Chartplotter - Course To Steer (CTS)

Jokani

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I am disappointed to find out that a Garmin GPSMAP 7408xsv cannot display a Course To Steer (CTS).

I found this surprising as it can display Bearing To Waypoint (BTW), Set and Drift.

Were my expectations unrealistic, are other Garmin models or makes able to display a CTS, or is is simply not possible to calculate a CTS?
 

prv

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As far as I know (and I could be wrong) there are no hardware plotters that will calculate a net course to steer across predicted tides (eg the classic S-curve across the Channel). There are PC navigation programs that will do it.

For shorter legs where one can assume a constant tide, you just put the predicted track line on your destination and keep it there :)

Pete
 

johnalison

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You need an old Navstar Decca, which used to do this nicely you plumbed in the tide rate and direction. My Raymarine plotter doesn't. I just take the bearing to waypoint and add/subtract 0, 5 or 10 degrees as my mood suits.
 

Pagetslady

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My C120 does this after a fashion by putting the autopilot into track to a waypoint and it keeps the XTE spot on, but it does not calculate the CTS. This would not be the best way to cross the channel or anywhere else where you get tides on the beam from both sides over a single passage.
 

KellysEye

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> a net course to steer across predicted tides (eg the classic S-curve across the Channel)

As far as I know a cross channel course is sailed as a straight line but because of the tides it beomes an S-curve.
 

prv

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As far as I am aware the compass only enhances radar features.

I'm not particularly familiar with Garmin kit, but I'd expect it to also enable a heading line on the screen to go with the track one from GPS. So on my middle-aged Raymarine I have a red line showing where the bow is pointing, and a green line showing where the boat is traveling. Motoring in still water they coincide, sailing with little wind in a strong tide they can be wildly different. As I said above, the plotter equivalent of a calculated course to steer (for a short leg where we can assume the tide won't change much) is to simply put the green line over the destination and steer to keep it there - I find it useful to also have the red line to show visually how much effect the tide is having.

Pete
 

Robin

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Which PC programmes will do this?

I used to have Neptune Passage Planner back in the UK, excellent and I think a forum member here did a simple one for Channel crossings ( Danny labrador???) Otherwise plotters may have tidal height data loaded but not streams. Those of us oldies that learned 'proper nav' will do it wiv a pencil, tidal atlas and paper, not difficult. .
 

Robin

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I took a advantage of a Boat Show special offer and purchased a 'Garmin Marine Heading Sensor'.

Garmin Support have confirmed that adding a heading sensor/compass, will not enable the GPSMAP calculate/display will a CTS.

As far as I am aware the compass only enhances radar features.

+1, we have Garmin full network with wind,Heading sensor, radar and AIS. We can always set a route up and put the Raymarine Pilot on it's 'track' function but that is just continual correction of off track error AFIK.
 

prv

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Otherwise plotters may have tidal height data loaded but not streams.

They often do have predicted streams as well, but not the software to work out a net stream over a predicted passage and turn it into a course to steer.

I suspect in most of their global market there isn't much call for this. It's really only needed for passages of about the width of the English Channel in places with strongish tides. Obviously with weak or non-existent tides you don't need to worry about it, with short passages you won't lose much by treating the tide as constant and just matching COG with BTW (or putting the green line on the destination), and I assume that people crossing greater distances don't bother trying to compute a CTS for the whole passage because the inaccuracies compound to make it pointless.

Pete
 

RichardS

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I'm not particularly familiar with Garmin kit, but I'd expect it to also enable a heading line on the screen to go with the track one from GPS. So on my middle-aged Raymarine I have a red line showing where the bow is pointing, and a green line showing where the boat is traveling. Motoring in still water they coincide, sailing with little wind in a strong tide they can be wildly different. As I said above, the plotter equivalent of a calculated course to steer (for a short leg where we can assume the tide won't change much) is to simply put the green line over the destination and steer to keep it there - I find it useful to also have the red line to show visually how much effect the tide is having.

Pete

Over the years I've also played around with those lines on my Raymarine Classic but, being in the Med, I settled on just showing the green COG projection as that shows what we will actually hit! I've never found a way to scroll along the course but still have the green line visible as the line vanishes as soon as the boat goes off screen which is a pity so you have to zoom out to follow the projection and then you lose the detail.

Richard
 

Robin

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They often do have predicted streams as well, but not the software to work out a net stream over a predicted passage and turn it into a course to steer.

I suspect in most of their global market there isn't much call for this. It's really only needed for passages of about the width of the English Channel in places with strongish tides. Obviously with weak or non-existent tides you don't need to worry about it, with short passages you won't lose much by treating the tide as constant and just matching COG with BTW (or putting the green line on the destination), and I assume that people crossing greater distances don't bother trying to compute a CTS for the whole passage because the inaccuracies compound to make it pointless.

Pete

The septics we talk to hereabouts have absolutely no idea of planning to allow for tidal streams. They cross the Gulf Stream ( unidirectional but rate varies) by the simple 'go to' method and go, although the pilot guides gove some idea of corrections to apply from various start points to cross from Florida to Bahamas. Maybe up north or in the Pacific North West they have a better understanding. There have been multiple argumentative threads about this on Cruisers Forum, not helped by lots of big engined mobos members really not understanding things from a sail boat speed perspective. let alone wind direction complications.:ambivalence:
 

prv

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The septics we talk to hereabouts have absolutely no idea of planning to allow for tidal streams.

That's been the impression I get, and why I think the plotter manufacturers have little interest in providing this kind of function. Several books and blogs by Americans describe trepidation at visiting our tide-wracked waters and having to think about such things for the first time.

As you say, the US is a big place so I assume there are sailors in some parts of it who have to "do" tides - but they seem to be a small minority.

Pete
 

prv

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I've never found a way to scroll along the course but still have the green line visible as the line vanishes as soon as the boat goes off screen which is a pity so you have to zoom out to follow the projection and then you lose the detail.

Yep - pain in the bum :)

I often find myself wanting to set a zoom level where the boat is currently just off the edge of the screen but the destination is on-screen, and I want to see the green line sitting over it. But I have to zoom out so that both are visible, which usually gives less detail at the destination than I would like.

Pete
 
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