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Haversine Calculator
Someone asked for an easy way to figure out how fast Skip was traveling.
Well I found a nice little on-line Haversine (the function to compute the Great Circle distance between two points) calculator. http://www.movable-type.co.uk/scripts/latlong.html Just input the coordinates from two of Skips messages that are one hour apart and out pops the distance in km. You can do a bit of conversion from there. From Skips' 1257 abd 1357 points he only traveled 10Kms, about 6nm. Cheers Marty |
Haversine Calculator
On Sun, 05 Oct 2008 14:23:08 -0400, Marty wrote:
Someone asked for an easy way to figure out how fast Skip was traveling. Well I found a nice little on-line Haversine (the function to compute the Great Circle distance between two points) calculator. http://www.movable-type.co.uk/scripts/latlong.html Just input the coordinates from two of Skips messages that are one hour apart and out pops the distance in km. You can do a bit of conversion from there. From Skips' 1257 abd 1357 points he only traveled 10Kms, about 6nm. Cool, good find. Here's another site that uses a more convenient (for SPOT data) input format, and returns nautical miles: http://jan.ucc.nau.edu/~cvm/latlongdist.html Here's an example from 3:47PM to 5:47PM where they covered 8 nautical miles in two hours for a VMG of 4 kts. That's not all that bad considering that they are probably under sail with a knot or two of Gulf Sream current against them. Looks like they're heading for the cut through channel in the middle of Frying Pan (Cape Fear) Shoals. Distance Calculation Results Distance between 33.9459N 77.1566W and 33.9139N 77.3133W is 8.0482 nautical miles Source Latitude : 33.9459N Longitude: 77.1566W Destination Latitude : 33.9139N Longitude: 77.3133W Units for results nautical miles |
Haversine Calculator
"Wayne.B" wrote in message ... On Sun, 05 Oct 2008 14:23:08 -0400, Marty wrote: Someone asked for an easy way to figure out how fast Skip was traveling. Well I found a nice little on-line Haversine (the function to compute the Great Circle distance between two points) calculator. http://www.movable-type.co.uk/scripts/latlong.html Just input the coordinates from two of Skips messages that are one hour apart and out pops the distance in km. You can do a bit of conversion from there. From Skips' 1257 abd 1357 points he only traveled 10Kms, about 6nm. Cool, good find. Here's another site that uses a more convenient (for SPOT data) input format, and returns nautical miles: http://jan.ucc.nau.edu/~cvm/latlongdist.html Here's an example from 3:47PM to 5:47PM where they covered 8 nautical miles in two hours for a VMG of 4 kts. That's not all that bad considering that they are probably under sail with a knot or two of Gulf Sream current against them. Looks like they're heading for the cut through channel in the middle of Frying Pan (Cape Fear) Shoals. snip Skippy would be better off going around Cape Fear with plenty of offing rather than trying that yacht channel at night. It appears the winds are nothing to be concerned about so the seas can't bee too bad. The only advantage of transiting the shoal water through the channel might be a little less current but depending upon the state of the tide there could even be more current in the cut than going around the Frying Pan shoals. I'd go outside at night and inside during the day. Wilbur Hubbard |
Haversine Calculator
Wayne.B wrote:
On Sun, 05 Oct 2008 14:23:08 -0400, Marty wrote: Someone asked for an easy way to figure out how fast Skip was traveling. Well I found a nice little on-line Haversine (the function to compute the Great Circle distance between two points) calculator. http://www.movable-type.co.uk/scripts/latlong.html Just input the coordinates from two of Skips messages that are one hour apart and out pops the distance in km. You can do a bit of conversion from there. From Skips' 1257 abd 1357 points he only traveled 10Kms, about 6nm. Cool, good find. Here's another site that uses a more convenient (for SPOT data) input format, and returns nautical miles: http://jan.ucc.nau.edu/~cvm/latlongdist.html Here's an example from 3:47PM to 5:47PM where they covered 8 nautical miles in two hours for a VMG of 4 kts. That's not all that bad considering that they are probably under sail with a knot or two of Gulf Sream current against them. Looks like they're heading for the cut through channel in the middle of Frying Pan (Cape Fear) Shoals. Distance Calculation Results Distance between 33.9459N 77.1566W and 33.9139N 77.3133W is 8.0482 nautical miles Source Latitude : 33.9459N Longitude: 77.1566W Destination Latitude : 33.9139N Longitude: 77.3133W Units for results nautical miles Thanks Wayne, the one I posted lets you use decimal degrees, the only thing is the return in KMs, just divide by 1.85 and you get nautical miles. I put Skip's numbers in for a 12 hour period and got 60nm, not to bad at all, 120 mile days are nothing to be sneered at. Cheers Marty |
