitude of the AWS curve will be equal to the corrected STW value, and the middle of the curve will be higher that the corrected STW value. If not, the whole AWS curve has to be scaled until its semi-amplitude is equal the corrected STW, and the scaling factor becomes the wind correction factor.<br /><br />The formulas to use are then:<br /> STW_corrected = (SOGmin + SOGmax) / 2 (UNCHANGED))<br /> Boat_Speed_Correction_Factor = STW_corrected / STW (UNCHANGED)<br /> <br /> Wind_Speed_Correction_Factor = 2 * STW_corrected / (AWSmax – AWSmin)<br /><br /> Speed of Current during test = (SOGmax – SOGmin) / 2 (UNCHANGED)<br /> True Wind Speed during test = (AWSmax + AWSmin) * Wind_Correction_Factor / 2<br /> <br /><br />Then, if we suppose that, in the example above, the wind came from behind at AWSmin, we would have:<br /><br />STW = 6.69 kts<br />SOGmin = 4.36 kts SOGmax = 7.38 kts<br />AWSmin = 1.56 kts AWSmax = 4.16 kts<br /><br />STW_corrected = (4.36 + 7.38) / 2 = 5.87 kts (UNCHANGED)<br />Boat_Speed_Correction_Factor = 5.87 / 6.69 = 0.878 (UNCHANGED<br />Wind_Speed_Correction_Factor = 2 *5.87 / (4.16 – 1.56) = 4.52<br /><br /><br />Speed of Current during test = (7.38 – 4.38) / 2 = 1.51 kts (UNCHANGED<br />True Wind Speed during test = (4.16 + 1.56) * 4.52 / 2 = 12.91 ktsMerlinhttps://www.blogger.com/profile/00901116173524809046noreply@blogger.comtag:blogger.com,1999:blog-4237678261594285909.post-84864292753073489102011-02-19T16:16:21.696-05:002011-02-19T16:16:21.696-05:00I made some tests and I realized that the approach...I made some tests and I realized that the approach described here is valid as long as the motoring boat speed is larger than the true wind speed. When the true wind speed becomes larger, another approach should be used. I’m working on it.Merlinhttps://www.blogger.com/profile/00901116173524809046noreply@blogger.comtag:blogger.com,1999:blog-4237678261594285909.post-53188675682840426562011-02-19T07:19:16.320-05:002011-02-19T07:19:16.320-05:00I understand why the STW line crosses the SOG line...I understand why the STW line crosses the SOG line in the middle of the curves, but how about the AWS, what is you calibrate with 15 knots of wind?Erikhttps://www.blogger.com/profile/10896128673707323955noreply@blogger.com