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Old 03-02-2013, 15:32   #121
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Re: Single CTS or follow the Courseline?

Quote:
Originally Posted by goboatingnow View Post
I despair in some of the comments.

Constructing ground tracks in multi hour CTS is not something people are taught nor is it intuitive.

Whether one uses the RYA or the SWL method is irrelevant, you cannot monitor your progress unless you know where you are supposed to be. In a multi hour CTS that's not easy.
If it isn't taught it should be it only takes a few simple steps to draw the hourly tide vector, then the boat vector, then repeat for the duration of the passage. In Open CPN it can be done in about 20 seconds for each hour of passage.

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Originally Posted by goboatingnow View Post
Secondly you may even be on your computed ground track ,but early or late.
If you plot a ground track you will have a very good idea!

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Originally Posted by goboatingnow View Post
Hence you have to now evaluate what tides are valid. In some cases you could find significant course changes are required its not simple and bill raises a valid point that has not been addressed
If you are advocating following the rhumb line on your chart plotter, then look at the tide vector and compare to your planning data!

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Originally Posted by goboatingnow View Post
Mention has been made of criticising the criticism of the variables . It is entirely appropriate to do so. This are models and like all models you have to relate them to real life and in practice they do not work well.

Furthermore the RYA method does not leave you swinging in the wind for the last 30 minutes nor does it " get you close ". The method correctly applied gives you a theorctical. CTS to the estivation. The discussion is over the method used ( hence where the variables argument vibes in)
Yes both the RYA and CTL methods are planning tools to help you on your way. Comparing a planning tool to an autopilot holding a rhumbline track is comparing oranges to apples.
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Old 03-02-2013, 15:35   #122
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Re: Single CTS or follow the Courseline?

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Originally Posted by goboatingnow View Post
I have repeated questioned the real life valve of multi hour especially large multi hour CTS. That's been the key point of my posts in three threads for early two weeks. Using the method over 2-3 changes of tide is practical, more in my opinion is not

Working up the CTS vector is easy enough. Working up the ground tack isn't. Without the ground track you have no way of ascertaining where you should be.

What people fail to realise is that not that its difficult to determine your position, you can use EPs, sextants , GPS , voodoo whatever. Since you don't have an accurate ground track you can't easily determine if your following your precomputed plan.

So the only other way is to continually recompute the whole plan and determine a new CTS from where you are now. That's a lot of work in complex situations.

The advantage do staying reasonably close to the rhumb line is that you have a built in progress indicator.

Dave
I do not think anyone has suggested that you should CTS method to plan a passage an blindly sail off following that course. If the RYA or any instructor is not advocating plotting checking the ground track that the CTS will follow then they not doing a very good or responsible job of instructing.

If one is doing a multi vector passage plan it is easy to compute or chart the sum of the hourly tides and the distance the boat travels in order to establish a ground track (this will also work if you vary the boat speed for expected conditions when calculating our CTS). Using OpenCPN to this takes barely a minute or two. Once this is done, while I have not yet put it to test I would suggest that following the rhumb lines between these hourly progress waypoints that you have just plotted will still be better than following the rhumb line between the start and end of your passage. If you are advocating using you electronics to follow the rhumb line then why not follow the CTS and validate the tidal set/drift with the tide vector that is being displayed.

If you are crossing a TSS, or other complex situations arise, then once clear and the workload has been reduced it would be both safe and prudent to either recalculate a new CTS or correct back to your planned ground track at an appropriate rate.

I was taught a 7P principle when I was in flight school Proper Prior Planning Prevents Piss Poor Performance. If the prior planning is to use a CTS then a ground track should be evaluated before setting off. Similarly if one is crossing the Channel in spring tides the rhumb line route should be evaluated. Whether one chooses the CTS or the rhumb line, it is their choice based upon their experience. If one needs to stay near a rhumb line to monitor your progress then so be it. If one wants to do a little more preparatory planning then there are more options available, and if something goes wrong, less time adapting to the new situation.
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Old 03-02-2013, 15:55   #123
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Re: Plotting the expected ground track

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Originally Posted by Seaworthy Lass View Post
You're welcome Bill . Really glad that helped to clarify things.

