NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Measuring (and Calculating) Dip
From: Brad Morris
Date: 2013 Mar 6, 14:06 -0500
From: Brad Morris
Date: 2013 Mar 6, 14:06 -0500
Hi Bill Thanks for the data. Using a theodolite will certainly yield a more precise measurement of the results. Solving for tsub0 using Dr. Young's recommended method is not within my grasp at this moment. Defining the temperature at the boundary layer (tsub0) by this method requires expertise I do not have, yet. I solved for tsub0 directly. That is, knowing the other values, find what the boundary layer temperature would have to be. I also included the negligible wave height correction. At a peak to trough 10 cm, the wvhtCorr'n is under 1 second. WvhtCorr'n=atan((wh/2)/(3860*sqrt(HoE)) Dip=5.04*sqrt(.1123*HoE+tsub0-tsubh)-wvhtCorr'n > Height of eye : Dip: tsub0 > 1.85M : 3'.62 :23.31C > 2.30 : 3'.85: 23.32C > 2.82 : 4'.00: 23.31C > 3.43 : 4'.40: 23.38C > 4.55 : 4'.65: 23.34C Now that raises an interesting conundrum. The boundary layer temperature of the air is higher that either the air temperature at the height of eye or of the surface water temperature. The wave height correction is on the order of a few seconds. Some things have occurred to me 1) The air temp is rounded to the nearest degree C. However, when using 22.5C or 23.5C for the temp of the air at the height of eye, tsub0 remains LARGER than tsubh or water temp at the boundary. This cannot be. 2) The air at tsub0 is warmed by the friction with the water?? 0.3 deg C seems too much for this. 3) The theodolite is out of calibration. hahahaha....Okay Bill, I had to write it down, we know your equipment is good. 4) Could you describe the procedure by which you derived the Height of Eye. A theodolite produces measured angles, yet you are describing the height of eye in meters. Perhaps this is the source of the conundrum. I have also pinged Dr Young with this result, to keep him appraised of our experiments. Best Regards Brad On Wed, Mar 6, 2013 at 12:49 AM, Bill Morriswrote: > ________________________________ > > Brad > > Here are some data for you to play with. The dip was measured with a Wild T2 > theodolite, reading to single seconds and the height of eye with a staff and > the same thedolite. My wife consented to hold the staff while the water > lapped at her feet. > Wind speed variable, 3 to 5 metres/sec. Light overcast 7/8ths. > Air temperature 23 deg C > Water temperature at surface 21.2 deg C > Waves height: about 10 cm > Height of eye : Dip > 1.85M : 3'.62 > 2.30 : 3'.85 > 2.82 : 4'.00 > 3.43 : 4'.40 > 4.55 : 4'.65 > > Enjoy! > > Bill Morris > Pukenui > New Zealand > ---------------------------------------------------------------- > NavList message boards and member settings: www.fer3.com/NavList > Members may optionally receive posts by email. > To cancel email delivery, send a message to NoMail[at]fer3.com > ---------------------------------------------------------------- > > : http://fer3.com/arc/m2.aspx?i=122654