Haversine Calculator
Wilbur Hubbard wrote:
snip Skippy would be better off going around Cape Fear with plenty of offing rather than trying that yacht channel at night. It appears the winds are nothing to be concerned about so the seas can't bee too bad. The only advantage of transiting the shoal water through the channel might be a little less current but depending upon the state of the tide there could even be more current in the cut than going around the Frying Pan shoals. I'd go outside at night and inside during the day. I will defer to your local, (perhaps loco?) knowledge. Given modern nav systems though, I really don't see to much issue with doing it at night, tidal currents and those due the Gulf Stream would take precedence for me. Cheers Marty Wilbur Hubbard |
Haversine Calculator
"Marty" wrote in message ... Wilbur Hubbard wrote: snip Skippy would be better off going around Cape Fear with plenty of offing rather than trying that yacht channel at night. It appears the winds are nothing to be concerned about so the seas can't bee too bad. The only advantage of transiting the shoal water through the channel might be a little less current but depending upon the state of the tide there could even be more current in the cut than going around the Frying Pan shoals. I'd go outside at night and inside during the day. I will defer to your local, (perhaps loco?) knowledge. Given modern nav systems though, I really don't see to much issue with doing it at night, tidal currents and those due the Gulf Stream would take precedence for me. I refuse to take a chance, ever, on going aground when there's a safe, viable alternative to taking the chance. One would never wish to go aground on the Cape Fear shoals. It could cost you your boat. Not that they are hard or rocky or anything like that but there's currents and tides thunder storms and not much civilization or assistance around. Wilbur Hubbard |
Haversine Calculator
On Sun, 5 Oct 2008 19:05:53 -0400, "Wilbur Hubbard"
wrote: One would never wish to go aground on the Cape Fear shoals. It could cost you your boat. Not that they are hard or rocky or anything like that but there's currents and tides thunder storms and not much civilization or assistance around. That's all true but the channel is well marked with a couple of large buoys that are exactly where the chart shows them to be. We've been through there twice at night and had no problem. Adverse current inside is about half that of going around the end, it's about 20 miles shorter, and they've got nearly perfect weather tonight. Winds are aft from the NE at 10 to 12 and seas are less than 3 ft, about as good as it gets. I'd definitely go outside in high winds or adverse visibility however. |
Haversine Calculator
On Sun, 05 Oct 2008 18:54:41 -0400, Marty wrote:
I put Skip's numbers in for a 12 hour period and got 60nm, not to bad at all, 120 mile days are nothing to be sneered at. I agree. It's a big heavy cruising boat that is not exactly over rigged, and they have been in light to moderate winds for the most part. |
Haversine Calculator
Wilbur Hubbard wrote:
I refuse to take a chance, ever, on going aground when there's a safe, viable alternative to taking the chance. One would never wish to go aground on the Cape Fear shoals. It could cost you your boat. Not that they are hard or rocky or anything like that but there's currents and tides thunder storms and not much civilization or assistance around. It may be premature to decide where he's going, it'd still be just a small change to port to go SE of the yacht channel, the chart I'm looking at, 11520 seems to indicate he could expect six to eight fathoms there. Cheers Martin Wilbur Hubbard |
Haversine Calculator
Wayne.B wrote:
On Sun, 5 Oct 2008 19:05:53 -0400, "Wilbur Hubbard" wrote: One would never wish to go aground on the Cape Fear shoals. It could cost you your boat. Not that they are hard or rocky or anything like that but there's currents and tides thunder storms and not much civilization or assistance around. That's all true but the channel is well marked with a couple of large buoys that are exactly where the chart shows them to be. We've been through there twice at night and had no problem. Adverse current inside is about half that of going around the end, it's about 20 miles shorter, and they've got nearly perfect weather tonight. Winds are aft from the NE at 10 to 12 and seas are less than 3 ft, about as good as it gets. I'd definitely go outside in high winds or adverse visibility however. Looking his last data, I'm thinking he may be planning to go just inside R12, 18 miles SE of the channel. Cheers Marty |