Dockhead and I disagree only slightly I think. He feels in open water where there are no hazards you are not concerned where the current takes you. That is not unreasonable.

I feel though that in this situation if you are not racing, then rather then recomputing the CTS frequently, you can just look at your deviation from the expected ground track that you plotted before you started. You would only then need to recompute if this varied significantly, saving nav work along the way.

When sailing a course surrounded by hazards and if the current is not perpendicular and particularly when it varies in direction, I think (hope, LOL) Dockhead may agree that it is important to plot the expected ground track as this is not intuitive and hazards need to be checked for.
SWL and I don't disagree on this even in the slightest. It's a subject not relevant to figuring out an efficient passage. If you have any doubt about hazards at all, then of course you need to plot a ground track.

But if you have a chart plotter, even this is not really a matter of life or death. You see where you are in relation to hazards in real time. Anyway you need to be keeping an eye on the plotter, with or without a CTS passage, always watching for potential hazards in your path -- it's elementary situational awareness.

If you don't have a chart plotter, then probably you always need to plot your ground track, even if it doesn't seem to you that you will come anywhere near any hazards. But that is elementary situational awareness for paper chart/chart work sailors anyway -- whether or not you're doing a CTS passage.

For my own part -- I always plan all of my passages on paper charts, as much as I love advanced technology. Careful study with paper beforehand will pay big dividends in situational awareness when you're underway - Prior Proper Planning etc.
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Old 03-02-2013, 16:02   #124
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Re: Single CTS or follow the Courseline?

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Originally Posted by LJH View Post
......
I was taught a 7P principle when I was in flight school Proper Prior Planning Prevents Piss Poor Performance.
I just love this expression! Had that drummed into me too LOL. Also to be constantly thinking what steps would be needed if an emergency situation arose. It is far easier to respond instantly if this has been at the back of your mind at all times. Both these principles are so very applicable to sailing as well, particularly when sailing on the edge .
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Old 03-02-2013, 17:28   #125
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Re: Single CTS or follow the Courseline?

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Originally Posted by bewitched View Post
See my post #6. or consider this example:

NCL boat vs CTS boat: Expected wind conditions during passage :
1st hour = light wind reach - expected BSP 6kts
2nd hour = moderate wind reach - expected BSP 7.5kts
3rd hour = fresh breeze reach - expected boat speed 8.5 kts
4th hour - fresh breeze run - expected boat speed 10kts

NCL boat has an average BSP of 8kts

CTS boat, as dictated by the CTS calc must travel at a constant speed. That constant speed must be achievable over the whole course. The only speed achievable over the whole course is 6kts. The CTS boat is therefore restricted to a BSP of 6kts.
I was away for the weekend so I did not have a chance to look at this before this evening. I have There is no reason that a single CTS boat cannot vary speed. In fact if one can plan for it. Applying the speeds above to the CTS boat in your spreadsheet, the CTS boat with the increasing speed will arrive 21 minutes before the CTS boat restricted to 6 Kts.

There is a screen shot of the differences between the scenarios. I have also attached a spreadsheet showing the calculations for each scenario.

Note about the spreadsheet. The paired numbers in pale yellow are the radian angles for Lat and Long. Formulas are based on a spheroid with a radius of 3438 NM. I am not a member of the flat earth society!

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Originally Posted by bewitched View Post
These two issues are the heart of the problem:

1. How do you beat a boat that can sail faster than you?
I am not trying to beat another boat, I am trying to sail as efficiently as I can in mine. But I don't think I am quite as good as my son at that!

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Originally Posted by bewitched View Post
2. How do you gather boat-specific leeway data to such accuracy and then predict what will actually happen during the course of your passage to the same accuracy?
Sail, Sail and Sail. You will get a pretty darn good idea if you sail your boat.

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I put it to the forum that the answer to both these questions in the vast majority of cases will be that you can't.
see above.
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Old 03-02-2013, 17:42   #126
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Re: Single CTS or follow the Courseline?

