YM Ocean questions

[Fascadale]

Well said

Those who rant that astro nav is dated and no longer relevant only demonstrate ther own lack of experience and understanding of safe navigation. There is currently no back up to GPS when mid ocean other than a sextant and a little knowledge. Having no means of calculating position other than DR when mid ocean is not an acceptable or safe practice.

I entirely agree with these sentiments: I am doing the ocean course so that I can learn the skills of pre electronic navigation.

My question is about the qualifying passage and its definition.

I am slightly confused as to why a North Sea passage of the right length does not qualify because to the number of rigs there from which one could take a bearing. If I wanted to cheat by using "non astro" methods to check my position I could use my GPS as easily in Biscay as in the North Sea. I am unsure of the logic of the objection to the proposed passage.

I am certainly not questioning the value of astro navigation, or its place in the Ocean syllabus.

 

[oldbilbo]

I've long suspected there's more than a handful of eedjits in the RYA Training 'bubble' who 'don't know their zeniths from their apogees'..... but I have a very different view of the several Ocean Examiners I've tripped over along the way. They're independent to the point of eccentricity - but they certainly know their onions!

So, howzabout taking a Departure from the Bell Rock and heading for the bottom end of the Lofotens....? Done in mid-summer, you should have plenty of daylight/time for lots of astro - and there's the intriguing prospect of shooting a 'circumpolar sun'. Whether stars and planets would be available, due to solar illumination, is uncertain. There is the moon, of course.....

Have a read of 'Dutton' here.

 

[prv]

If only he had had a self contained GPS in a tupperware box as back up, he might not have lost his boat.

Make it a tin box, then it might possibly shield against nearby lightning strikes as well

Pete

 

[Fascadale]

Another possibility is going from here

to here

 

[AntarcticPilot]

Remember that a famous member of the Royal Institute of Navigation had to abandon the original Jester because excess water in the cabin had totally ruined his sight reduction tables.

When offered the chance to abandon ship, he felt obliged to take it because without the means to navigate safely, there was no point in trying to repair the damage to the hatch, etc.

If only he had had a self contained GPS in a tupperware box as back up, he might not have lost his boat.

Well, Captain Cook had to calculate his own ephemeris after the 2nd year of the Third Voyage - and that included the Lunar ephemeris, which is far trickier than the other celestial bodies. So, you can manage without tables if you have to - and have the relevant knowledge! And there is at least one sight that doesn't need tables; altitude of Polaris gives latitude near enough (I think you can use the Southern Cross in the southern hemisphere, but it isn't as accurate).

Many, many years ago I did a small surveying exercise while away from civilization. Our stores didn't include either a calculator (horrendously expensive in those days) or tables. I was able to dredge up enough mathematics to calculate sines and cosine to be able to complete the work in hand. I doubt I could do it now - my memory of the relevant series needed to compute sines is long gone!

 

[Roberto]

I was able to dredge up enough mathematics to calculate sines and cosine to be able to complete the work in hand. I doubt I could do it now - my memory of the relevant series needed to compute sines is long gone!

you could print a set of trig tables and then laminate them (I confess I have done it), half an A4 page will keep all angles 0-45°, you can then write the conversion formulas for all the rest of the 360°
No danger of paper getting soaked then

 

[snowleopard]

Don't forget that the 'exam' is an oral where the examiner will check you out on far more than just astro and weather. He'll put you through hoops on vessel preparation, crew selection, passage planning etc.

As he has to re-work your sights to check they are correct, presenting him with a load of extra work will be very unpopular.

 

[oldbilbo]

Don't forget that the 'exam' is an oral where the examiner will check you out on far more than just astro and weather. He'll put you through hoops on vessel preparation, crew selection, passage planning etc.

Fairy 'nuff! 'Anything on the syllabus'..... I took to mean everything from Competent Crew onwards. And so did 'my' guy.

As he has to re-work your sights to check they are correct, presenting him with a load of extra work will be very unpopular.

I'm of the view that he'll only 're-work the sights' sufficient to determine if one is using an OK method and can use it avoiding errors. Surely (s)he'll only dig deep enough to satisfy himself one way or another......?


"Does the candidate know what (s)he's doing here? Can (s)he extract the information with sufficient accuracy? Can (s)he use the information AND the uncertainties with understanding and good judgement?"

Shirley.....?