Haversine Calculator
Wayne.B wrote:
On Sun, 05 Oct 2008 18:54:41 -0400, Marty wrote: I put Skip's numbers in for a 12 hour period and got 60nm, not to bad at all, 120 mile days are nothing to be sneered at. I agree. It's a big heavy cruising boat that is not exactly over rigged, and they have been in light to moderate winds for the most part. I'm pulling for Skip, a few thought he was nuts for attempting this in one leg and warned of dire consequences rounding Cape Hatteras. So far it looks great, except for a chance of getting rained on going into Miami. Cheers Martin |
Haversine Calculator
On Sun, 05 Oct 2008 22:02:17 -0400, Marty wrote:
I'm pulling for Skip, a few thought he was nuts for attempting this in one leg and warned of dire consequences rounding Cape Hatteras. So far it looks great, except for a chance of getting rained on going into Miami. Yes but there were, and still are, some risks: The Gulf Stream off Cape Hatteras is notorious for unforecasted squalls and steep squirrelly seas due to the shoaling water, strong currents and convergant weather systems. They lucked out on that one. I know quite a few very experienced, knowledgeable people who will not go outside Hatteras if they have a choice. I also know a few who swear they will never do it again. One is a friend of mine who had a 56 ft ketch and broke a rudder out there in a storm some years ago. He had to be towed several hundred miles into Norfolk in very gnarly conditions. The next issue in my mind is that they are pushing the limits of mental and physical endurance after many days of round the clock sailing and watch standing. Lots of other people have done that sort of thing successfully, but they are not kids anymore, and the boat is big enough to be a handful if conditions deteriorate or gear starts failing. Last but not least they are heading into southern waters with another 3 weeks to go on the hurricane season. Fortunately storm formation is in a lull and will quite likely continue that way with any luck. I'm reminded of the saying that airplane pilots have: "There are old pilots, and there are bold pilots, but there are no old bold pilots." |
Haversine Calculator
"Wayne.B" wrote
Yes but there were, and still are, some risks: I had dinner last night with the research vessel captain & mate who have about 50 years experience in the waters of Chesapeak Bay and offshore around the capes. I told them what S&L are up to and they said "They've got more courage than we do. I hope they don't make a habit of it." I'm reminded of the saying that airplane pilots have: "There are old pilots, and there are bold pilots, but there are no old bold pilots." The much discussed corollary to that is that taking weather risks and getting away with it tends to effect future judgement. They pulled this off but I too hope they don't make a habit of it. If someone with years of experience had done it, I would be thinking, "Good weather call." but it looks different for a second offshore passage. Roger |
Haversine Calculator
Roger Long wrote:
"Wayne.B" wrote Yes but there were, and still are, some risks: I had dinner last night with the research vessel captain & mate who have about 50 years experience in the waters of Chesapeak Bay and offshore around the capes. I told them what S&L are up to and they said "They've got more courage than we do. I hope they don't make a habit of it." I'm reminded of the saying that airplane pilots have: "There are old pilots, and there are bold pilots, but there are no old bold pilots." The much discussed corollary to that is that taking weather risks and getting away with it tends to effect future judgement. They pulled this off but I too hope they don't make a habit of it. If someone with years of experience had done it, I would be thinking, "Good weather call." but it looks different for a second offshore passage. Roger Don't forget they are using a professional weather router to guide and advise them. Gordon |
Haversine Calculator
Gordon wrote:
Roger Long wrote: "Wayne.B" wrote Yes but there were, and still are, some risks: I had dinner last night with the research vessel captain & mate who have about 50 years experience in the waters of Chesapeak Bay and offshore around the capes. I told them what S&L are up to and they said "They've got more courage than we do. I hope they don't make a habit of it." I'm reminded of the saying that airplane pilots have: "There are old pilots, and there are bold pilots, but there are no old bold pilots." The much discussed corollary to that is that taking weather risks and getting away with it tends to effect future judgement. They pulled this off but I too hope they don't make a habit of it. If someone with years of experience had done it, I would be thinking, "Good weather call." but it looks different for a second offshore passage. Roger Don't forget they are using a professional weather router to guide and advise them. Gordon Well, it looks like they are going to duck into Charleston and wait out the nasty stuff slated for Miami. Maybe they/re getting tired? Cheers Martin |
Haversine Calculator
On Mon, 6 Oct 2008 06:37:49 -0400, "Roger Long"
wrote: If someone with years of experience had done it, I would be thinking, "Good weather call." but it looks different for a second offshore passage. There are places along the beaches of the Outer Banks where you can look out from the sand and see the wreakage of rather large boats that got it wrong for one reason or another. |
Haversine Calculator
On Mon, 06 Oct 2008 12:00:58 -0400, Martin Baxter
wrote: Well, it looks like they are going to duck into Charleston and wait out the nasty stuff slated for Miami. Maybe they/re getting tired? That, and their cat (Portia) got sea sick and peed all over everything. Cute cat, bad behavior. It would be a good call though. Four straight days of good weather is about all you can hope for this time of year. |
Haversine Calculator
On Mon, 06 Oct 2008 12:28:37 -0400, Wayne.B
wrote: On Mon, 06 Oct 2008 12:00:58 -0400, Martin Baxter wrote: Well, it looks like they are going to duck into Charleston and wait out the nasty stuff slated for Miami. Maybe they/re getting tired? That, and their cat (Portia) got sea sick and peed all over everything. I would do the same with those two. Cute cat, bad behavior. It would be a good call though. Four straight days of good weather is about all you can hope for this time of year. |
Haversine Calculator
"Gordon" wrote
Don't forget they are using a professional weather router to guide and advise them. Yes, but the professional oceanographic vessel officers I was talking to get pretty good info as well. -- Roger Long |
Haversine Calculator
On 2008-10-06 06:37:49 -0400, "Roger Long" said:
"Wayne.B" wrote Yes but there were, and still are, some risks: I had dinner last night with the research vessel captain & mate who have about 50 years experience in the waters of Chesapeake Bay and offshore around the capes. I told them what S&L are up to and they said "They've got more courage than we do. I hope they don't make a habit of it." I'm reminded of the saying that airplane pilots have: "There are old pilots, and there are bold pilots, but there are no old bold pilots." The much discussed corollary to that is that taking weather risks and getting away with it tends to affect future judgement. They pulled this off but I too hope they don't make a habit of it. If someone with years of experience had done it, I would be thinking, "Good weather call." but it looks different for a second offshore passage. As one who counseled them that Hattaras could blow up unpredictably in any given hour, particularly this time of year, I have to say it seems they're taking appropriate actions and precautions, are using every available input. They're staying enough clear that they could heave to for many hours, seem to think it might be a nice change. They motor-sailed for 50+ hours to take advantage of the existing conditions vs what was predicted to be on the horizon. They're now obviously heading towards Charleston to ride out expected nastiness -- and probably to take on a bit more fuel. -- Jere Lull Xan-à-Deux -- Tanzer 28 #4 out of Tolchester, MD Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/ Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/ |
Haversine Calculator
"Jere Lull" wrote in message news:2008100619140616807-jerelull@maccom... On 2008-10-06 06:37:49 -0400, "Roger Long" said: "Wayne.B" wrote Yes but there were, and still are, some risks: I had dinner last night with the research vessel captain & mate who have about 50 years experience in the waters of Chesapeake Bay and offshore around the capes. I told them what S&L are up to and they said "They've got more courage than we do. I hope they don't make a habit of it." I'm reminded of the saying that airplane pilots have: "There are old pilots, and there are bold pilots, but there are no old bold pilots." The much discussed corollary to that is that taking weather risks and getting away with it tends to affect future judgement. They pulled this off but I too hope