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Originally Posted by LJH View Post
I was away for the weekend so I did not have a chance to look at this before this evening. I have There is no reason that a single CTS boat cannot vary speed. In fact if one can plan for it. Applying the speeds above to the CTS boat in your spreadsheet, the CTS boat with the increasing speed will arrive 21 minutes before the CTS boat restricted to 6 Kts.

There is a screen shot of the differences between the scenarios. I have also attached a spreadsheet showing the calculations for each scenario.

Note about the spreadsheet. The paired numbers in pale yellow are the radian angles for Lat and Long. Formulas are based on a spheroid with a radius of 3438 NM. I am not a member of the flat earth society!



I am not trying to beat another boat, I am trying to sail as efficiently as I can in mine. But I don't think I am quite as good as my son at that!



Sail, Sail and Sail. You will get a pretty darn good idea if you sail your boat.


see above.
Absolutely!!

Your input in your CTS calculation is your average speed. The fact that you might sail different speeds during different parts of your passage is no problem at all.
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Old 03-02-2013, 19:21   #127
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Re: Single CTS or follow the Courseline?

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OK, here's a proof of sorts. I'm on another computer and can't post a scan of my work, but I'll walk you through it. I am doing this stepwise, treating each hour (or fraction) independently.

First, the easy "crabbing along the rhumbline" solution.

Hour 1: (5 kts BSP, crosscurrent of 2 kts). I didn't bother to work out the CTS angle, but we have a triangle with 2 miles for the current, 5 miles for the CTS, and progress along the rhumbline of 4.583 miles (square root of the sum of the squares).

Hour 2: the triangle is 3 miles (current) 5 miles (CTS) and 4 miles along the rhumbline.

Final 0.7456 hour: the triangle is 1.491 miles (current), 3.728 miles (CTS), and 3.417 miles (along the rhumbline).

The total distance along the rhumbline is 12 miles, the CTS distance is 13.643 miles, and the elapsed time is 2.746 hours.

Now, we see how far we can get in the same time (2.746 hours), with a constant CTS:

Vectors are 6.491 miles (current), 12 miles (rhumbline), and 13.730 miles (CTS, 2.746 hours @ 5 kts). The end of the CTS vector is 0.087 miles *beyond* the destination.

We reach the destination sooner with a constant CTS, than by crabbing. The distance sailed crabbing is longer than the constant CTS distance.

Does anybody see a flaw in my analysis?

Please note that this is purely a math exercise, and this assumes perfect information and performance. But I think this is a good place to start when you are trying to analyze this stuff.

Paul, I just did some quick math on top of yours......using a 40 nm crossing....instead of 12 nm...which might be a typical cruising day for me. ( 3.3 times further.) If the Constant CTS boat gets there 3.3 x sooner than me..that appears to equate to roughly 4 minutes sooner ?

I think that's what you were illustrating.....but I figured I'd extend it a little.
I often lose 4 minutes catching a fish so 4 minutes doesn't really upset me, because I'm not racing; but if I were it could mean I'd be having a beer while watching the rest of the fleet come in. So, good stuff!

I apologize if I'm chiming in very late in this conversation, It's taken me about 2 days to read and absorb all this. I for one would like to thank all the contributors of this thread...for a very respectful and educational dialogue, And thanks to SWL for a well thought out and presented alternative to solving set and drift problems.
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Old 03-02-2013, 22:42   #128
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Re: Is there a THIRD WAY alternative? ("Middle Way")

Why not take the best out of both the main schools, in cases where it makes no sense to stick to a straight path across the ground ("crabbing along the rhumb"):

Here's what I'm thinking:

Work out a CTS using the best tidal data you have, and plot the theoretical ground track which would result from steering it.

Make the usual 'step-change' assumption, that the tide is constant during each hour (or half hour, if you have better data)

The result will be the series of straight lines we're familiar with from SwL's plots of ground track. It's just not that difficult.
Check it keeps you well away from dangers.

Then set a GPS waypoint at each kink in that theoretical ground track (eg hourly)

Now "crab along" each hourly "rhumbline" between successive waypoints, using the GPS.
Your heading will always be roughly what you calculated, if the data are good.