 

[Fascadale]

So, howzabout taking a Departure from the Bell Rock and heading for the bottom end of the Lofotens....? Done in mid-summer, you should have plenty of daylight/time for lots of astro - and there's the intriguing prospect of shooting a 'circumpolar sun'. Whether stars and planets would be available, due to solar illumination, is uncertain. There is the moon, of course.....

Interestingly and perhaps unfortunately, the Bell Rock to the Lofotens would probably not pass as a "qualifying passage"

Although the overall distance is about 840nms the longest leg of the passage outwith 50nms from the shore is only 240nms. 250nms is the requirement.

There are also a lot of rigs along the course that I am told by the RYA might be used for bearings thus putting the passage outwith the spirit of the event

 

[SteveSarabande]

maybe I am simplifying things a little, but to me an ocean qualifying passage should be on an ocean. Otherwise you could just go 50mile offshore and sail parallel to the coast

 

[AndrewB]

Well, Captain Cook had to calculate his own ephemeris after the 2nd year of the Third Voyage - and that included the Lunar ephemeris, which is far trickier than the other celestial bodies. So, you can manage without tables if you have to - and have the relevant knowledge! And there is at least one sight that doesn't need tables; altitude of Polaris gives latitude near enough (I think you can use the Southern Cross in the southern hemisphere, but it isn't as accurate).

Well yes, there are methods of astro navigation using improvised instruments and tables. Sorry, but it doesn't include the Lunar Ephemeris or the Moons of Jupiter - not aboard a yacht! But this story doesn't ring true. Mike Richie was picked up by a ship. In pre-GPS days, they would have certainly been able to lend him a sextant and tables if that was all that prevented him continuing.

 

[ytd]

I sense a lot of "well we had to do it so any new disciple has to do it" here. My point is that the course time spent on astro would be better spent on things like weather forecasting, crew management, sail trim, engine repair, etc.

I used astro in the 70's because it was the best affordable technology available at the time. I also used fax machines and typing pools. Don't see many of those today. It's accepted that bodies controlling leisure activities such as yachting will place emphasis on heritage activities. Does amateur radio still require morse for a full HF licence? But the comparison with commercial activities would see motor mechanics required to know how to shoe a horse or repair spoked wheels.

And as to all the reasons why failure of 3 GPS is far more likely than clock or radio failure or tables getting wet or sextant being bent. Laughable. And the old chestnut, "what if they turn the GPS off?" If they turn the GPS off I'll be thanking my lucky stars I'm in the middle of an ocean and not in some city waiting for a missile strike or terrorist bomb. Knowing my exact position would be a second order priority. And I would do what I did in the 70's when I hadn't been able to get a sight for a few days in the tropics, approach during daylight hours only keeping a good lookout.

 

[mcframe]

BTW, it is not commonly known that the US astronauts on ill-fated Apollo 13 carried and used a sextant to help establish exactly where/when to initiate an essential 'braking burn'. Without that - and the knowhow - there would most likely have been a 'lost in space' outcome.

<reading>
http://www.universetoday.com/62763/...lo-13-part-6-navigating-by-earths-terminator/
</reading>

I didn't know that - thanks.

More at:
http://fer3.com/arc/m2.aspx/Space-sextants-FrankReed-oct-2010-g14170

 

[Uricanejack]

I have absouloutly no idea who conducts rya exams.

If an examiner does not accept the use of a GPS position as a dr for your sight he or she is out to lunch. your DR could be a position selected by a pin stck in chart. The points they will be looking for are. did you name your intercept correctly.correct azimuth. and apply your corections in the right direction.

More can be deduced about your knowladge by watching you pick up the sextant and check the errors. use your left hand.

turning up with star sights having used a davis done in mid ocean from a small you are a bull****er.

Show up with a regular noon position taken using a GPS dr. Run to noon to noon for dr. do not use GPS for noon DR. show the time of apparent noon. pre calculate sextant angle for apparent noon from dr lat latitude. show true latitude
then run to noon.

for a first timer if you are in the right ocean your about par for the course.
If you have done it half a dozen times you can expect to be still out by double didgets. if you have practiced before you went have a good sextant( not a davis) and it was a nice clear day on a steady boat you are within single didgets you should pass. you didnt fake it.

 

[G12]

Well said

Those who rant that astro nav is dated and no longer relevant only demonstrate ther own lack of experience and understanding of safe navigation. There is currently no back up to GPS when mid ocean other than a sextant and a little knowledge. Having no means of calculating position other than DR when mid ocean is not an acceptable or safe practice.

