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Old 19-02-2013, 17:43   #781
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

In one of the earlier SWL scenarios the best plan was to wait an hour.
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Old 19-02-2013, 19:14   #782
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

Quote:
Originally Posted by jackdale View Post
In one of the earlier SWL scenarios the best plan was to wait an hour.
Yes, and I haven't forgotten that episode-but reason does not apply here!!
being the swl challenge to lodesman's alternate method.Imight have the answer ormight not butit woked this time.
Further, I want also to have a "Hapless" solutionto this problem as well,toget a different CTS, buttimedoesnotpermit nor will this laptop.
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Old 19-02-2013, 19:44   #783
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

Quote:
Originally Posted by Seaworthy Lass View Post
Wine and a comfy settee and a good movie have slowed me down tonight, but here is an example for you to try:

B is 3nm from A, bearing 30 degrees true
Boat speed is 2 knots, motoring in calm conditions
Current:
Average for first hour: 3.0 knots 77T
Average for second hour: 1.4 knots 77T

What is the CTS and time taken?
Quote:
Originally Posted by HappySeagull View Post
even given overpowering current,
lodesman method does work if you assume closest approach which is 90 degrees per A-.B line to 1 hour current....
What Happy said. I scribbled my work on foolscap, so no guarantee on accuracy - I got 312º for 1h23m.

But work backwards, sit around for 55 minutes, then steer 000º for 1h5m - Nigel nailed it.
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Old 19-02-2013, 20:47   #784
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

Quote:
Originally Posted by nigel1 View Post
Think I'd spend another hour reading my book and then set off steering roughly north, and save a few liters of diesel, save enough diesel and I could buy an engine which would make better than 2 kts.
Quote:
Originally Posted by jackdale View Post
OK
Nigel is correct - wait one hour. Steer 004 ETA 1 hour SMG 3.0 knots
Or leave immediately steer 317 ETA 2 hours SMG 1.5 knots
Do you want the plot?
Quote:
Originally Posted by Lodesman View Post
But work backwards, sit around for 55 minutes, then steer 000º for 1h5m - Nigel nailed it.
Lads, waiting is NOT an option.
Who said the departure point was close to shore?
And it is far too deep to anchor and wait, regardless of whether you have a Sarca, Bruce, CQR or whatever!

This is the very last portion if a long journey. Yes, you have foolishly just about run out of fuel (small vessel) and really want to conserve the fuel in case it is needed at the end.

Or maybe this is one of the legs racing. The wind unexpectedly died off at the beginning if the previous leg. Two knots is the average speed you think you will do.

Hanging around is NOT an option. These CTS techniques are not simply for the start of a journey! These two scenarios are not far fetched at all. You need a technique of determining CTS that will handle any data thrown at it.

I will wait until replies are in before posting the answer .
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Old 19-02-2013, 20:53   #785
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

Quote:
Originally Posted by HappySeagull View Post
sure- wait an hour and catch no fish!

given A-B 3 miles bears 30T
boatspeed 2 knots
drift hour 1 =3 miles@77T, hour 2= 1.4 miles@77T

Boat CTS= 316-317.
Boat sails about 2.5 miles 1 hour 15 minutes

Attachment 55249
even given overpowering current,
lodesman method does work if you assume closest approach which is 90 degrees
D is on the rhumb line.
I would respectfully like to point out to noble gulls that you cannot arc off D1 after an hour as it does not reach the rhumb line. I humbly request a diagram of how examining D1B/D1B+BD2 is going to work in this example.

If D is not on the rhumb line and you are arcing off towards B then that is the SWL method.
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Old 19-02-2013, 23:14   #786
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

yawk! "Noble seagull" - did I get some hard pecks in the raft tonight! see, we leave that word for the nasty,stupid, murdering , noble, vicious sneaky, awkward, gluttonous, cruel, avarcious cousins of vultures. Not that we blame Vultures. We know family can be a cross to bear ....

No, it's not the SWL method.
here's one with the marks in place. line D1 is two miles long and does not touch the rhumb.at D1. the d1 line shows the boat's closest approach possible to the rhumb given the current for the period.
the rest is merely proportion as before.

Click image for larger version

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arcing ...I can't actually do that with OpenCPN's route pencil
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Old 19-02-2013, 23:50   #787
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

Quote:
Originally Posted by HappySeagull View Post
yawk! "Noble seagull" - did I get some hard pecks in the raft tonight! see, we leave that word for the nasty,stupid, murdering , noble, vicious sneaky, awkward, gluttonous, cruel, avarcious cousins of vultures. Not that we blame Vultures. We know family can be a cross to bear ....

No, it's not the SWL method.
here's one with the marks in place. line D1 is two miles long and does not touch the rhumb.at D1. the d1 line shows the boat's closest approach possible to the rhumb given the current for the period.
the rest is merely proportion as before.

Attachment 55267

arcing ...I can't actually do that with OpenCPN's route pencil
"Noble" was not a peck LOL, but a mark of respect. I think one Seagull has had too many pecks lately and doesn't see the compliments.

The definition of D is where the the boat displacement due to speed for a whole number of hours intersects with the rhumb line. It is not where it gets close to the rhumb line. It is where it INTERSECTS.

It is a totally different method if you start saying D (and you need to rename it then, for it is not D any longer) does not have to intersect the rhumb line.

It is simply not possible with this example to get a reasonable result with either the RYA method or a modification of this, ie looking at where D intersects the rhumb line before then after B and looking at the proportion of the lengths of undershoot vs overshoot plus overshoot (the first method I came up with in AndrewTroup's thread a month ago, and which you and Lodesman are now proposing).