If the data predict current reality perfectly (unlikely, given their "step change" nature) then your heading (or more pedantically, the reciprocal of your wake bearing) will be exactly as calculated, for the entire duration.

What if the data are somewhat inaccurate but correct in 'character'?

(In other words, the current vector diagram is recognisably similar in shape and size to a diagram drawn with perfect foreknowledge)

Surely you're still way better off, in any case where that diagram is big enough and meandering enough to justify a CTS strategy in the first place, than the person crabbing along the single straight rhumbline.

If you have to make a course correction to avoid an unplanned obstacle, you would simply continue heading for the next waypoint. No drama; and no need to sidle back onto the mini-rhumb, unless you would otherwise pass unacceptably near to a danger

It seems to me that with this method you're largely immunised from problems with the data, unless these problems are so severe that

a) you probably shouldn't be attemping the passage at all with the data you have*, and

b) Crabbing along a single rhumbline would simply not get you there.


I wouldn't bother recalculating the intended ground track unless the boat's heading was wildly at variance with the CTS figure: and the first thing I would suspect would be my calculations or plot.

If these were OK, I'd check I'd entered the waypoints correctly, and if no problems there, I'd reconsider the plan, possibly involving abandoning the projected arrival point in favour of a more achievable one, or even turning back.

If I arrived at particular waypoint twenty minutes early or late, I'd certainly be reviewing the plan: it would suggest a major component of tide with or against the CTS was very different from what the data predicted.


* (unless it's entirely free of dangers, or other special circumstances: eg you are greatly slowed because you're towing a dispensable load, you're trying to conserve a small reserve of fuel, you're trying not to arrive at the beginning of a tide race too early ..... in circumstances, generally, where you can "put the hammer down" and greatly exceed the target boatspeed, AND at least match the maximum current speed, if things get ugly)
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Old 04-02-2013, 02:54   #129
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Re: Single CTS or follow the Courseline?

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Originally Posted by Tempest245 View Post
Paul, I just did some quick math on top of yours......using a 40 nm crossing....instead of 12 nm...which might be a typical cruising day for me. ( 3.3 times further.) If the Constant CTS boat gets there 3.3 x sooner than me..that appears to equate to roughly 4 minutes sooner ?

I think that's what you were illustrating.....but I figured I'd extend it a little.
I often lose 4 minutes catching a fish so 4 minutes doesn't really upset me, because I'm not racing; but if I were it could mean I'd be having a beer while watching the rest of the fleet come in. So, good stuff!

I apologize if I'm chiming in very late in this conversation, It's taken me about 2 days to read and absorb all this. I for one would like to thank all the contributors of this thread...for a very respectful and educational dialogue, And thanks to SWL for a well thought out and presented alternative to solving set and drift problems.
Indeed, the example posed by Lodesman is one where there is little benefit to a CTS passage.

If there is no current or a very consistent current, then there's no point to calculating a CTS and you might as well put your pilot on "track mode", or fudge a couple of degrees for the one knot increase in the middle.

CTS techniques are needed only where there are strong currents relative to your boat speed, and/or a big difference in currents over the course of your passage.

Many coastal sailors never encounter such conditions, which is why they are unfamiliar with the method.
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Old 04-02-2013, 03:01   #130
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Re: Is there a THIRD WAY alternative? ("Middle Way")

Quote:
Originally Posted by Andrew Troup View Post
Why not take the best out of both the main schools, in cases where it makes no sense to stick to a straight path across the ground ("crabbing along the rhumb"):

Here's what I'm thinking:

Work out a CTS using the best tidal data you have, and plot the theoretical ground track which would result from steering it.

Make the usual 'step-change' assumption, that the tide is constant during each hour (or half hour, if you have better data)

The result will be the series of straight lines we're familiar with from SwL's plots of ground track. It's just not that difficult.
Check it keeps you well away from dangers.

Then set a GPS waypoint at each kink in that theoretical ground track (eg hourly)

Now "crab along" each hourly "rhumbline" between successive waypoints, using the GPS.
Your heading will always be roughly what you calculated, if the data are good.

If the data predict current reality perfectly (unlikely, given their "step change" nature) then your heading (or more pedantically, the reciprocal of your wake bearing) will be exactly as calculated, for the entire duration.

