USNA Short Course: Chapter Three - 6 Mile Rule

[Down2TheC]

This is the simplest of them all and very handy for not looking to the GPS every 5 minutes.

6 minutes is 1/10th of and hour. So in 6 minutes your travel 1/10th of your speed in distance. Not handy at all unless you convert to yds. (again, we're using 2000yds - 1 NM.)

Doing 5 kts, so it 6 minutes we'll travel 1000 yds. (5 x 2000 = 10000 / 10 = 1000.)
So to skip the math, here's the rule.

Six Minute Rule: Speed in kts * 2, then add two zeros (shift the decimal two places) and you have the yards you'll travel.
8kts will be 1600 yds in 6 min.
3 kts will be 600 yds.
4.6 kts will be 460 yds.

Even easier is if you need to keep it in miles you're just moving the decimal.
6 kts will be .6NM in 6 min

Three minute rule is the same but don't double the number. Just shift the decimal 2 places.
5kts = 500yds in 3 min.
4.5kts = 450 yds in 3 min.

Example: You're 3.2 miles from your harbor, you're doing 5 kts. Your wife wants to know "are we there yet". What's your reply?

3.2 miles at .5 NM each 6 minutes. 3.2/.5 is about 6 and a little bit (remember we're doing quick brain calculations here) 6*6 = 36 min.... say about 38 min.

or

3.2 miles = 6400 yds. 5kts means 1000 yds in 6 min, 500 yds in 3 min. So 6 six mins, and a little less than 1 three min. So just under 39 min.

[Pelagic]

Originally Posted by Down2TheC

Example: You're 3.2 miles from your harbor, you're doing 5 kts. Your wife wants to know "are we there yet". What's your reply?

My reply is quite simple....no math needed...."Yes!"

[SkiprJohn]

Down to the Sea,
Thanks. I'll study that one for awhile and see if I can figure it out.
Regards,
JohnL

[TaoJones]

Originally Posted by Down2TheC

Doing 5 kts, so it 6 minutes we'll travel 1000 yds. (5 x 2000 = 10000 / 10 = 1000.)
So to skip the math, here's the rule.

Six Minute Rule: Speed in kts * 2, then add two zeros (shift the decimal two places) and you have the yards you'll travel.
8kts will be 1600 yds in 6 min.
3 kts will be 600 yds.
4.6 kts will be 460 yds.

Little mistake in that last calculation, D2tC. You've increased your speed by more than 50%, from 3 kts. to 4.6 kts., but you give a distance traveled that's 140 yds. less (600 yds. down to 460 yds.)

The correct value, given your method of calculating this, would be 920 yds. (You skipped the x2 step.)

TaoJones

[Down2TheC]

True, but I can no longer edit it to fix. Besides, any numbers like that it's easiest to stick to miles. 4.6kts - .46 miles in 6 min. Really no need to discuss yards in the 6 minute rule. Don't know why I started with yards (I wrote that 2 years ago and just pasted w/o reading)

[David M]

All navigatiors should know the six minute rule. Its as basic as knowing latitude from longitude.

Another nice trick for doing mental math is to know that there are 2000 yards to a nautical mile. Not exactly, but close enough.

The same goes for 1 meter/second being closely equal to 2 knots.

I get asked by people how fast is a knot? 1.15 MPH. It's easy to remember. Calculate it the same way you mentally calculate a 15% tip in a restaurant.

[TaoJones]

Originally Posted by David M

I get asked by people how fast is a knot? 1.15 MPH. Easy to remember. Calculate it the say way you calculate a 15% tip in a restaurant.

Uh-oh . . . I calculate a 15% tip by doubling the sales tax and rounding up.

TaoJones

[Hud3]

6 and 10 are two very handy numbers. If you change your course by 6 degrees, you'll be off the original course by one mile after traveling ten.

[David M]

Originally Posted by TaoJones

Uh-oh . . . I calculate a 15% tip by doubling the sales tax and rounding up.

TaoJones

You are a generous man Tao! The sales tax in a lot of counties, at least in my parts, are up close to 10% now.

[Down2TheC]

I knew some of you salty dogs would know this stuff.
Hud, see Chapt 2: Radian rule. You're spot on.

[TaoJones]

Originally Posted by David M

You are a generous man Tao! The sales tax in a lot of counties, at least in my parts, are up close to 10% now.

Yeah, that's a good point David - OK, from now on I'll round down.

TaoJones

[SkiprJohn]

Ok Michael. Please revise your first post so that I might understand it with Tao's input.
Kind regards,
JohnL