Author

Topic: Estimating set and drift

David Burch

posted March 14, 2007 08:55 PM
In figure 1313 of Emergency Navigation, there is a trick procedure for figuring how much you will get set in a current depending on the ratio (current speed)/(boat speed) and on the angle of the current on the bow: broad on the bow, on the beam, or on the quarter.
The formulas are simple and easy to use... and very useful underway, even when not in an emergency.
the caption of that figure states in part:
"With current on the bow, boat speed is retarded by roughly three quarters of the current speed, which is about what you gain with current on the quarter."
In redoing the second edition, this sentence stood out. I am assuming this means that our SMG with current on the bow will be reduced to SMG = S0.75*C and that current on the quarter the SMG = S + 0.75*C.
The exercise is work out a few numerical cases to see if this is true.
From: Starpath, Seattle, WA