What if the data are somewhat inaccurate but correct in 'character'?

(In other words, the current vector diagram is recognisably similar in shape and size to a diagram drawn with perfect foreknowledge)

Surely you're still way better off, in any case where that diagram is big enough and meandering enough to justify a CTS strategy in the first place, than the person crabbing along the single straight rhumbline.

If you have to make a course correction to avoid an unplanned obstacle, you would simply continue heading for the next waypoint. No drama; and no need to sidle back onto the mini-rhumb, unless you would otherwise pass unacceptably near to a danger

It seems to me that with this method you're largely immunised from problems with the data, unless these problems are so severe that

a) you probably shouldn't be attemping the passage at all with the data you have*, and

b) Crabbing along a single rhumbline would simply not get you there.


I wouldn't bother recalculating the intended ground track unless the boat's heading was wildly at variance with the CTS figure: and the first thing I would suspect would be my calculations or plot.

If these were OK, I'd check I'd entered the waypoints correctly, and if no problems there, I'd reconsider the plan, possibly involving abandoning the projected arrival point in favour of a more achievable one, or even turning back.

If I arrived at particular waypoint twenty minutes early or late, I'd certainly be reviewing the plan: it would suggest a major component of tide with or against the CTS was very different from what the data predicted.


* (unless it's entirely free of dangers, or other special circumstances: eg you are greatly slowed because you're towing a dispensable load, you're trying to conserve a small reserve of fuel, you're trying not to arrive at the beginning of a tide race too early ..... in circumstances, generally, where you can "put the hammer down" and greatly exceed the target boatspeed, AND at least match the maximum current speed, if things get ugly)
Very clever! A lot of original ideas have come out of the three recent threads on these questions.

I think this technique would work quite well. I would not use it myself, as it gives up a little efficiency, a sacrifice unnecessary if you are comfortable with regular CTS techniques. But the cost in efficiency would be pretty small, and if it's really important to you to have a very easy and instant picture of your ground track, then maybe worthwhile for someone.

Keep in mind that all your waypoints would change if you get ahead or fall behind schedule, so there's no advantage there, compared to a regular CTS technique. Just like with regular CTS, you would have to rerun the whole passage if you get off plan - you can't just keep doggedly chasing the same old hourly waypoints.

It would be interesting to see a mathematical comparison with regular CTS and rhumbline crabbing. I bet it will be quite close to regular CTS
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Old 04-02-2013, 07:37   #131
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Re: Is there a THIRD WAY alternative? ("Middle Way")

Quote:
Originally Posted by Andrew Troup View Post
Why not take the best out of both the main schools, in cases where it makes no sense to stick to a straight path across the ground ("crabbing along the rhumb"):

Here's what I'm thinking:

Work out a CTS using the best tidal data you have, and plot the theoretical ground track which would result from steering it.

Make the usual 'step-change' assumption, that the tide is constant during each hour (or half hour, if you have better data)

The result will be the series of straight lines we're familiar with from SwL's plots of ground track. It's just not that difficult.
Check it keeps you well away from dangers.

Then set a GPS waypoint at each kink in that theoretical ground track (eg hourly)

Now "crab along" each hourly "rhumbline" between successive waypoints, using the GPS.
Your heading will always be roughly what you calculated, if the data are good.

If the data predict current reality perfectly (unlikely, given their "step change" nature) then your heading (or more pedantically, the reciprocal of your wake bearing) will be exactly as calculated, for the entire duration.

What if the data are somewhat inaccurate but correct in 'character'?

(In other words, the current vector diagram is recognisably similar in shape and size to a diagram drawn with perfect foreknowledge)

Surely you're still way better off, in any case where that diagram is big enough and meandering enough to justify a CTS strategy in the first place, than the person crabbing along the single straight rhumbline.

If you have to make a course correction to avoid an unplanned obstacle, you would simply continue heading for the next waypoint. No drama; and no need to sidle back onto the mini-rhumb, unless you would otherwise pass unacceptably near to a danger

It seems to me that with this method you're largely immunised from problems with the data, unless these problems are so severe that

a) you probably shouldn't be attemping the passage at all with the data you have*, and

b) Crabbing along a single rhumbline would simply not get you there.