they don't make a habit of it. If someone with years of experience had done it, I would be thinking, "Good weather call." but it looks different for a second offshore passage. As one who counseled them that Hattaras could blow up unpredictably in any given hour, particularly this time of year, I have to say it seems they're taking appropriate actions and precautions, are using every available input. They're staying enough clear that they could heave to for many hours, seem to think it might be a nice change. They motor-sailed for 50+ hours to take advantage of the existing conditions vs what was predicted to be on the horizon. They're now obviously heading towards Charleston to ride out expected nastiness -- and probably to take on a bit more fuel. They aren't real sailors or they wouldn't rely on their diesel so much. They left when they should have known they would have to do a lot of motor sailing because of the light winds mostly from astern. Plus, they're bucking a Gulf Stream current whether they know it or not. I warned them they should have gone the Bermuda route but, noooooooo. Their priorities were to get to Miami to meet some friends there. So they compromised on their ability to sail by leaving in light wind conditions. Real sailors put sailing over meeting friends on a schedule and would have left when a nor'wester was in the offing and rode the damned thing all the way to mid-Florida. Winds from the northwest, even when strong, since they're blowing offshore don't get a chance to heap up the waters very much. Staying close inshore under those conditions makes for a very fast passage with no need to ever run a stupid engine. Wilbur Hubbard |
Haversine Calculator
On Mon, 6 Oct 2008 19:27:31 -0400, "Wilbur Hubbard"
wrote: I warned them they should have gone the Bermuda route but, noooooooo. That's fine if you're going to the islands but I don't know anyone who goes to Florida that way. |
Haversine Calculator
"Wayne.B" wrote in message ... On Mon, 6 Oct 2008 19:27:31 -0400, "Wilbur Hubbard" wrote: I warned them they should have gone the Bermuda route but, noooooooo. That's fine if you're going to the islands but I don't know anyone who goes to Florida that way. True enough but from Miami they plan to go to the Bahamas and the down island if I recall correctly. They've been to Miami already so why go again other than to meet with those friends them mentioned? Or, perhaps they are afraid to go off soundings. From their route they were off soundings only once. And they immediately turned tail and backtracked until they got back onto the continental shelf. They need to overcome their psychological dependence on land. Wilbur Hubbard |
Haversine Calculator
"Jere Lull" wrote
As one who counseled them that Hattaras could blow up unpredictably in any given hour, particularly this time of year, I have to say it seems they're taking appropriate actions and precautions, are using every available input. I'll agree that they have done it well, this time. As long as it doesn't lead them into thinking they can push their luck a little farther next time, and a little farther the next time it works out, they'll be fine. -- Roger Long |
Haversine Calculator
On 2008-10-06 21:40:49 -0400, "Roger Long" said:
"Jere Lull" wrote As one who counseled them that Hattaras could blow up unpredictably in any given hour, particularly this time of year, I have to say it seems they're taking appropriate actions and precautions, are using every available input. I'll agree that they have done it well, this time. As long as it doesn't lead them into thinking they can push their luck a little farther next time, and a little farther the next time it works out, they'll be fine. Urmmm, isn't that how we all broaden our horizons? A little the first time, bit more next, etc.? I'll agree that their first steps are larger than mine, but within the framework of the passage-making they're doing, they're doing it with more awareness of particularly the weather than most delivery crews have. Because of the time-bind they're in, this leg of their journey is more a delivery than cruising, but they ARE ducking out of the weather. As I type, they just entered Charleston Harbor, probably passed Fort Sumter just about now. It really is kewl to flip the satellite view on at times such as this. -- Jere Lull Xan-à-Deux -- Tanzer 28 #4 out of Tolchester, MD Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/ Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/ |
Haversine Calculator
Jere Lull wrote:
As I type, they just entered Charleston Harbor, probably passed Fort Sumter just about now. It really is kewl to flip the satellite view on at times such as this. Ain't that the truth? Think they're headed for the municipal marina? Cheers Martin |
