YM Ocean

[steveej]

Hi everyone,

I'm about to depart for my ocean qualifying passage in the next few days. I have gone through all the online theory twice but have not sat the exam as I have run out of time but will do so when I get back.

Some questions for people who have done this.......

RYA requirements state the minimum for the oral is Sun Run Sun meridian sight plus a compass check.

Q1 how do people practically carry out the compass check given you need to build a pelorus and you dont necessarily know the boat or size of shiops compasss until you turn up?

Q2 does this just mean noon-noon runs and do you need to factor in current to your dead reckoning position? If so, do you need JImmy cornells routing charts to get this information (I have them but would rather not carry them on the plane)

Q3 Can I just ignore all the star stuff including Polaris?

Worldwide met, maintenance, seaworthiness and provisioning I don't have a problem with.

Any other tips?

Thanks

 

[Deleted member 36384]

Q1 I have done this twice, once with a compass that had a shadow line from a pin in the compass card and on another I used a screw driver to sight through the centre of the card to the sun. When you calculate the azimuth to sun you then note the yachts steering compass bearing to the sun and do the arithmetic following the usual conventions applying variation to get the magnetic bearing. The difference between the calculated magnetic and the yachts steering compass magnetic is the deviation. You then repeat at sun set, for example, or the noon sight, or the next sun run sun sight.

Q2 Factor in leeway and current. There are other sources of current.

Q3 You can be questioned on any part of the syllabus IIRC but don't have to show position by stars. Stars are easy once you have practised but I could not do it now. Gives you a neat fix straightaway.

That's how I remember it from back in the '89, happy for anyone to correct who is is more current than me.

 

[prv]

I used a screw driver to sight through the centre of the card

Brass one, I hope

(Or not a magnetised one at least )

Pete

 

[Skylark]

It’s ok to keep your DR log simple. Distance and bearing since last fix, ensuring that any tacks or other course changes are noted and plotted. Adding an allowance for leeway and tide isn’t generally necessary, unless for example you’ve been hove-to in a storm for a few days and not seen the sun. The DR position is a key piece of information required for the sight reduction process.

On a days run, it’s “usual” to take a series of 3 sights. Forenoon, MP and Afternoon. Using transferred position lines of the earlier sight will give the running fix, aka sun-run-sun.

It’s not hard to improvise a Pelorus, use something plastic. Knowing Zn from your sight, it’s straightforward to use this, ships heading and local variation to create one line of a Deviation Card.

The navigation narrative for the qualifying passage should include a sun-run-sun and compass check as a minimum.

When taking the oral, if you do not have the Shorebased YMOcean course completion certificate you’ll have to sit a separate theory exam. I don’t know for sure but I suspect that this is the same paper as used for the Shorebased course. That being the case, there could well be questions on sight reduction of the moon, planets, stars or Polaris, plus on any other parts of the syllabus.

My oral exam was a couple of hours chat, drinking tea with a very experienced sailor, generally talking about ocean passage making. Absolutely anything related to this was fair game for questioning. Anything from TRS to crew welfare, victualling, repairs and maintenance, energy, water.......the list is endless.

 

[zoidberg]

I don't believe it is practical to use a bulkhead-mounted compass to establish the compass bearing of the sun by 'shadow pin'. Some years ago, when being 'zamined by a notoriously-crusty RYA Ocean Examiner who was rightly grumpy due to my arriving over an hour late ( trapped on motorway - no mobo signal ), he asked me to explain how I'd managed the daily compass checks for deviation I'd included in my journal. I pulled out the pelorus I'd made up from a reclaimed RN bridge-wing dumb compass complete with sighting prism. He grinned, then dug out his own - made from perspex - he'd constructed years previously, and we compared. There were no more 'challenging' questions......

Based on that, I can but recommend that the OP make up his own pelorus.

What's also quite desirable is a 'Table of Sun's Amplitudes'..... See Reeds Astro Navigation Tables - and my endorsement on the back cover.

 

[steveej]

ok, so for the pelorus, I have made up a CD with a paper print out I got off the internet showing with 360 degree graduations. I have yet to work out what I am going to use for the pin.

Some of the books I have been reading refer to 'amplitude tables' which give the bearing of the sun at sunrise and sunset depending on latitude - I cannot seem to find this in the 2018 Nautical almanac or my sight reduction Ap3270. So if I haven't got that I take it I need to work out UT for the time of local sunrise from the day tables with a correction for arc, then work out my LHA, chosen position etc and take it to the sight reduction tables to get the bearing to the sun?

Assuming the boat is heading directly north, I can place my CD in its case lined up fore and aft with the ship, note the shadow from the pin and take the reciprocal bearing, compare this with the bearing from the tables and the difference will be Variation + deviation. And if you know the variation you can work out your deviation.

What have I missed?

I think the process should be like this but please correct me if I am wrong.

