Knots vs MPH

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Sheesh! 5 pages of comments in less that 2 full days. Good thing we aren't talking about anchors!

Anyway, It really boils down to (1) what chart you are using and (2) what you want to use. Your choice and no one else's (despite that they may think).

Marty....................
 
Most of the coastal cruising guides are in statute miles. Statute miles to marinas. Statute miles to bridges. Statute miles to anchorages. I use miles.

Offshore everything is knots/nautical miles. It is rare to use both in the same day so change as necessary. There is no "right" or "wrong" only what works best for you and the situation.
 
bilge53 said:
Most of the coastal cruising guides are in statute miles. Statute miles to marinas. Statute miles to bridges. Statute miles to anchorages. I use miles.

Offshore everything is knots/nautical miles. It is rare to use both in the same day so change as necessary. There is no "right" or "wrong" only what works best for you and the situation.
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Not coastal, intracoastal. The ICW is measured off in statute miles, as are the inland waterways. Here's an always handy reference:

http://www.nauticalcharts.noaa.gov/nsd/distances-ports/distances.pdf
 
Did you knot know what I meant?
 
furlongs per fortnight.. Had a college physics test that used those units. That may be the only thing that I remember from college physics.
 
Cuttyhunk47 said:
To me, anyone who has sold out and changed to knots from cables is not a real mariner. I suppose you measure your depth in feet and not fathoms too!
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Metres (or meters).
 
In every small recreational boat I've owned that had a speedometer, the speedometer indicated statute miles per hour, not knots. So, it's just natural for most boaters who have "moved up" to larger boats to continue to use SM.
 
MrJim said:
In every small recreational boat I've owned that had a speedometer, the speedometer indicated statute miles per hour, not knots. So, it's just natural for most boaters who have "moved up" to larger boats to continue to use SM.
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But in every larger boat I've owned the speedometer or guages read knots. Well, most had choices but read knots when we set them to do so.

You're right about smaller boats such as we had on the lake. Still when we moved to the coast and ocean cruising, we switched to comply with what we felt was the norm for that type boating and location. We also were then around people with much more experience than us, professional captains and others and all used knots.
 
Cuttyhunk47 said:
To me, anyone who has sold out and changed to knots from cables is not a real mariner. I suppose you measure your depth in feet and not fathoms too!
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You just wont believe me If I told you I have a wrist watch with a tiny little battery in it and you cant wind it up :rofl:
 
For those of you doing the math furlongs per fortnight is easily converted to 1 centimeter per minute. As one would use furlongs at the horse track, small vessels usually restricted to use on inland lakes, bays, and waterways would necessarily be equipped with a speed measuring device in MPH as those are the units used on those waterways. Nautical miles and Knots are more readily used in open waters where the charts have lat and long scales.
 
My calculations are normally way off when estimating times to destinations. See signature below :D
 
MurrayM said:
My calculations are normally way off when estimating times to destinations. See signature below :D
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We calculate a range of times and a lot of what-if's. But then we do the same in a car. We don't like traveling in a car but we never know how many stops we'll make or not make. If we see something that interests us or get hungry or just tired, we stop. Boat routes and destinations and calendars are always subject to change.
 
BandB said:
Where it's really a problem and I've run across a couple of boats fall victim to this is where one assumes the 2 is meters or fathom and it is feet. I ran across one who soft grounded and was easily backed off who understood quickly his mistake and took it as a learning experience. I heard the story from him first handed.

The other one was a classic "how not to." This one I heard part on radio (We were docked at Resort World, Bimini), heard the rest from the marina and from a tow captain. First he grounded soft but deep at about 15 knots. Then he tried to power it on through and off, just putting it in worse condition. Next he called asking about towing. He carried no tow membership and was quoted $1000 plus $200 an hour for any time over an hour took removing him from the ground. He ranted and cursed and refused that and had everyone get out of the boat and try pulling it off by hand. As that obviously didn't work it then reached low tide and the boat was in less water. Finally he called back regarding the tow. The towboat arrived. Told him they'd wait for high tide but with what he'd done now it was likely to be a salvage and would cost more. The man proceeded to use every expletive and derogatory term possible against Bahamians. But they did use floats under the edges of the hull to minimize any further damage and took about 4 hours removing it and price went to $2000. The tow captain recommends he go to the marina and get a diver to check things out. The owner says, he wouldn't step foot on the Bahamas if it was the last place on earth and he's turning around and heading straight back to Florida. Now all this was taking place just south of Bimini. That's when he was informed he needed to clear into the Bahamas. A few more expletives and he said no he didn't as he wasn't going to the Bahamas. He was informed he was already in and had been "anchored" in Bahamas waters for 10 hours. He received an escort to Brown's and Alice Town, paid his $300 plus $75 exiting fees and left cursing everyone there.

Now, this last part I only heard as rumor and that was that he failed to clear back into the US and got cited for that.

So, I'd say the first guy suffered from the inconsistency on charts but the second guy more from his own idiocy. I was told by people who observed him at the marina that he was very lucky he was in the Bahamas as his language and behavior toward the Bahamian authorities likely would have gotten him arrested in the US.
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LOL!

The newer Canadian (CHS) charts are in metres and decimetres and the older ones are in fathoms and feet. CE shows the info from the title block which identifies which is which. So does iNavX. As long as the chart shows 3 metres or more, most of us are ok.


Jim
Sent from my iPad using Trawler Forum
 
danderer said:
Sorry for being a bit flippant in my wording. Here is the longer version:

In common usage (Speed Limit, Maximum Speed, etc), "speed" equates with "velocity". Some would argue more strictly that speed is a scalar while velocity is a vector but I don't think that matters here.