Haversine Calculator
On Tue, 07 Oct 2008 04:16:16 GMT, Jere Lull wrote:
I'll agree that they have done it well, this time. As long as it doesn't lead them into thinking they can push their luck a little farther next time, and a little farther the next time it works out, they'll be fine. Urmmm, isn't that how we all broaden our horizons? A little the first time, bit more next, etc.? When my kids were teenagers learning how to drive, I used to tell them that one of the key things about becoming a safe driver is to live through your first one or two accidents. Until you've been "caught out" a few times the same thing may apply to boating. |
Haversine Calculator
On 2008-10-07 00:20:33 -0400, Marty said:
Jere Lull wrote: As I type, they just entered Charleston Harbor, probably passed Fort Sumter just about now. It really is kewl to flip the satellite view on at times such as this. Ain't that the truth? Think they're headed for the municipal marina? Well, they seemed to tie up to a dock about 1:40 and haven't moved (appreciably) since. -- Jere Lull Xan-à-Deux -- Tanzer 28 #4 out of Tolchester, MD Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/ Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/ |
Haversine Calculator
"Jere Lull" wrote
Urmmm, isn't that how we all broaden our horizons? A little the first time, bit more next, etc.? This is an issue I gave a lot of thought to during my flying days when people I knew died more frequently than in boating and I was very interested in the human factors because it was clear that they were the primary determinent of longevity. There is a very subtle distinction between developing experience and increasing proficiency and luck. The house odds never change. While increasing competence lets you safely deal with more challenging situations, it's easy to start thinking that this effects the latter. Its killed many pilots as well as sailors. I personally think S&L are doing very well and had a good strategy for this ordinarily risky passage. I don't expect them to get cocky but it's something to think about in general terms. I"m sure they are still making a lot of mistakes but I'm still making them after four decades of sailing. They are making good progress on the basics. I saw them right after their first long passage and they were remarkably perky. They have found a watch keeping and energy conservation routine that works. They have the makings of solidly competent cruisers despite (or perhaps because of) their well publisized early mistakes. -- Roger Long |
Haversine Calculator
On Sun, 05 Oct 2008 14:23:08 -0400, Marty wrote:
Well I found a nice little on-line Haversine (the function to compute the Great Circle distance between two points) calculator. I have had good luck with a pair of deviders. Casady |
Haversine Calculator
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Haversine Calculator
On Oct 8, 10:03*am, Wayne.B wrote:
On Wed, 08 Oct 2008 15:04:51 GMT, (Richard .... I have had good luck with a pair of deviders. .... How do you calculate great circle distances with dividers ? Plot the LL's on a gnomic chart? --Tom. |
Haversine Calculator
On Wed, 8 Oct 2008 10:17:50 -0700 (PDT), "
wrote: On Oct 8, 10:03*am, Wayne.B wrote: On Wed, 08 Oct 2008 15:04:51 GMT, (Richard ... I have had good luck with a pair of deviders. ... How do you calculate great circle distances with dividers ? Plot the LL's on a gnomic chart? That might work as a piece-wise approximation. |
Haversine Calculator
On Oct 8, 9:15*pm, Wayne.B wrote:
On Wed, 8 Oct 2008 10:17:50 -0700 (PDT), " How do you calculate great circle distances with dividers ? Plot the LL's on a gnomic chart? That might work as a piece-wise approximation. Sorry, I know that wasn't a very helpful idea. Since a straight line on a gnomic chart is a great circle if you just count the number of degrees along the line that should provide naut miles. I'm not sure how helpful dividers would be in measuring those degrees. I'm also not sure if they make gnomic charts to a scale appropriate for plotting such short distances. What would be the point? --Tom. |
Haversine Calculator
On Thu, 9 Oct 2008 09:01:39 -0700 (PDT), "
wrote: That might work as a piece-wise approximation. Sorry, I know that wasn't a very helpful idea. Since a straight line on a gnomic chart is a great circle if you just count the number of degrees along the line that should provide naut miles. I'm not sure how helpful dividers would be in measuring those degrees. I'm also not sure if they make gnomic charts to a scale appropriate for plotting such short distances. What would be the point? Good question since it's so easy to do it computationally. Our friend Richard Casady claimed he could do it with dividers but I suspect he hasn't really tried it. The only graphical solution with dividers that I would have much faith in would be on the surface of a globe using a taut string. Everything else I can think of would be a piece-wise approximation using computed way points on a Mercator chart. |