Work

 

[steveej]

It’s ok to keep your DR log simple. Distance and bearing since last fix, ensuring that any tacks or other course changes are noted and plotted. Adding an allowance for leeway and tide isn’t generally necessary, unless for example you’ve been hove-to in a storm for a few days and not seen the sun. The DR position is a key piece of information required for the sight reduction process.

On a days run, it’s “usual” to take a series of 3 sights. Forenoon, MP and Afternoon. Using transferred position lines of the earlier sight will give the running fix, aka sun-run-sun.

It’s not hard to improvise a Pelorus, use something plastic. Knowing Zn from your sight, it’s straightforward to use this, ships heading and local variation to create one line of a Deviation Card.

The navigation narrative for the qualifying passage should include a sun-run-sun and compass check as a minimum.

When taking the oral, if you do not have the Shorebased YMOcean course completion certificate you’ll have to sit a separate theory exam. I don’t know for sure but I suspect that this is the same paper as used for the Shorebased course. That being the case, there could well be questions on sight reduction of the moon, planets, stars or Polaris, plus on any other parts of the syllabus.

My oral exam was a couple of hours chat, drinking tea with a very experienced sailor, generally talking about ocean passage making. Absolutely anything related to this was fair game for questioning. Anything from TRS to crew welfare, victualling, repairs and maintenance, energy, water.......the list is endless.

Thanks that's helpful.

So you can do the compass check at the same time as taking the Fornoon sight, using the Zn from the tables and comparing your pelorus shadow with adjustments for the ships heading?

 

[alant]

Hi everyone,

I'm about to depart for my ocean qualifying passage in the next few days. I have gone through all the online theory twice but have not sat the exam as I have run out of time but will do so when I get back.

Some questions for people who have done this.......

RYA requirements state the minimum for the oral is Sun Run Sun meridian sight plus a compass check.

Q1 how do people practically carry out the compass check given you need to build a pelorus and you dont necessarily know the boat or size of shiops compasss until you turn up?

Q2 does this just mean noon-noon runs and do you need to factor in current to your dead reckoning position? If so, do you need JImmy cornells routing charts to get this information (I have them but would rather not carry them on the plane)

Q3 Can I just ignore all the star stuff including Polaris?

Worldwide met, maintenance, seaworthiness and provisioning I don't have a problem with.

Any other tips?

Thanks

Compass check?
Just point the boat at the Sun & check your binnacle, no need for a 'Blue Peter' pelorus.

 

[Deleted member 36384]

Compass check?
Just point the boat at the Sun & check your binnacle, no need for a 'Blue Peter' pelorus.

No, that is only valid for that heading (towards the sun) on the ships compass as it is a single bearing measurement, the course you are actually steering may have a different deviation. The whole point of the exercise is to check for the course you are heading to verify the deviation. Neither can you sail around in circles taking the bearing because the sun moves, unlike the practise when using a far away land mark onshore.

 

[Skylark]

Thanks that's helpful.

So you can do the compass check at the same time as taking the Fornoon sight, using the Zn from the tables and comparing your pelorus shadow with adjustments for the ships heading?

Yes, use Zn from any sun sight. I’d also follow the recommendation by zoidberg and make a pelorus; I’m sure that professor Google will help.

Good luck, hope you enjoy the passage.

 

[alant]

No, that is only valid for that heading (towards the sun) on the ships compass as it is a single bearing measurement, the course you are actually steering may have a different deviation. The whole point of the exercise is to check for the course you are heading to verify the deviation. Neither can you sail around in circles taking the bearing because the sun moves, unlike the practise when using a far away land mark onshore.

The purpose is to obtain compass error, which is a combination of deviation & variation.
On a small yacht, unless on a perfectly flat sea the deviation error due to course/heading shouldn't be much different to your deviation card. Taking a back bearing won't be any more accurate using a home made pelorus. On a big ship, you can get accuracy but unlikely when being bounced around in a small plastic (or steel for some) yacht.

 

[Deleted member 36384]

The purpose is to obtain compass error, which is a combination of deviation & variation.
On a small yacht, unless on a perfectly flat sea the deviation error due to course/heading shouldn't be much different to your deviation card. Taking a back bearing won't be any more accurate using a home made pelorus. On a big ship, you can get accuracy but unlikely when being bounced around in a small plastic (or steel for some) yacht.

The purpose is to check for the course you are sailing, not another course. The reason for the check is to confirm that the deviation is in accordance with that which has been measured accurately and noted in the card. Even in coastal sailing, there is a historical precedence to check the accuracy of the compass from time to time, such as on transits. This is for a few reasons, it’s an independent check from the card, correcting magnets or the soft iron balls, could be displaced and make the previously measured deviation wrong, there is an imperative to find out sooner rather than later that the expected deviation is wrong, especially on long passages. You are not calculating deviation because it’s not known, it’s just a check that is convenient to do in a featureless ocean.

