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Old 14-02-2013, 13:31   #691
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

Happy

My SMG was 4.1 knots
My CTS was 356

Some of this could be slight measurement error.

I used a slightly different methods for establishing the EPs and got roughly the same image. I used a single DR line with the cumulative effect of current.

You should be able to "eye ball" the last 15 minutes.

Should I post it?
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Old 14-02-2013, 15:10   #692
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

jackdale, sure, why not!


My own plot is a bit finicky trying to get within a degree and a tenth of a mile (which I could never ever actually steer anyways! )
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Old 14-02-2013, 15:11   #693
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Re: Deficiencies with RYA teaching:

Quote:
Originally Posted by Seaworthy Lass View Post
PRECISELY!
That is exactly what my method allows you to do. That is why you end up with the same result using my method as is calculated mathematically. If there is zero current at the end of the journey you simply connect the tip of the last 'boat displacement due to current' vector to B when you use the SWL method.

A big flaw with the RYA method is that they don't allow you to do this:



And again:



RYA instructors even amazingly say that "you can't have a constant heading if you have a period of slack at the end":



Then there were all the comments from this RYA instructor about how mathematically precise the RYA method is and how you arrived at B (not D) without changing heading of you followed the determined CTS:



Not only are you never at D according to how some instructors teach the method, but it is claimed the method will get you directly to the destination itself without changing heading:



It was again repeated that you never arrive at D using the RYA method, you "hit the rhumb at the destination directly" (D was several miles before B in this example):



The bottom line is that the RYA method is NOT a mathematically precise way of getting to the destination (B), yet it is taught that this is the case.

It is stressed that you do not arrive at D, but at B. This is plain incorrect.

I have said several times in previous threads that the RYA method is a good "rough and ready" method to get you close to the destination in most cases. The RYA does, however, not teach this. It attributes accuracies to this method that it simply does not possess.

Apart from presenting what I believe to be a better method for determining CTS, I have wanted to highlight that the RYA is not teaching students about the limitations of the actual RYA method itself (only of the data used for calculations).

Computing a CTS with variable cross current is very poorly taught by the RYA, yet all the instructors participating on this thread can say is that I am selecting unrealistic data for my computations .

The accuracy of the RYA method is not the only problem. How it is presented to students is the greater issue I would like to draw attention to!

WHat A rant SWL, trawling back and taking much out of context.

Quote:
That is exactly what my method allows you to do. That is why you end up with the same result using my method as is calculated mathematically. If there is zero current at the end of the journey you simply connect the tip of the last 'boat displacement due to current' vector to B when you use the SWL method.

A big flaw with the RYA method is that they don't allow you to do this:
Its not relevant in real life only in the gedankens you postulate. so what

Quote:
RYA instructors even amazingly say that "you can't have a constant heading if you have a period of slack at the end":
The context of this was I was thinking of one hour vectors. The RYA method does not specifically take into account the first 30 minutes of the last hour if vector sum places you in front of the destination. It does if its in behind as you deflate the triangle ( in that it ignores the last 30 minutes ).

Quote:
It was again repeated that you never arrive at D using the RYA method, you "hit the rhumb at the destination directly" (D was several miles before B in this example):



The bottom line is that the RYA method is NOT a mathematically precise way of getting to the destination (B), yet it is taught that this is the case.

It is stressed that you do not arrive at D, but at B. This is plain incorrect.

I have said several times in previous threads that the RYA method is a good "rough and ready" method to get you close to the destination in most cases. The RYA does, however, not teach this. It attributes accuracies to this method that it simply does not possess.
Is IS a mathematical correct way to get to the destination.( within the assumptions that the RYA apply to the tide data) If D is in front you stay on the CTS and the average of the tides bring you to B. If D is behind , you stay on the CTS and you arrive at B ahead of the tidal hour plot

This is based on the assumptions of the underlying tide data. PLease stop the persistent and misplaced crisitism of a method where you chooses to ignore the real life issue of accuracy.

Quote:
Apart from presenting what I believe to be a better method for determining CTS, I have wanted to highlight that the RYA is not teaching students about the limitations of the actual RYA method itself (only of the data used for calculations).
what do you know about the RYA classes, have you done them. Please stop this incessant rant , It ill becomes you .