Haversine Calculator
On Oct 9, 10:27*am, Wayne.B wrote:
...*The only graphical solution with dividers that I would have much faith in would be on the surface of a globe using a taut string. ... If you have just the right projection it can be done but you'd need a custom chart which is going to be harder to come by than a programmable calculator. I haven't been following Skip's path closely enough to know, but I suppose he was heading near enough to true south that the rhumb line distance can be taken as the great circle distance with negligible error. In a desperate attempt to add some content I want to point out that if you are going to do sailings calculations by calculator and are looking to Dutton's (at least up the edition 14) for guidance beware that the sailing chapter is full of errors large and small. This is a better source: http://williams.best.vwh.net/avform.htm --Tom. |
Haversine Calculator
On Thu, 9 Oct 2008 11:14:58 -0700 (PDT), "
wrote: In a desperate attempt to add some content I want to point out that if you are going to do sailings calculations by calculator and are looking to Dutton's (at least up the edition 14) for guidance beware that the sailing chapter is full of errors large and small. This is a better source: http://williams.best.vwh.net/avform.htm Good site, thanks. I have a Dutton's somewhere but haven't cracked it in years. I think the Naval Academy used it as a navigation text at one time. :-) |
Haversine Calculator
On Oct 9, 12:12*pm, Wayne.B wrote:
On Thu, 9 Oct 2008 11:14:58 -0700 (PDT), " ...http://williams.best.vwh.net/avform.htm Good site, thanks. I have a Dutton's somewhere but haven't cracked it in years. *I think the Naval Academy used it as a navigation text at one time. * :-) You're welcome. Somebody posted it here a while ago. I'm sorry I've forgotten who, but thanks to them. I have tested most of the algorithms there and they work. I worked all the problems in the Sailings chapter in Dutton's because I wanted to make a Mercator sailings calculator -- GC calcs are a dime a dozen. I was amazed at how bad the text was. I left the book in Hawaii but if my memory serves the algorithm they provide for Mercator sailing is not generalizable and only works in special cases in the NW. The problem they work is so full of errors that even a casual glance shows it to be impossible -- they did crib the answer but all their work is wrong. There were also serious problems with the GC section. This for a book that is still the navigation text at the USNA and has gone through 14 editions... Presumably that means no one at the Academy has bothered to work or even closely read the sailings problems... ... Dutton's does have really nice illustrations... --Tom. --Tom. |
Haversine Calculator
On Thu, 09 Oct 2008 13:27:55 -0400, Wayne.B
wrote: On Thu, 9 Oct 2008 09:01:39 -0700 (PDT), " wrote: That might work as a piece-wise approximation. Sorry, I know that wasn't a very helpful idea. Since a straight line on a gnomic chart is a great circle if you just count the number of degrees along the line that should provide naut miles. I'm not sure how helpful dividers would be in measuring those degrees. I'm also not sure if they make gnomic charts to a scale appropriate for plotting such short distances. What would be the point? Good question since it's so easy to do it computationally. Our friend Richard Casady claimed he could do it with dividers but I suspect he hasn't really tried it. The only graphical solution with dividers that I would have much faith in would be on the surface of a globe using a taut string. Everything else I can think of would be a piece-wise approximation using computed way points on a Mercator chart. You can't possibly think the difference between a 6 mi long rhumb line and a great circle is of any significant. My uncle navigated a few million miles with dividers and charts. I have the dividers, two of them, as a matter of fact. The E6B nav computer has circular slide rule on one side, on the other a slice of a plotting board, for solving wind triangles. I have that one, and another he stole and gave me in 64. There was a sextant built into the plane. You ever hear of a B-52 getting lost? Casady |
Haversine Calculator
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