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» Online Classroom   »   » Public Discussion of Inland and Coastal Navigation   » 50-90 Rule for estimating current speed

   
Author Topic: 50-90 Rule for estimating current speed
David Burch


 - posted June 19, 2009 11:09 PM      Profile for David Burch           Edit/Delete Post 
Back in 1987 we invented a technique for estimating tidal current speeds and published it in a book called Fundamentals of Kayak Navigation, now in its 4th edition. We still use this valuable Rule today in our text book, Inland and Coastal Navigation.

We have just learned the the US Power Squadron has discovered this early work of ours and now uses this Rule as part of their standard teaching. They have even developed a form to evaluate it, which is quite useful. They treat this Rule now like the Rule of Twelfths for tide height, whose origin is lost in history. The origin of the 50-90 Rule, however, is not lost. We are flattered by this recognition of our work, and hope one day they will learn and acknowledge the source.

We have posted a copy of this form in our online Library, or you can download it here: Form for 50-90 Current Rule

From: Starpath, Seattle, WA
David Burch


 - posted October 28, 2009 08:15 PM      Profile for David Burch           Edit/Delete Post 
As a follow up, we have been told that the USPS now print an acknowledgment on the 50-90 work form, which is much appreciated. It appears to have been a simple oversight, or actually the origin may have been temporarily lost. We do know the rule is presented in several textbooks without any acknowledgment.
From: Starpath, Seattle, WA


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