Measured mile Southampton water

[matt1]

Was trying to calibrate the log up Southampton water earlier today but try as I might I couldn't find the respective special mark transits. In each case (North and South) I could find each of the seaward special mark but not the corresponding mark behind them to line up the transit. Anyone know if they have been removed, or overgrown? They are still marked on the Navionics charts I bought a week ago, so in the end I used my GPS track to reset the calibration run

 

[Poignard]

Many years since I used them and all the marks were there then but you can still use the seaward marks alone if you line each up with some two fixed things on the boat (ie take a transit) or take a relative bearing.

Not quite as accurate because the separation between the distance between the two things on the boat you line up with will be considerably less than that between the inner and outer marks but it would do for general use.

 

[ithet]

Was trying to calibrate the log up Southampton water earlier today but try as I might I couldn't find the respective special mark transits. In each case (North and South) I could find each of the seaward special mark but not the corresponding mark behind them to line up the transit. Anyone know if they have been removed, or overgrown? They are still marked on the Navionics charts I bought a week ago, so in the end I used my GPS track to reset the calibration run

In the modern era don't we just calibrate via the GPS? Motor in one direction along tide, record GPS speed, turn 180deg not touching throttle, record GPS again. Speed trough water at that setting is average (add together, divide by two) of the two GPS readings, tide is half the difference.