Course to steer software

[Hugh_Poore]

Does anyone know of a charting software that enables construction of a Course to Steer. The software wild need to have tidal information to do this. Eg cant do a course to steer with Navionics.

[s/v Jedi]

Originally Posted by Hugh_Poore

Does anyone know of a charting software that enables construction of a Course to Steer. The software wild need to have tidal information to do this. Eg cant do a course to steer with Navionics.

You mean drive the autopilot? OpenCPN on laptop or iSailor on iPad is what I used successfully for that.

[muttnik]

Originally Posted by s/v Jedi

You mean drive the autopilot? OpenCPN on laptop or iSailor on iPad is what I used successfully for that.

I may be misinterpreting your reply but I think Hugh_Poore is talking about calculating a course to steer which is rather a different thing to getting software to drive the autopilot to a way point.

In other words, you're doing a multi-hour passage where current will vary at different points in different ways according to your time of departure and anticipated speed. Hit "Go to waypoint" and rely on GPS and your distance through the water will be somewhat further than if you account for current effects and calculate a single course to steer for the whole passage.

Software would need to know about currents, tides, time of departure and expected speed. Doubtless super-fancy high end software could factor in gribs, polars, sea state etc to calculate anticipated speed and leeway but that might be expecting too much and not be accurate enough to justify the complexity involved.

...which you may have meant in your reply and I may have misinterpreted the misinterpretation (apologies if so) and OpenCPN may be able to do that but I didn't know it could. Certainly Navionics can't do it and neither can my raymarine plotter but actually this is the kind of manual Nav I kind of enjoy doing by hand anyway

[s/v Jedi]

Originally Posted by muttnik

I may be misinterpreting your reply but I think Hugh_Poore is talking about calculating a course to steer which is rather a different thing to getting software to drive the autopilot to a way point.

In other words, you're doing a multi-hour passage where current will vary at different points in different ways according to your time of departure and anticipated speed. Hit "Go to waypoint" and rely on GPS and your distance through the water will be somewhat further than if you account for current effects and calculate a single course to steer for the whole passage.

Software would need to know about currents, tides, time of departure and expected speed. Doubtless super-fancy high end software could factor in gribs, polars, sea state etc to calculate anticipated speed and leeway but that might be expecting too much and not be accurate enough to justify the complexity involved.

...which you may have meant in your reply and I may have misinterpreted the misinterpretation (apologies if so) and OpenCPN may be able to do that but I didn't know it could. Certainly Navionics can't do it and neither can my raymarine plotter but actually this is the kind of manual Nav I kind of enjoy doing by hand anyway

No my assumption was wrong and I think you’re right. I’ve always done this using the rule of 12ths and add corrections for drift due to wind and waves. It’s been a long time ago when I sailed through reversing tides so I never missed that feature in software. Even when tidal info is available (which it is in all software I think) then you still need to adjust for drift.

[CassidyNZ]

As Jedi alluded to, most nav software will present current (mostly tidal) on the charts. But then one has to factor in leeway (mostly for sailing boats) as well. I wonder firstly if there is affordable software that will do that and secondly if that isn’t one of the fundamentals of pilotage that should accompany visual input of one’s surroundings.

On paper charts these calcs and the visual representations of them were quite easy, I’ve never actually tried doing it on Navionics. I guess it’s possible but I just have a look at the data and wing it from there.

Tidal drift info on Navionics shown on the attachment at bottom of the image.

[Jim Cate]

This sort of detailed tidal current info is just not available in most of the world, so most of us just have to wing it when crossing tidal streams. In most cases the increased distance travel ed isn't all that much, so it isn't a big deal.

I suspect that crossing from England to France, a voyage across a really vigorous reversing tidal flow, one that is very well annotated, is the major place where course to steer calculations are used (and why the YRA exams spend so much time on the subject). So, perhaps that is why no one has developed the software to automate the process.

There was a lengthy thread about means of doing the calculations here on CF a few years back, and some innovative solutions were developed, but not software methods.

Jim

[s/v Jedi]

Originally Posted by Jim Cate

This sort of detailed tidal current info is just not available in most of the world, so most of us just have to wing it when crossing tidal streams. In most cases the increased distance travel ed isn't all that much, so it isn't a big deal.

I suspect that crossing from England to France, a voyage across a really vigorous reversing tidal flow, one that is very well annotated, is the major place where course to steer calculations are used (and why the YRA exams spend so much time on the subject). So, perhaps that is why no one has developed the software to automate the process.

There was a lengthy thread about means of doing the calculations here on CF a few years back, and some innovative solutions were developed, but not software methods.

Jim

The most remarkable course correction I encountered is the passage Lowestoft UK <> IJmuiden NL. This is a 100nm passage heading exactly East or West, with a strong tidal current setting North or South depending on tide. The correction is 0 degrees because you spend as much time being set south as being set North

[stormalong]

There is really no need for this calculation. Just set up your GPS or chart plotter to steer to a waypoint and correct for off track error as you go. The current changes so rapidly that any calculation would need redoing every few minutes. Even if you could get accurate tide data you would need a time and course spreadsheet.

