Knot v mph

[chappy]

Watching the london boat show on tv the other day they had a windsurfer going at a speed of 44 knots & they said this is about 50mph, correct me if i am wrong but i thought the nautical mile is 1852 m which is slightly longer than a standard mile so my calculations are that if you do 1 knot in an hour it should be quicker than doing 1 mph because you are travelling slightly further doing the 1 nautical mile in that hour, am i wrong in my thinking?

 

[BlueSkyNick]

Yes you are wrong in your thinking.

You are right to say that doing 1 knot should be quicker than doing 1 mph, so you only need to be doing 44 knots to travel at the same speed as 50mph (ish), to cover the same distance in the same time.

Easy innit?

 

[chappy]

Thanks bignick, i had a bit of a mental storm.
I should stop these late nights!!!!

 

[DavidGrieves]

Sorry to be the one to point it out, but you are wrong.

44 N,Mile X 1852m = 81.488 Km ie you would have traveled 81Km in an hour.
Now convert your 81Km to Miles(1760yrds), one Km is 5/8 of a mile, so (81 x 5) divide by 8 = 50.93 ie he has traveled 50 statute miles in an hour.
Yeah, I know, "nobody likes a smart arse..."

 

[alienzdive]

The word "knot" means "nautical miles per hour"
This means that when you say "Knots per hour"
You are in fact saying "Nautical miles per hour per hour"
Just "Knots" is fine!!

 

[jimi]

If you do one knot per hour from a standing start then your average speed in the first hour will be 0.5Knots, whereas 1mph will have an average speed of 1 mph so at the end of 108 minutes (approx) the guy travelling at 1knot/hour will have travelled the sane distance as Bignick travelling at a constant rate of 1mph

 

[tcm]

hm, but if you were doing 1 knot from a standing start or a flying start it would stand to reason that you would have done a nautical mile in an hour otherwsie you wouldn't be doing 1knot, unless of course you were travelling at a rate of 1 knot per houi which means you'd be accelerating and at the end of the hour you'd be doing 2 knots.

 

[longjohnsadler]

Equally, 88 feet per second is equivalemt to 60 mph and e=mc2.
Hope this helps

 

[jimi]

Ah no cos 1 Nm/hr = 1 kn so 1kn/Hr = 1Nm/Hr squared which measures the rate of acceleration so at the end of 1 hour you would be travelleing at a rate of 1kn but at the start you would be travelling at 0 knot so the average speed in the first hr = 0.5kn with the distane travelled = 0.5Nm

 

[ChrisE]

Fer God's sake go to bed, I'm losing the will to live, reading this topic.

 

[Shakey]

My fellow Forumites,

Are we not men of reason and learning? Doesn't education, logical thinking, the application of calculus methodologies and a vaguely remembered formula from a 'Letts Revise' A level maths book inform us that:

s = ut + 1/2 at squared. (Read as "s equals u t plus a half a t squared")

where s = distance travelled

u = initial velocity

a = acceleration

t = time

Can someone else work it out please, I can't be arsed.

 

[npf1]

just to complicate things, a nautical mile is the distance projected on the surface by an angle. But the world isn't a perfect sphere so the distance projected in linear terms will differ depending where on the globe you are. So all of the above would need the caveat of "depends where you are"!!!

 

[BlueSkyNick]

Sorry to be the one to point it out, but your are wrong too.

1km is not 5/8 of mile, which is 0.6. It is actually 0.62. Can't be arsed to do the sums properly now, but this would actually make the result even more than 50mph but who cares!

 

[ChrisE]

Nick,
Go to bed, you need your sleep, whilst you've been banging on about this I've managed to put all of my washing in the machine, review a book for the CA, check how Ellen and Mike Golding are getting on and drink a cup of tea and a glass of wine. I'm now off to wind up the mobos.

 

[Wiggo]

Yes, you're are violently agreeing with the TV, through somewhat suspect logic. Anyway, sod converting to metres, just multiply knots by 1.1515 to get mph.

 

[chappy]

COR BLIMEY, i picked some subject there didn't i!!!

 

[Guest]

Actual calc = 44kts as per abitrary number - not cahrt based = 50.634mph

So you are right that 1 kt is quicker than 1mph .... so actually your post is a little confusing .....

 

[Guest]

Re: Knot v mph - why bring in Km\'s

What a load of twaddle .... why bring in Kilometres when they are totally different and irrelevant ?????

there are many free conversion progs on the net that do straight knots to mph, as well as nautical mile to statute miles etc. etc.

And anyway 50.9x is wrong - as you have two errors from rounding due to converting more times than necessary - real answer is 50.634mph

Yeh - you're right - no-one likes a smart-arse ---------

 

[Guest]

But Chart ios one thing .... calculation is another

The calculation other than any that uses spherical trig - ie sights etc. uses an abirtrary figure for the nautical mile ...

Now let me complicate this even further by saying that Radar brings in another Nautical mile standard - 2000m - boffins decided that despite the use of computers and other electronic wizardry to have radar calculate distance based on 2000m for a mile ................

Yep - Time for bed said zebedee

 

[Its_Only_Money]

44Kts = mach 0.06829

Hope this helps! /forums/images/graemlins/laugh.gif