Originally Posted by fryewe
"Seamanship" in this discussion seems to be narrowly defined as the ability to navigate and pilot rather than the broader meaning. And clearly navigation and piloting errors are prime contributors to loss of vessels and crews being placed in danger.
Considering seamanship in this thread using that narrow definition:
- I think that those who go to sea now with near-continuous fix information have a limited understanding of how to translate fix information into what is commonly called "estimated position" or EP. How many who know how to do it still do so with the 3 or 4 GPSs (Plotter/AIS/Handheld/Smart autopilot) giving us continuous fix info?
- In the "old days" when fix information wasn't continuous or necessarily accurate or reliable prudent mariners spent a good deal of time evaluating their navigation data to determine their EP. They realized that EP was the center of a "circle of uncertainty" within which - given various fixed and variable errors in navigation data - the ship would be located but that the EXACT position of the ship could never be known.
- They knew and continuously evaluated the errors that contributed to position uncertainty on the chart:
-- Fix error
-- Set and drift due to current
-- Leeway due to windage
-- Steering error
-- Compass error
and generally kept a hand DR from one fix to the next. They kept the entire circle of uncertainty safe until they could "collapse" the circle with a new fix.
They knew that all charts had errors and carefully evaluated every (paper) chart while voyage planning to understand the age and type of the survey(s) the chart was based on including sounding distribution and method. No one I know does this on a chart plotter.
With all that as background I ask:
- How often do you all evaluate your GPS fix for accuracy when underway? Do you do it periodically or is there some key you use to draw your attention to the need to evaluate fix accuracy? If you have to evaluate accuracy how do you assign error to the fix other than the "plus or minus 16 feet" or whatever the display says? Does your GPS unit signal with an audible signal when it has lost track on enough satellites to get a fix?
- Do any of you still use the concept of EP when navigating with GPS?
- How many of you still hand DR to stay in practice on the odd chance that all your GPS fix equipment goes Tango Uniform on you?
I am sure many don't do true DR anymore and a very dependent on their GPS fixes. Yes our CP as well as smart phone and IPad have audible signals when the lose the fix.
When we travel offshore or in fog we employ our charts and plot positions every hour. First by our estimations, then verified by our GPS fixes . Checks and balances not depending one on method. GPS when working has improved the system of DR.
In passages, races, I have previously taken there wasn't always the array of electronics there are today so that's how I was taught by other more experienced sailors. Even in recent years offshore experiences we have always kept a plotted chart with position. To plot expected course on a paper chart it is necessary to utilize the mitigating factors, current, wind drift or slide, to do the same on a CP you still have to do that. But can be used the same way as a paper chart, with the advantage of having a more accurate position than a circle of certainty that DR gives you.
We have always used the GPS as one of the tools for navigation, not the only one. I would say in my circle about 3/4 still do both DR as well as GPS navigation with about 1/4 whose only knowledge s the GPS.
That being said unless an EMP takes out all the satellites, isn't it fair to say that there are enough means on board to get a fix even if the electrical systems are all off. The position may be off 16 ft, but I trust its accuracy for exact position is more accurate and within my circle of DR position.
Seamanship to me is more than just navigation. It is also the ability to understand how to problem solve issues on your boat as well as continually assess changing conditions in weather, sea state and of curse wind and wind direction. There are so many facets of seamanship.
Some people i have found are great open water sailors, but when placed in confined spaces like NY Harbor, the Chesapeake, or any other closer quarter sailing they are not as confident or competent.