Yottigation

[Koeketiene]

I agree - tidal curve is a factor, but as an estimation the rule of 12ths is more than good enough if you add in a safety margin.

Even tidal calculations to within 10cm worked out the RYA way have to allow for a safety margin - after all, the seabed is not exactly flat, is it?

 

[Birdseye]

[ QUOTE ]
When doing the YM Theory at night school, the lecturer explained that we needed to work out tidal heights and tide times to the nearest 10 cm and 1 minute.

Then he showed us a slide taken from a web site (the URL of which I knew once but have now forgotten!) and proudly told us that this web site demonstrated that at the local recording station (Felixstowe), on not one day in the last 2 weeks had either the tide height or tide time been in accordance with the prediction.

I put my hand up and said "What is the point of working it out to 10 cm and 1 minute then" and he said "because that's what the RYA say for the course".

Am I missing something obvious? Can anyone else understand this?!

[/ QUOTE ]

Absolute tosh. It isnt possible to work out tide times to 1 minute using the tidal curves in the PNT though it is possible to work out theoretical heights to the nearest 10cm. And to the best of my knowledge there is no RYA specification that you should be able to work to these limits. Apart from the colregs test where there is rightly an 80% pass mark, the main requirement for the other papers (per the Instructors Handbook) is that " the student must have understood the concepts taught and has sufficient knowledge to convert the theory into practise" . To my mind this would mean an understanding that tide predictions are not accurate to 1 minute and 10 cm , and that to plan on this basis is foolhardy.

In a way, it sounds as if your instructor is making this point to you with the comparison to the Felixstowe data.

As a matter of interest, what does your instructor say about the accuracy of plotting? Does he give you a real understanding of the likely accuracy and sources of inaccuracies, or does he insist you plot on the chart to within 10 metres?

/forums/images/graemlins/laugh.gif

 

[Pye_End]

Don't think the examiner is expecting real life to be this accurate, just that you can do a tidal calculation.

If you are marking answers only it is either right or wrong, hence the need for an accurate answer.


The real life data is interesting particularly in extreme weather. Quite often the hills and the valleys are fairly different, but the curve in between seems to follow a much more accurate path to the predicions. Strange, as you would have thought that if you have a high pressure or a low pressure then the whole lot would be above or below.

 

[Searush]

As two people have already said, it's all about maring papers in an exam situation.

Real life is the rule of 12ths plus a bit. And a bit more if there are waves or the bottom is hard or rocky, I often use a bit less if trying to get on/off my mooring which is soft mud & well capable of allowing bilge keeler tram lines!

Risk assessment is all about 2 things;
1 Risk of it happening, and
2 Consequences of failure.

If the consequences are serious, you don't risk it unless the chances of it happening are very low! etc