Old Boater - Switching to Statute Miles/MPH vs Knots/Nautical Miles???

[Lazy Daze]

So, a nautical mile at the North and South poles is zero in length??
I seem to remember it is consistently one minute at the equator. But, It's been years, like 40, since the schooling....

You were correct in that a nautical mile is based on latitude. But I think you've got longitude on your mind? Longitudinal lines travel N/S, latitudinal lines travel E/W. Lat lines are like rungs of a ladder - the shape of the ladder can change from top to bottom (wide at the bottom, narrow at the top), but the distance between the rungs doesn't change.

However, at the equator, longitudinal lines are ALSO spaced such that a degree equals about 60 N miles... and a second would then be 1 mile. I bet that's what you're thinking of?

 

[Blueone]

You were correct in that a nautical mile is based on latitude. But I think you've got longitude on your mind? Longitudinal lines travel N/S, latitudinal lines travel E/W. Lat lines are like rungs of a ladder - the shape of the ladder can change from top to bottom (wide at the bottom, narrow at the top), but the distance between the rungs doesn't change.

See right there it’s getting to complicated….. mph and miles is just fine

 

[Lazy Daze]

See right there it’s getting to complicated….. mph and miles is just fine

 

[Jaybeaux]

And now a word from our sponsor.....

 

[Skybolt]

Except for the fact that one nm equals one minute of latitude, who cares these days, unless you are using paper charts to navigate.

 

[ttmott]

And 10 MPH (statute miles per hour) equals 8.7 knots (nautical mile per hour) which equals 16.1 KPH which equals 26,880 furlongs per fortnight which equals 0.0000000017578002 AU's per hour.

it's important to know these things.......

 

[ranger58sb]

Except for the fact that one nm equals one minute of latitude, who cares these days, unless you are using paper charts to navigate.

1 NM is 1 minute of latitude on electronic charts, too.



-Chris

 

[Skybolt]

1 NM is 1 minute of latitude on electronic charts, too.



-Chris

Yes it is, but with MFD's the data is automatically calculated and displayed while your measuring or plotting a course. I have yet to see paper charts be able to do that.

 

[Stee6043]

Chartplotting is that neat party trick the super nerds talk about. If the world is ending and the satellites go dark, you might as well scuttle the ship anyway, it's over

 

[Skybolt]

Here's a better one that confuses or boggles me. Where did the term Knot come from? It is from 17th/18th century ship captains who tied knots in a rope at intervals (fathoms?) with a triangle piece of wood at the end and how many "knots" were dragged out of the water is how fast you were going over a given period of time measured by an hour glass.
- How the hell did they know the math for all of this that would later be translated into one nautical mile equals one minute of latitude - or did we just fudge the numbers to make it fit?

Can't really fudge math though can you.

 

[Yendor]

I wasn't going to post this much math, but after ttmot's last post, this is pretty simple:

__ MPH /6000*5280 = KNT ___ or ___ KNT /5280*6000 = MPH _____

 

[ttmott]

Here's a better one that confuses or boggles me. Where did the term Knot come from? It is from 17th/18th century ship captains who tied knots in a rope at intervals (fathoms?) with a triangle piece of wood at the end and how many "knots" were dragged out of the water is how fast you were going over a given period of time measured by an hour glass.
- How the hell did they know the math for all of this that would later be translated into one nautical mile equals one minute of latitude - or did we just fudge the numbers to make it fit?

Can't really fudge math though can you.

From what I recollect - It was knots on a rope tied in equal spans with a piece of wood at the end. Thrown overboard the drag from the wood and knot count per the ships chronometer was the speed.

 

[Skybolt]

From what I recollect - It was knots on a rope tied in equal spans with a piece of wood at the end. Thrown overboard the drag from the wood and knot count per the ships chronometer was the speed.

Isn't that what I just posted, that you quoted?

 

[Skybolt]

I wasn't going to post this much math, but after ttmot's last post, this is pretty simple:

__ MPH /6000*5280 = KNT ___ or ___ KNT /5280*6000 = MPH _____

View attachment 158494

Actually 1 knot equals 1.15078 mph.

 

[Maybe A Dancer]

I always round up to 1.151 - makes my numbers look better !

BEST !

RWS

 

[alnav]

I wasn't going to post this much math, but after ttmot's last post, this is pretty simple:

__ MPH /6000*5280 = KNT ___ or ___ KNT /5280*6000 = MPH _____

View attachment 158495

Although 6000 feet per nautical mile is accepted shorthand, the actual value is 6076.12 feet, so your math will be closer to spot on if you use that number.