The reason for it is the fixation with the rhumb line.

Why not just aim the boat displacement vectors towards the destination instead? (= SWL method). It is no harder and certainly it is more accurate and it can handle any data.

Why this fear and resistance of aiming at where you want to go?
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Old 20-02-2013, 00:55   #788
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

The definition of D is where the the boat displacement due to speed for a whole number of hours intersects with the rhumb line. It is not where it gets close to the rhumb line. It is where it INTERSECTS.

.. but that's not a rule in this method.

It is a totally different method if you start saying D (and you need to rename it then, for it is not D any longer) does not have to intersect the rhumb line.

This is the Lodesman- RYA Beta 2 Method, I suppose....
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Old 20-02-2013, 01:06   #789
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

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Originally Posted by HappySeagull View Post
The definition of D is where the the boat displacement due to speed for a whole number of hours intersects with the rhumb line. It is not where it gets close to the rhumb line. It is where it INTERSECTS.

.. but that's not a rule in this method.

It is a totally different method if you start saying D (and you need to rename it then, for it is not D any longer) does not have to intersect the rhumb line.

This is the Lodesman- RYA Beta 2 Method, I suppose....
OK, fair enough.

But I would love to know how this method is even one tiny scrap easier than the SWL method? (Proportions are needed to be calculated and applied in EXACTLY the same manner). And what advantages does it have over the SWL method?

I agree though, it is superior to the RYA method .

I wish you and Lodesman much luck in having your method considered. I would be thrilled to have any improvements made to the RYA method regardless of who is proposing them, even if the accuracy is not quite as good as my method.

I have come up against a brick wall (make that metre thick steel wall) of resistance when pointing out the problems with the RYA CTS technique. The RYA method has apparently been taught for decades and is considered "mathematically precise" and infallible and is definitely not open to improvement .
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Old 20-02-2013, 07:42   #790
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

Quote:
Originally Posted by Seaworthy Lass View Post
"

Why not just aim the boat displacement vectors towards the destination instead? (= SWL method). It is no harder and certainly it is more accurate and it can handle any data.

Why this fear and resistance of aiming at where you want to go?
I'll give you that your method is relatively easy, but it is certainly not more accurate. You're comparing two different triangles to estimate the partial hour.
As I said previously, your method has merit where someone regularly needs to calculate a multi-tidal single CTS, but it has little utility beyond that. The basic tidal triangle can be used for all your navigation needs.
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Old 20-02-2013, 09:44   #791
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

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Originally Posted by Seaworthy Lass View Post
Lads, waiting is NOT an option.
Who said the departure point was close to shore?
And it is far too deep to anchor and wait, regardless of whether you have a Sarca, Bruce, CQR or whatever!

This is the very last portion if a long journey. Yes, you have foolishly just about run out of fuel (small vessel) and really want to conserve the fuel in case it is needed at the end.

Or maybe this is one of the legs racing. The wind unexpectedly died off at the beginning if the previous leg. Two knots is the average speed you think you will do.

Hanging around is NOT an option. These CTS techniques are not simply for the start of a journey! These two scenarios are not far fetched at all. You need a technique of determining CTS that will handle any data thrown at it.

I will wait until replies are in before posting the answer .
Waiting is always an option.

This is clearly not a race scenario.
Quote:
Boat speed is 2 knots, motoring in calm conditions
I am a fanatic about fuel consumption. If you take a look at my videos of the medevac you will see extra fuel tanks. For a 2500 mile trip I has enough fuel for 1300 miles at 1700 rpm (about 5 knots). Some of us are not that foolish. The "rule" I teach is 1/3 out, 1/3 home, 1/3 in reserve.

The example is too extreme and unrealistic, as are others that you have presented. Please use a real voyage with real courses and real current tables. The examples that I have presented, with the exception of the channel crossing, have come from real charts and current tables. You must have those on your boat. Or, since you obviously have internet, download a copy of OpenCpn and some NOAA charts. OpenCPN has current data embedded.
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Old 20-02-2013, 11:43   #792
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

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Originally Posted by Seaworthy Lass View Post
OK, fair enough.

But I would love to know how this method is even one tiny scrap easier than the SWL method? (Proportions are needed to be calculated and applied in EXACTLY the same manner). And what advantages does it have over the SWL method?

I agree though, it is superior to the RYA method .

I wish you and Lodesman much luck in having your method considered. I would be thrilled to have any improvements made to the RYA method regardless of who is proposing them, even if the accuracy is not quite as good as my method.

I have come up against a brick wall (make that metre thick steel wall) of resistance when pointing out the problems with the RYA CTS technique. The RYA method has apparently been taught for decades and is considered "mathematically precise" and infallible and is definitely not open to improvement .
Not my method. It's just another method. I'd have to play with both awhile to see which I like as more elegant.




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Old 20-02-2013, 11:55   #793
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

here's one I made up this morning. There are more, I guess, but it takes awhile to figure out how to draw them. This solves the last problem, in case it's not plain. A bit of a toughie to line up in the O routing sketcher but on paper, I think should be practical.

Not hanging my gonads on it so fire away.

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Old 20-02-2013, 13:05   #794
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

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Not my method. It's just another method. I'd have to play with both awhile to see which I like as more elegant.


Hi Happy
You have missed out the first hour of boat displacement due to current in the first lot of computations . Given this, how is it you came up with the same result for each method?
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Old 20-02-2013, 13:26   #795
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Re: Inaccurate RYA Teaching : CTS - Quest For a New Method

no, it's there, but the mark isn't showing .Check the proportions of current vectors- both are equal.
scales are not same though.these appear as one picture but there are two. linked from up-thread.
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