I wouldn't bother recalculating the intended ground track unless the boat's heading was wildly at variance with the CTS figure: and the first thing I would suspect would be my calculations or plot.

If these were OK, I'd check I'd entered the waypoints correctly, and if no problems there, I'd reconsider the plan, possibly involving abandoning the projected arrival point in favour of a more achievable one, or even turning back.

If I arrived at particular waypoint twenty minutes early or late, I'd certainly be reviewing the plan: it would suggest a major component of tide with or against the CTS was very different from what the data predicted.


* (unless it's entirely free of dangers, or other special circumstances: eg you are greatly slowed because you're towing a dispensable load, you're trying to conserve a small reserve of fuel, you're trying not to arrive at the beginning of a tide race too early ..... in circumstances, generally, where you can "put the hammer down" and greatly exceed the target boatspeed, AND at least match the maximum current speed, if things get ugly)
Andrew,
You've given an excellent description of what I envisaged at (a) when I asked the question. I think if I should ever find a need to follow a single CTS for multiple currents, I will do it this way.
Quote:
Do you: (a) plot the expected CMG for each tidal set and change course to maintain that?;
(b) take periodic fixes and recalculate a new CTS based on previously-planned and possibly incorrect tidal data;
(c) take periodic fixes and recalculate a new CTS based on tidal data adjusted by observation;
(d) stick to the planned CTS with faith that it will all even out by the end, fixing and running DRs/EPs to ensure navigational safety;
(e) stick to the planned CTS and only pansies fix; or
(f) other?
Edit to comment on Dockhead's points - I agree it will eat into the efficiency, which is why I asked the question originally. I think that fine-tuning minor variances in the set would not affect the plan any more than large corrections that would otherwise be required by "regular CTS technique." If "wildly" large corrections are required, it would only be because the tidal set information is way out. If that was the case, it would not likely be possible to continue a single-CTS plan, as you would not know what set to base it upon; and you would have to revert to 'fix and EP'.
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Old 04-02-2013, 09:49   #132
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Re: Single CTS or follow the Courseline?

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Originally Posted by Dockhead View Post
Indeed, the example posed by Lodesman is one where there is little benefit to a CTS passage.

If there is no current or a very consistent current, then there's no point to calculating a CTS and you might as well put your pilot on "track mode", or fudge a couple of degrees for the one knot increase in the middle.

CTS techniques are needed only where there are strong currents relative to your boat speed, and/or a big difference in currents over the course of your passage.

Many coastal sailors never encounter such conditions, which is why they are unfamiliar with the method.
It's not so much that we don't encounter them, or are unfamiliar with the methods. a 3 kn. cross current in a sailboat that avgs. 5kn ttw is fairly substantial over time. It's just that coastal trip planning is more often about timing your arrival at a destination to take advantage of a slack or favorable current X hours hence. Or, setting out with a outgoing tide that clears you of land. The extreme currents usually do take place in narrow passes or rivers where they're often either ahead or astern. ( coastal)

The strategy for ocean currents like the gulf stream that can run 5+ knots in one direction is to either find the best spot to cross them as quickly as possible and/or pick up an eddy that runs counter to it and get a little slingshot effect. There's no strategy that I can employ to sail against it; at best, I hope to not lose ground in the crossing by keeping my boat speed up. ( Incentive for a bigger boat? )

Though, I've never done it; I understand the strategy to go from San Diego to Vancouver is to sail to Hawaii, rather than try to head into the California current.

Other than the major ocean currents that are known and the coastal tides and currents that are largely predicted, one is left with open ocean where you're making constant adjustments to the conditions and looking for favorable winds.

This is not to say, that I don't appreciate the elegant mathematical solution of trying to determine a constant course to steer over multiple tidal changes. I just don't know yet where I'd employ it. But, I've printed the methods and instructions for experimenting.
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Old 04-02-2013, 10:20   #133
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Re: Is there a THIRD WAY alternative? ("Middle Way")

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Originally Posted by Lodesman View Post
Andrew,
You've given an excellent description of what I envisaged at (a) when I asked the question. I think if I should ever find a need to follow a single CTS for multiple currents, I will do it this way.