Yours is not a better method, that can only be determined when it is compared against real life. Right now its a theoretical model with no proven correlation with real life.

Quote:
I have said several times in previous threads that the RYA method is a good "rough and ready" method to get you close to the destination in most cases. The RYA does, however, not teach this. It attributes accuracies to this method that it simply does not possess.
You have no demonstrated real life experience of this method, whereas the RYA has many years of such feedback.

I have no problem with somebody dreaming up , increasingly theoretically precise methods of multi hour CTS, I have HUGE problems when they compare their theories to one taught regularly and with the benefit of many years of feedback. Then I have HUGE problems when YOU start a continuous campaign of denigrating other methods other then your own , while failing to acknowledge that yours is based on a particular assumptions of that tide data. and I might add over 300 posts personally attacking me.

Assumptions that you have not sought to examine in reality , I might add.

Then you persist in the nonsense of what the RYA teaches and doesnt teach, yet to my knowledge you have admitted youve never been on an RYA course.

IN my case I make it very clear the limitations and my distrust in applying single CTS is complex multi hour situations. I outline how real life errors and effect s make it virtually impossible to apply. I point out that in situations where the tide approaches a significant percentage of boats speed, that there are large risks that one can get caught out. I point out that unplotted ground tracks that result in excursions from the rhumb line can be unsafe.

I have said repeatidly that your mathematical methods, assuming you treat the data precisely as you do , result in a more "precise" answer. I have repeatidly counterbalanced that ( as has Jackdale) that in real life Accuracy is a different thing and your methods have NO proof of any greater accuracy. And even then your method would have to be reasonable better , rather then just better to justify the extra work and potential confusion

Why you are on a mad crusade about this I cant fathom. contributing a "different " theory is all very well, lambasting all around you is another, yet you have never engaged in a debate about the assumptions in your "theory" , not rengaged in a real debate about the usefulness of these ( all of them ) methods in real life. ( you actually stated yourself youd stay near the rhumb line)

Dave
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Old 14-02-2013, 15:23   #694
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

Quote:
Originally Posted by HappySeagull View Post
jackdale, sure, why not!


My own plot is a bit finicky trying to get within a degree and a tenth of a mile (which I could never ever actually steer anyways! )
I need to add some labels.

But right now I need to pick my wife up from a first aid course and take her out for dinner. Apparently today is something special.
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Old 14-02-2013, 16:09   #695
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

jackdale, labels are hard to not overwrite each other! If you need to, I offer as a suggest- just making temporary mark (no icon- O has this option) and writing info into the name. I should have done that!

However your plot sounds like it'll be right in the clump for sure. Try to speculate what happens after 1045, when the data runs out- a bit odd I'd say, that it wasn't included in the book....

I expect SWL's plot will be closer to the mark as the SWL method IS about averaging the last bit.

on the other hand, if the RYA method does (secretly) average current, my red dotted lines would be extreme and the RYA would pass closer to Destination (redflag)... say, a half mile instead of 3/4 mile

I can't see anything wrong with trying to get more accuracy, simply. But it's not my feathers being ruffled either.
It would be interesting (but time consuming) to see how an autopilot would score....at say 15 minute intervals. I think it would be a bit behind for sure, but being so near the rhumb line...one must not forget that when "the books were writ", for yachts, autopilots were not exactly mainstream and without some consideration of drift, hapless folk would be out of the race entirely.
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Old 14-02-2013, 16:26   #696
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pirate Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

Tide's a real buga round here...
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Old 14-02-2013, 17:21   #697
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

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Tide's a real buga round here...
So's that popcorn. Not fresh. I wouldn't eat it if I were you.
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Old 14-02-2013, 17:50   #698
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Quote:
Originally Posted by Seaworthy Lass

Yes, in the rare example that the journey takes precisely a whole number of hours, and D therefore coincides with B, a line can be connected between C and B using the RYA method. Otherwise it is taught that C cannot be connected with B, even if there no current at the end of a journey.
Sheesh again this is not a correct application of the theory. You plot the journey as a sum of hourly tide vectors. Then you arc off the same equivalent boat time vector. Of the intersection, is more then 30 minutes you should allow a further tide hour. ( 0 is still a vector )

Only of such a multiple of hours of boat speed and tide should happen to coincide with the destination., would the Arc cut through the destination.