I do get what you mean, but by moving the boat, you may get a false positive, if the condition to cause the deviation to change is not stable e.g. magnets moving because of some mechanism failure. The accuracy is questionable anyway, on a yacht steering compass that is marked in 5 degree intervals and is probably swinging around another +/- 5 degrees as well. The practise is almost irrelevant anyway with modern plotter systems.

 

[zoidberg]

Some of the books I have been reading refer to 'amplitude tables' which give the bearing of the sun at sunrise and sunset depending on latitude - I cannot seem to find this in the 2018 Nautical almanac or my sight reduction Ap3270.

What have I missed?

I told you in #5.

This is also readily found in, for example, Reeds Nautical Almanac 2017 ( to hand ) p. 48. and many other similar publications..... Burton's, Norie's.....

 

[steveej]

Thanks Zoidberg.

I have the Reeds but have not been using it as very few of the table are used in the RYA theory course and many which are used are not included in the Reeds. I have been using the Nautical Almanac 2018 and AP3270 sight reduction tables from the Hydrographic Office.

 

[Skylark]

steveej,

You’re not talking the same “Reeds”.

zoidberg is referring to Reeds Nautical Almanac, as found on the vast majority of UK Cruising boats. Under section 3 Navigation, it shows how to check a compass for accuracy by using Tables 3(4) and 3(5), sun declination and true bearing of sun at sunrise and sunset.

You are referring to Reeds Astro Navigation Tables. These use the ABC method to reduce a sight. As you rightly say, the RYA course teaches the use of the Intercept Method, aka Marcq st Hilaire, using AP3270 Tables.

Hope this helps.

 

[steveej]

steveej,

You’re not talking the same “Reeds”.

zoidberg is referring to Reeds Nautical Almanac, as found on the vast majority of UK Cruising boats. Under section 3 Navigation, it shows how to check a compass for accuracy by using Tables 3(4) and 3(5), sun declination and true bearing of sun at sunrise and sunset.

You are referring to Reeds Astro Navigation Tables. These use the ABC method to reduce a sight. As you rightly say, the RYA course teaches the use of the Intercept Method, aka Marcq st Hilaire, using AP3270 Tables.

Hope this helps.

Thanks for the clarification, the reeds astro that I bought back in January is a complete waste of time then.

 

[Skylark]

Thanks for the clarification, the reeds astro that I bought back in January is a complete waste of time then.

That's one way of looking at it, I'm afraid.

The ABC method does have its fans, though. Perhaps offer it in the For Sale section......or there's always ebay

 

[zoidberg]

Thanks for the clarification, the reeds astro that I bought back in January is a complete waste of time then.

It most certainly is not 'a complete waste of time'. I'll have it from you if you continue to think that and, living just a few miles from the OP's lair, that would be easy enough to arrange.

David Jackson is quite right. I have referred to TWO Reeds publications - one so entirely ubiquitous that I had assumed the OP and everyone else on here would be fully familiar with it..... and the other, what Lt Cmdr Harry Baker calls 'Reeds Heavenly Bodies' before the snowflakes at Bloomsbury took over publishing it, now called 'Reeds Astro Navigation Tables'

FWIW, I was trained to use the Air Tables and Almanac - up in the air - long before the RYA weaned themselves off the Nautical Almanac, making the task of sight reduction just a little less cumbersome. Memory - and 'Bowditch' - tells me that there have been in excess of 50 different 'short methods' and 'look up tables' invented over the years - all intended to simplify the task and avoid the need for Sight Reduction By First Principles i.e spherical trigonometry sums.

The Reeds Astro Navigation Tables booklet, originated by the bright-as-a-button Harry Baker, was IMHO the simplest, easiest, most convenient and cheapest of these, and I chose to use it throughout my own 'qualifying passage' from Liverpool Bay, outside Ireland and down to La Corunna, entirely by traditional techniques.... including at least one Compass Check By Suns Amplitude each day the sun was visible. That last was the easiest of the tasks....

Both the Air Tables/Marc St Hilaire AND Harry Bakers' ABC method work well for yotties. One is a darn sight cheaper and more convenient to use on a small boat than the other......

It needs to be remembered that the holder of an RYA Ocean Certificate is but a couple of step away from adding a Commercial endorsement, and that could lead to other innocents trusting their lives, and perhaps those of their children, to the knowledge and judgement of the certificate holder.

 

[capnsensible]

You got amplitude tables, you got Norries and you can knock out a quick zn anytime you like. But it's as much use on anything less than a container ship as a chocolate fire guard and as accurate as a Donald Trump tweet.

Dunno why it's still in the syllabus.

From a contributed who tried it several times again last week in the middle of a calm Atlantic!

 

[capnsensible]

You got amplitude tables, you got Norries and you can knock out a quick zn anytime you like. But it's as much use on anything less than a container ship as a chocolate fire guard and as accurate as a Donald Trump tweet.

Dunno why it's still in the syllabus.

From a contributed who tried it several times again last week in the middle of a calm Atlantic!