Edit to comment on Dockhead's points - I agree it will eat into the efficiency, which is why I asked the question originally. I think that fine-tuning minor variances in the set would not affect the plan any more than large corrections that would otherwise be required by "regular CTS technique." If "wildly" large corrections are required, it would only be because the tidal set information is way out. If that was the case, it would not likely be possible to continue a single-CTS plan, as you would not know what set to base it upon; and you would have to revert to 'fix and EP'.
You will have very small course changes from waypoint to waypoint using Andrew's method, because you are almost sailing a regular constant heading course. The lost efficiency will be very small. I would say that for anyone who is more comfortable calculating it like this, there's hardly any argument against it. I wouldn't use it because it would be quite a lot more work than the way I do it, for me anyway.

If you get off plan using Andrew's method, you have to throw all the waypoints out and start all over again, just like you have to do with a regular CTS approach.

You will have an excellent overview of your ground track -- the one big advantage of Andrew's method, although you do need to keep in mind that the predicted ground track is out the window if you get off plan.

Yet another, even simpler version of Andrew's method might be not to use hourly waypoints at all, but just sail to one intermediate waypoint which is calculated to put you reasonably uptide of your destination when you get there. Even this would be enormously much better than a rhumb line passage, in many cases.


But one aspect of the classical CTS method which is unquantifiable, and is not a matter of efficiency at all, is this -- when it comes off well, it simply feels so cool that you had the skill to do the numbers right and as a result, you just arced right into your destination hardly having touched your helm. It is really incredibly satisfying -- the power of navigation and your own skill over the chaos of moving water -- something like the feeling after a well-executed tack or a well-executed docking maneuver -- one of the joys of sailing.
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Old 04-02-2013, 12:45   #134
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Re: Single CTS or follow the Courseline?

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Originally Posted by Tempest245 View Post
It's not so much that we don't encounter them, or are unfamiliar with the methods. a 3 kn. cross current in a sailboat that avgs. 5kn ttw is fairly substantial over time. It's just that coastal trip planning is more often about timing your arrival at a destination to take advantage of a slack or favorable current X hours hence. Or, setting out with a outgoing tide that clears you of land. The extreme currents usually do take place in narrow passes or rivers where they're often either ahead or astern. ( coastal)

The strategy for ocean currents like the gulf stream that can run 5+ knots in one direction is to either find the best spot to cross them as quickly as possible and/or pick up an eddy that runs counter to it and get a little slingshot effect. There's no strategy that I can employ to sail against it; at best, I hope to not lose ground in the crossing by keeping my boat speed up. ( Incentive for a bigger boat? )

Though, I've never done it; I understand the strategy to go from San Diego to Vancouver is to sail to Hawaii, rather than try to head into the California current.

Other than the major ocean currents that are known and the coastal tides and currents that are largely predicted, one is left with open ocean where you're making constant adjustments to the conditions and looking for favorable winds.

This is not to say, that I don't appreciate the elegant mathematical solution of trying to determine a constant course to steer over multiple tidal changes. I just don't know yet where I'd employ it. But, I've printed the methods and instructions for experimenting.
I have done that trip and that's what I was told, but going to Hawaii seemed ridiculous. Took me 21 days versus the (optimistic plan) 30 days @ 6 knots via Hawaii (though the Hawaii route would have been a good excuse to swan about in the owners boat -maybe THAT'S what they meant )

Perhaps the current lengthened the swell's period and lowered the amplitude and allowed me better progress in strong wind....

I don't exactly have a good dog in this hunt either, but my mongrel is getting some exercise.
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Old 04-02-2013, 13:14   #135
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Re: Single CTS or follow the Courseline?

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Though, I've never done it; I understand the strategy to go from San Diego to Vancouver is to sail to Hawaii, rather than try to head into the California current.

I know folks who tried the direct route unsuccessfully and one who managed it. He said it was one of the worst experiences he has had. This issue is probably more wind related than current related. It is a beat in the prevailing winds.
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