[Hugh_Poore]

Originally Posted by muttnik

I may be misinterpreting your reply but I think Hugh_Poore is talking about calculating a course to steer which is rather a different thing to getting software to drive the autopilot to a way point.

In other words, you're doing a multi-hour passage where current will vary at different points in different ways according to your time of departure and anticipated speed. Hit "Go to waypoint" and rely on GPS and your distance through the water will be somewhat further than if you account for current effects and calculate a single course to steer for the whole passage.

Software would need to know about currents, tides, time of departure and expected speed. Doubtless super-fancy high end software could factor in gribs, polars, sea state etc to calculate anticipated speed and leeway but that might be expecting too much and not be accurate enough to justify the complexity involved.

...which you may have meant in your reply and I may have misinterpreted the misinterpretation (apologies if so) and OpenCPN may be able to do that but I didn't know it could. Certainly Navionics can't do it and neither can my raymarine plotter but actually this is the kind of manual Nav I kind of enjoy doing by hand anyway

Yes thanks for this. You are quite right. I teach RYA Day Skipper and Yachtmaster theory. The idea is to show students after they have done calculations on a chart how they can do something similar using technology. For example using in-built tidal stream information to produce an overall course to steer.

Most users of chart plotting software believe that all you have to do is monitor your XTE and keeping adjusting your course. It is a very inefficient way if travelling between 2 points.

It can be alot of fun understanding tidal streams and creating a course to steer as part of overall passage planning.

SOLAS Regs Chapter 5 require that we all construct a passage plan before leaving the harbour.

Anyway still on the hunt for the software. Savvy Navvy might be good but I have yet to try it.

[Hugh_Poore]

Originally Posted by stormalong

There is really no need for this calculation. Just set up your GPS or chart plotter to steer to a waypoint and correct for off track error as you go. The current changes so rapidly that any calculation would need redoing every few minutes. Even if you could get accurate tide data you would need a time and course spreadsheet.

Understanding tidal streams can be very useful in passage planning. For example, making sure we have the tide with us or that we dont have wind against tide making for a rough crossing. Constructing a course to steer is a much more efficient way of travelling between 2 points rather than adjusting periodically for XTE. Normally, tidal stream data is based on hour by hour changes and therefore through pre planning it would be possible to construct a course to steer in about 20 minutes for say a 3 hour journey. Pre planning for any voyage is a requirement under SOLAS Regs but also good seamanship.

[Jim Cate]

SOLAS Regs Chapter 5 require that we all construct a passage plan before leaving the harbour.

Could you please elaborate on this statement? I was not aware of such a requirement for recreational sailing.

And just how inefficient is steering to minimum XTE? I understand the theory, but haven't done the calculations to see just how important this is, even under the unusual conditions of a cross-channel passage. Are we talking a few percent of time wasted or some significant amount?

Jim

[nigel1]

There is this
Neptune Navigation Software


However, it is limited to UK waters.

[Hugh_Poore]

Originally Posted by Jim Cate

Could you please elaborate on this statement? I was not aware of such a requirement for recreational sailing.

And just how inefficient is steering to minimum XTE? I understand the theory, but haven't done the calculations to see just how important this is, even under the unusual conditions of a cross-channel passage. Are we talking a few percent of time wasted or some significant amount?

Jim

Hi Jim, have a look at this link regarding regulations.
Regarding XTE course adjustment v Course to Steer I would say if you have a 2 knot tide pushing you sideways and you are on a passage of some hours the difference could be significant in terms of the overall distance travelled. https://www.google.com/url?sa=t&sour...yD1b0hVfT1BXZB

[Hugh_Poore]

Thanks Nigel, I will have look.

Originally Posted by nigel1

There is this
Neptune Navigation Software


However, it is limited to UK waters.

[stormalong]

Originally Posted by Hugh_Poore

Hi Jim, have a look at this link regarding regulations.
Regarding XTE course adjustment v Course to Steer I would say if you have a 2 knot tide pushing you sideways and you are on a passage of some hours the difference could be significant in terms of the overall distance travelled. https://www.google.com/url?sa=t&sour...yD1b0hVfT1BXZB

Of course adverse current of any kind will impede your progress. You didn't ask that question. You asked for software to calculate a course taking current into consideration.

I cruise in a very strong tidal area. The day before any run I look at the tide graph for the next day to decide when to leave. Sometimes that means an early morning or late afternoon departure and will affect the day's distance traveled. That is basic trip planning. Going from point to point still requires constant course adjustment to stay on the rhumb line and correcting cross track error does just that. These days most of my cruising is in channels of varying widths. No charting software is going to be able to predict the strength of the current in that channel or what position in that channel will have the most adverse current. GPS speed over ground and cross track error are the only practical methods of navigating these channels.