Re: Great Lakes Boaters, Polyconic charts, mph
Came across this old thread whilst poking around. Looks like an interesting part of the world to sail in - you're lucky!
Polyconic projection is an interesting subject and certainly not something I've come across before, but I thought I'd correct an error in the statements below in case anyone else happened by and came to grief as a result:
Originally Posted by BryceGTX
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
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.
The charts listed above (and presumably most others you own) are all clearly marked in Nautical Miles
along both edges in the standard fashion of nautical charts of every other corner of the globe. NOAA have helpfully added Statute mile scales and a host of other relevant info for you to use if you want to.
Over such a small area of the planet you're free to use miles for your navigation if you want to - but to categorically state that the charts used are in Statute miles and "Nautical mile just makes no sense" simply is not correct.
"Honestly, I don't know why seamen persist in getting wrecked in some of the outlandish places they do, when they can do it in a nice place like Fiji." -- John Caldwell, "Desperate Voyage"
Last edited by Classic30; 10-03-2012 at 11:29 PM.