Join Date: Dec 2008
Location: Calgary, AB, Canada
Thanked 72 Times in 67 Posts
Rep Power: 8
You cannot use a GPS to calibrate a knotmeter, unless there is no current. You might use a Dutch log.
The Dutch Log can be used to calculate boat speed through the water. Position one crewmember on the bow with some floating, organic material; position another crewmember in the cockpit with a stopwatch. The crewmember on the bow tosses the material forward and shouts “mark” when the material passes the bow. The crewmember in the cockpit times the passage from bow to stern. Apply the following formula:
Speed (knots) = 0.6 X boat length (feet) / time (seconds)
ISPA Yachtmaster Ocean Instructor Evaluator
Sail Canada Advanced Cruising Instructor
IYT Yachtmaster Coastal Instructor
ASA 201, 203, 204, 205, 206, 214
As I sail, I praise God, and care not. (Luke Foxe)
Last edited by jackdale; 08-25-2009 at 12:53 AM.