In essence these are hourly plots hence everything must be in units of hours. To then compute the time you proportion the journey at the average rate of advance. The RYA method does not change the CTS vector within a 30 gap before arrival time. It merely assumes that the tidal change s gradual and therefore the resulting error is acceptable and less that that experienced in real life.

As I said in practice , in real life , where currents are reasonably less that boat speeds the resulting answer has been seen to be adaquate.

That's all there is, the whole is single CTS in multi hour complex situations has too many issues going for it to be concerned over increasing mathematical precision, which arguably does not result in any increase in accuracy in real life.

Dave
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Old 14-02-2013, 17:55   #699
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Quote:
Originally Posted by HappySeagull
at 1045, (2 1/2 hours from start) most "methods" are going to be ~0 .85 miles from destination...? From this example, where current is increasing, it's the last mile - the last 15 minutes -that is , aah,"important".

It's not clear to me in this example and other "reasonable" ones why the example boat won't just tweak her way home when she spys a mark.
Of course that's what happens. In real life.

But again your missing the point. The tide is not constant over the hour , hence both methods are fallible. Until you compare each method to a source of greater accuracy and small time quantums you can't draw any conclusions as to their " accuracy ". Even then such accuracy is more then likely swapped by real life sailing errors, resulting in an meaningless unachievable improvement in theory only.

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Old 14-02-2013, 18:18   #700
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Re: Deficiencies with RYA teaching:

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Is IS a mathematical correct way to get to the destination.( within the assumptions that the RYA apply to the tide data) If D is in front you stay on the CTS and the average of the tides bring you to B. If D is behind , you stay on the CTS and you arrive at B ahead of the tidal hour plot
Dave
Nope.

In the last example where you say you would have computed a CTS of 157 degrees, could you please settle this argument and show us how this would get you to B in 2.4 hours by providing us with a diagram of the ground track?

After a wonderful evening I am feeling far too mellow to address anything else in your post .

Happy Valentine's Day everyone xxxxxx.
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Old 14-02-2013, 18:25   #701
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

Real life ! 47 pages and counting...? Do we have a "real life"?

add: SWL, I am trying yer method - have to fudge the last hour of current as "2 miles" as I did in the sketch. ie: 1045-1145 is the same as 0945-1045 because the example from the book didn't give me more.
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Old 14-02-2013, 18:36   #702
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Originally Posted by Seaworthy Lass

Nope.

In the last example where you say you would have computed a CTS of 157 degrees, could you please settle this argument and show us how this would get you to B in 2.4 hours by providing us with a diagram of the ground track?

After a wonderful evening I am feeling far too mellow to address anything else in your post .

Happy Valentine's Day everyone xxxxxx.
Again seaworthy you can only compare accuracy with real life and not model to model. The RYA takes slightly different assumptions on the underlying data. You make different ones. For you with those assumptions your model is more precise. It's doesnt of course mean its more accurate

There's no point doing a breakdown n each method by simply using the same theoretical data from whence the answer was computed. The only way you can determine which method is more accurate rather then which method is more precise is by doIng a fairly rigorous real life analysis with far more tidal data then presented.

This is to work out the errors that exist by using average tides with rigid time boundaries in your method.

Anyway are you seriously arguing that a difference between 152 and 157 has any real application in a long multi hour journey. Nobody navigates to these types of numbers.

It's all angles on a pinhead.

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Old 14-02-2013, 19:20   #703
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

Click image for larger version

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ID:	54796Click image for larger version

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ID:	54797 ok, I got CTS=002 per SWL method, Missed the flag, but I suppose I didn't do it right...

(you have a point there,goBoat'. This is an awful lot like golf )
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Old 14-02-2013, 19:29   #704
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ok, I got CTS=002 per SWL method, Missed the flag, but I suppose I didn't do it right...

(you have a point there,goBoat'. This is an awful lot like golf )
Yes , a good walk ruined l or in this case a sail. !!! Anyone who suggests , in either of your drawings, you have missed the destination is of course talking nonsense.
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Old 14-02-2013, 20:17   #705
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

My drawing



I did not change symbols.

I used the convention for establishing a EP by using a DR and accounting current.

Dave - I would appreciate any comments.

Jack
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