Speed indicator

[OldCat]

RIck I: No - or Its Changed

A nautical mile is now defined as exactly 1852 meters. It is very close to the average of 1 minute of arc along a great circle of the earth - but is no longer defined as such due to the variances caused by the earth's not being a true sphere.1 minute of arc along a great circle is still accurate enough for most of us to navigate by - but the international definition is 1852 meters (exactly).

 

[Rick I]

charts haven't changed

OldCat,Wow, defining a mile in metres! When and who did this? Checking in Google I found that what you are referring to is the International Nautical Mile. I don't think this can be used in navigation. I have yet to see a chart where 1' of arc on a meridian is constant. Celestial navigation hasn't changed and, as far as I know, a mile is greater as you get into higher latitudes. Just try plotting a sight with plotting sheets that aren't for the proper latitude when great circle sailing and see how accurate you are. Having said this it would be interesting to see how speed is determined on gps units, whether it is distance measured by arc divided by time or distance measured by arc converted to metres divided by time. Knowing nothing about what goes on inside these things I hope someone who does know enlightens us.

 

[Fred Ficarra]

Wow,

This all started with Cheetos!

 

[Dave A.]

Speed over water

There's a thing called a "J" tube which is calibrated in knots. You stick it in the water and read the speed in knots by how high the water rises in the tube. About as simple as you can get after the log and line. I had one when I was into small boats, a Melges M-16, and it was pretty handy. You could probably find one somewhere.Fair Winds,Dave A.S/V Wind SongPearson 35

 

[Eric]

speed and distance

What is really cool, is that the nautical mile is directly related to the amount of time that the Earth takes to revolve one time....It is not related to the time that is takes a Roman solder to walk 1000 paces.Good Winds.Eric

 

[Rick I]

Slow walker

Eric,What if the Roman soldier takes 24 hours to walk 1000 paces?

 

[Fred Ficarra]

Speaking of Romans,

did you guys hear the one about,,, the Space Shuttle and Roman Chariot's? Seriously, I've been looking for the email that spells it out. I have to go by memory so I'll no doubt leave something out but it goes like this;The Shuttle is underpowered because its' booster rockets are built by a company that were awarded a pork barrel contract. (Morton Thiocol, sp) They are located where the rockets can't be built large enough to do the things that the shuttle was originally hoped to do. Seems that a railroad tunnel from the pork barrel plant is too small for a proper sized rocket. The reason it's that size is because of railroad gauge standard in the U.S. that evolved so as to be standardized with England. The reason the English use that size is so the tracks are somehow compatible with the roads. Something to do with cargo, I can't remember. Anyway, the roads were always the same size since they were built. And they were built by the Romans. The width was set because of the spacing of Roman chariot wheels. So the Space Shuttle is lame (among several reasons) because of Roman Chariots 2000 years old.  This one's going around the web for the last year or two so maybe someone can paste it here. I think it's just as cute as Roman paces.

 

[Fred Ficarra]

I googled it, duh,,,

Lots'a suff.

 

[OldCat]

Rick I: Please look at the link . . .

I posted this earlier on in this thread - but it seems to have been missed by many. The info on the 1852 meter definition is there, as is the 1 minute of arc along a great circle of the earth. You can follow links within that link to the SI defining bodies.When a GPS works to nautical miles - I'll bet it works to the international standard.

 

[Tereza]

Minutes of Latitude same everywhere...?

While longitude varies in actual distance covered from eaquator to pole, I believe that latitude is constant from equator to pole.Is that right?

 

[Rick Webb]

Good Story, But It is Just a Story

http://www.snopes.com/history/american/gauge.htm

 

[Didereaux]

responses from people who had lapses of ....

It's absolutely leg slapping hilarious most times, and frustratingly sad the rest to read the nonesense that some people believe about 'hard' science and engineering facts(facts being the 'day to day accepted values)used in those fields. It is quite obvious that they either never were exposed to courses or training(even on the job) OR, and this is most likely for most of the drivel, they were way to busy plotting to get in some girls pants, somebodies keg of beer or how to soup up their junk-mobile.In other words go somewhere OTHER than a goddam BB, blog or newsgroup on the internet to get information that might in some manner affect your general well being(read keep your damned boat afloat and such)Was that a rant???? dammed right it was! gLuk

 

[Stu Jackson]

Try this

It might be interesting to see if there is any relationship between the amount of time or distance that these respondents have sailed their boats more than five miles away from their docks and their understanding of a nautical mile or anything else that's a measure of distance rather than 1660's admiralty law.Sure, it's helpful, but real.........?

 

[BobW]

Terribly sorry, Didero, old chap..........

We're enjoying ourselves here, sharing facts, theories, hypotheses, opinions, and generally just having a good old time Since you are so obviously far more advanced than us in every aspect, just why do you deign to dabble in our lowly affairs?OK, Phil, the wine (a very good, but young, Australian vintage) has overcome my better instincts... you can axe me now and I won't feel the pain!!!Cheers,Bobs/v X SAIL R 8

 

[BobW]

Oldcat, a GPS doesn't work to any

measure of distance, it only gives a position. That's all the satellite system provides, anything else has to be internally generated/interpolated.After Fred's posts of this morning, I googled GPS and learned a lot (I even found a site that had some of the code and algorithms used *yks)What strikes me most from studying GPS and nautical charts is their propensity for error. It's hard to depend on any of them.Cheers,Bob s/v X SAIL R 8

 

[Rick I]

Lighten up

Hey Stu & Didereaux,This is the only entertainment I have. No need to get personal about sailing qualifications or time spent sailing. As for sailing, in summer I sail every weekend (boat's coming out of the water this week). And then I sail and live on my boat from November to June, mostly in the Bahamas.

 

[Stu Jackson]

What's wrong with "plotting?"

Gee, Rick, we're only having fun, too. C'mon...Stu

 

[b393capt]

Three Cheers for Rick

I have followed Rick I's post on three different boards, over 100 posts I have read myself (sure there are many more) and have not found a piece of advise I disagree with.The time he spends on these boards assisting other sailors should be commended.Rick, I personally want to thank you for several bits of advise I had the joy to read, even if they were not addressed directly to me, and in addition I have found great value in the Yahoo group posts for the 393.Well Done !Dan

 

[OldCat]

Bob, Not The Way I Meant It

Bob wrote: "Oldcat, a GPS doesn't work to any measure of distance, it only gives a position. That's all the satellite system provides, anything else has to be internally generated/interpolated."I didn't mean it that way - I wasn't referring to its fundamental measurement - by 'working' I meant all of its internal processes. What I am saying is that the GPS will have 1852 meters = 1 NM or some binary equivalent in other units coded into it. When it calculates a distance or speed - knots or NM, it will work off the international standard.While close - a nautical mile is no longer defined by international standard as 1 minute of arc , but by the 1852 meter = 1NM standard.

 

[BobW]

I couldn't find anything about the inner

workings of a GPS, other than a notation that the satellite signal transmits every 30 seconds. Also, when using a GPS with a chart, it is critical to match up the datum in use, otherwise... well, you won't be where you think you are.If anybody wants a sleepless night, read the book titled 'How to read a Nautical Chart' - hte first part of the book goes into great detail about the innacuracies in charts. *yksCheers,Bobs/v X SAIL R 8