I agree with what you have said about astro but there IS an alternative to GPS. It's called GLONASS. I have previously worked for a company specialising in marine positioning for the likes of DP vessels, oil rigs, semisubs etc and we used GLONASS as well as GPS regularly. Our systems could typically produce a position accurate to 10cm.
You can get GLONASS on a little handheld receiver these days and I'm pretty sure once they get a few more satellites up you'll also be able to use the Galileo system too.
Even the iPhone 4s supports GLONASS.

 

[Doug_Stormforce]

I agree with what you have said about astro but there IS an alternative to GPS. It's called GLONASS. I have previously worked for a company specialising in marine positioning for the likes of DP vessels, oil rigs, semisubs etc and we used GLONASS as well as GPS regularly. Our systems could typically produce a position accurate to 10cm.
You can get GLONASS on a little handheld receiver these days and I'm pretty sure once they get a few more satellites up you'll also be able to use the Galileo system too.
Even the iPhone 4s supports GLONASS.

You are quite right, I should have said there is currently no back up to satellite navigation, other than the sextant.

 

[capnsensible]

I have absouloutly no idea who conducts rya exams.

If an examiner does not accept the use of a GPS position as a dr for your sight he or she is out to lunch. your DR could be a position selected by a pin stck in chart. The points they will be looking for are. did you name your intercept correctly.correct azimuth. and apply your corections in the right direction.

More can be deduced about your knowladge by watching you pick up the sextant and check the errors. use your left hand.

turning up with star sights having used a davis done in mid ocean from a small you are a bull****er.

Show up with a regular noon position taken using a GPS dr. Run to noon to noon for dr. do not use GPS for noon DR. show the time of apparent noon. pre calculate sextant angle for apparent noon from dr lat latitude. show true latitude
then run to noon.

for a first timer if you are in the right ocean your about par for the course.
If you have done it half a dozen times you can expect to be still out by double didgets. if you have practiced before you went have a good sextant( not a davis) and it was a nice clear day on a steady boat you are within single didgets you should pass. you didnt fake it.

Couple of points.

The RYA use experts who know what they are talking about.

Can you explain how, prior to gps, navigators were succesful despite sticking a pin in a chart?

A metal sextant is better, but it is perfectly possible to get a star fix mid ocean with a Davis. I can do this and so can my wife. I have no reason to exagerrate

Its all about practice.

 

[oldbilbo]

More can be deduced about your knowladge by watching you pick up the sextant and check the errors. use your left hand.....

Rather more can be deduced by watching you put your sextant back down again.....

 

[Uricanejack]

I thought at least one person would bite on my comment about a Davis. my point was a novice is unlikly to get a nice neet little cocked hat first time out

With practice no doubt you get satisfactory results.

I do not know the level of expertise required to be a RYA examiner. knowing what they are talking about would appear to be a sensible requirment. I did not intend to sugest they don't. I mearly expressed an opinion an examiner would not be concerened if a candidate started with a GPS position. it is the knowladge of the process after this which is required. perhaps an examiner will tell me I am wrong. If so I would be interested in why.

Prior to GPS. I went so fast for so long drew a line mesured the distance and made an X. The acuracy of the DR is not important. A pin stuck in the chart in the aproximate area and use nearest whole numbers will work just fine.

 

[Uricanejack]

Can you explain how, prior to gps, navigators were successful despite sticking a pin in a chart?


Well I will try.

When you take a sight. You are essentially measuring the distance from the objects geographical position.
If you had a really big compass (the drawing kind) you could stick it in the geographical position of the object. And draw a circle you would be some where on this circle of position. Two circles two crosses. One is where you is one is on other side of planet.

Naturally this is no very practical.

Instead we do a calculation using a dr or an assumed position and compare this distance to the measured distance. This will give us a distance to or from our dr to our observed or measured line of position. The direction of the line of position is the azimuth of the object which we also calculate. In theory all you need is the azimuth and distance for a position. This is not practical in most circumstances due to the great distance of the objects geographical position.

In effect if we were on the same vessel taking our sights at the same time. When you use your GPS and get an intercept or distance to your line of position of 2 miles. And I use my pin and stick it in the chart and get and intercept of 20 miles. We will end up with two different intercept terminal points through which our line of positions pass. We will both be on the same line of position.

If we use the same information, course and speed to run our ITP LOP to noon and observe the latitude which we can run to noon. We should theoretically be in the same place . Of course this is unlikely so we would just argue about where we are.