Velocity is the first derivative of position and time--the change in position divided by the change in time. Distance/time (eg. miles/hour). A knot is a measure of velocity: 1 nautical mile/hour.
Click to expand...

Your definition of velocity is incorrect
Velocity is a speed and a direction
If your boat is doing 10 mph, this is your boats speed
If your boat is doing 10 mph, NORTH, then the boats velocity would be
stated as 10 mph north.

Therefore your comment " a knot is a measure of velocity" is incorrect

Is this important for a boat or a car for what we are talking about, not really but for navigation purposes it would be more important. Ie
10 mph, or nautical miles per hour, at 192 T degrees gives the boats speed and direction and you could mark this on a chart.
 
On the water you must use nautical mile (1,852m), Knot means nautical miles per hour


Sergio "Alemao" Sztancsa
Sent from my iPhone, using Trawler Forum
 
So, if I get this right, if I am telling someone, especially the USCG, that I am heading northeast at 6 knots , they wont have a clue as to what I am talking about?
They will come back to me and ask my velocity?
There are times when slight mis-usage of the language doesn't mean very much other than being grammatically incorrect, especially in a car where on a winding road.
The only time I ever use the term "velocity" is when referencing "Velocity Made Good" when sailing.

"Nautical miles" are used almost exclusively in open water. On the eastern US inland waterways, and many lakes and other rivers, "Statute Miles" is what you will see on the charts. I set my GPS accordingly.
 
Wifey B: The velocity of this thread is off track at the speed of light....:)
 
Tony B said:
So, if I get this right, if I am telling someone, especially the USCG, that I am heading northeast at 6 knots , they wont have a clue as to what I am talking about?
They will come back to me and ask my velocity?
There are times when slight mis-usage of the language doesn't mean very much other than being grammatically incorrect, especially in a car where on a winding road.
The only time I ever use the term "velocity" is when referencing "Velocity Made Good" when sailing.

"Nautical miles" are used almost exclusively in open water. On the eastern US inland waterways, and many lakes and other rivers, "Statute Miles" is what you will see on the charts. I set my GPS accordingly.
Click to expand...

Not sure who you were referring to, but velocity is not speed, speed is a component of velocity. I doubt any CG would ask for your velocity
On the other hand, they might ask for your speed and heading, which is velocity
We were in Canadian Waters and our course could take us in front of or behind a large ferry in about 10 minutes. The ferry sent a call to us and asked what our speed and heading was as I suspect the navigator wanted us to acknowledge that we saw them. He would have got the speed and heading off his radar.
 
Wifey B: When is the last time anyone used the word "velocity" in normal conversation?

Jane: I'm on my way to your house. I'm at I-95, just crossing Broward.

Jill: What is your velocity?

Jane: Wtf??? My velocity? I don't know. Don't even know if I have it. Speak English girl.

:rofl:
 
BandB said:
Wifey B: When is the last time anyone used the word "velocity" in normal conversation?

Jane: I'm on my way to your house. I'm at I-95, just crossing Broward.

Jill: What is your velocity?

Jane: Wtf??? My velocity? I don't know. Don't even know if I have it. Speak English girl.

:rofl:
Click to expand...

If you have ever done any sailing, VMG (Velocity Made Good) is a very real and useful measure. It used to be on the primary windows of GPS's back when they first came out. I am sure that is on my chartplotter somewhere...I just haven't looked for it.
 
Baker said:
It used to be on the primary windows of GPS's back when they first came out.
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Wifey B: You mean in olden days? ;)

I've sailed but nothing serious so haven't heard or used that term. Still in ordinary conversation it just doesn't come up often. I wonder what percent of the people even know it's meaning. I think most probably think it is just another word for speed...Wrong. Oh well. Climbing back under my chair. Not really. :hide:

Just waiting for lunch. Darn this lake is calm and beeeeeuuuuutiful. Almost glassy. What a change from a few days ago.
 
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Given the precision of my boating navigation, equipment, and weather/tide guesses - the issue of statute/nautical conversion, if ignored, introduces an error of + or - 15% - well within the overall precision and accuracy of the process. At 8 or even 14 knots, plenty of time to make "field adjustments" within these tolerances en route.

My go to is NM, in practice.
 
Don't forget to factor in the gravitational constants g sub c and g sub s where applicable.
 
"Course Made Good" and "Velocity Made Good" are very important to sailors on long passages or long trips. They are not very useful when day sailing or weekending because you usually know where you are anyway.

An example of Velocity made Good is when Crossing an ocean or the Gulf of Mex. Say for instance your destination is 450 miles away. You have to tack because of a strong headwind and seas against you. While tacking, you are going like a bat out of hell at a mind bending speed of 7.5 knots. Now you flip to the screen for "Velocity made Good" and you see that it is only 1.5 knots towards your destination. With a 450 mile destination, you would normally figure out your time by roughly 100 miles a day toward your target. With a velocity made Good of 1.5 knots, you better have A LOT of rum on board.
 
ve·loc·i·ty
vəˈläsədē/
noun​

[COLOR=#878787 !important]
  • the speed of something in a given direction.

[COLOR=#878787 !important]"the velocities of the emitted particles"[/COLOR]​



  • (in general use) speed.

  • [COLOR=#878787 !important]"the tank shot backward at an incredible velocity"[/COLOR]
    synonyms:speed, pace, rate, tempo, momentum, impetus; More​

    [COLOR=#878787 !important][/COLOR]​


    ​
  • ECONOMICS
    the rate at which money changes hands within an economy.​

    ​
  • FIREARMS :
bullet speed


DOMESTICS



Keeping wife happy... how fast the word yes can be uttered.





​
[/COLOR]
 
Last edited:
Art-not responding "Yes" fast enough to your wife is generally called "Terminal Velocity".
 
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