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post #1 of Old 09-20-2011 Thread Starter
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Great Lakes Boaters, Polyconic charts, mph

I use miles and mph exclusively for speeds and distance for navigation. On another thread, other posters were surprised I use mph and miles. I have been navigating the great lakes for 30 years on my own boats and an additional 10 years in the early 60s on my dad’s boat. It has always been the only way to do it for me. Understanding the significance of the nautical mile, I was curious also why I use miles instead of nautical miles.

For cruising, my wife and I travel extensively in the Great Lakes. We have been over all of Lake St Clair, Lake Huron, Georgian Bay, Most of Lake Michigan, Green Bay and Lake Erie. This year alone, we made three trips into Lake Erie and two into Lake Huron.

I have dozens and dozens of charts covering Lakes Erie, Huron, Michigan, Georgian Bay, Green Bay and St Clair. Many of these charts are Canadian charts. I have every blow up of every harbor of every lake. After checking every one of my charts, I do not own a single chart that has the units of nautical mile except for a chart I bought last year for the western end of Lake Erie. To this day, the latest Lake St Clair and Lake Huron chart at NOAA still do not have nautical mile as a scale, even though the newest update was Feb 2011.

Lake St Clair: Chart 14850
Lake Huron: Chart 14860

My charts are mostly 1980 to 1995. I have two charts from 1962 that are from early years on my dad’s boat.

The only Mercator projection chart I own is of Lake Michigan. So it requires no nautical mile scale. However, this chart has statute mile, meters and yard scales. This chart I do not use for navigation as I have smaller scale partial charts that show more detail and are much more useful. All these charts are polyconic projection charts, which have only Statute mile no nautical mile.

Interestingly enough, Superior, Michigan, Erie and Ontario are now Mercator Projection charts. Lake Huron is still a polyconic projection chart. The Lake Erie chart I own is Polyconic, not Mercator. So sometime in the last 20 years, Lake Erie was converted to Mercator.

Much of our boating is in Lake St Clair and the bays. It now seems apparent why I have never used nautical miles. I don’t have any charts that I use that have nautical mile as a unit of measure. I have one chart that I could use nautical mile (Lake Michigan) because it is Mercator Projection chart, if I ever used the chart.

Given that my charts that I use are all Statute mile, and given that they are all polyconic projection charts, it is clear why I use the Statute Mile. Nautical mile just makes no sense. It would be like insisting on driving my car based on nautical miles even though every distance sign and map is in statute miles.
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Last edited by BryceGTX; 09-20-2011 at 05:54 AM.
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