Course to steer for crossing the channel

Well last night I had gone off the idea but after a day of virtual sailing and forumming I'm more optimistic..... All depends on how my family/crew are feeling too .......We've all got to be happy. Just under six months to get ready and jinx the forecast......
 
FairweatherDave said:
My question is what use is there for the GPS other than for keeping an hourly log?
Click to expand...
I can think of several uses for the GPS:
  • Collect data about the crossing;
  • Working out your Speed over the ground;
  • Working out the velocity made good; the best bit in my opinion
  • Working out the ETA; and
  • Computing your average speed
Enjoy your trip and the first beer on the other side.

My usual landfall in France is usually Roscoff and is a 24 hour passage from the Exe. I enjoy plotting the EP for each hour and seeing how close we are to it (assuming we get out of bed at the appointed hour and not miss the tide).
 
Out of the Needles, turn left, keep it between 180-200 (that's about as acurate as anyone can steer) and then see where you are when you get sight of France.
 
Bobc said:
Out of the Needles, turn left, keep it between 180-200 (that's about as acurate as anyone can steer) and then see where you are when you get sight of France.
Click to expand...

The beauty of this is that it works from the Nab as well. The most important thing is to ensure you are uptide of Cherbourg when you get there. It's a 14-16 hour passage for me (12-14 from the Needles) and you sure as fate won't want to punch the channel tide to make landfall.
 
FairweatherDave said:
Have I got it right that as I don't subscribe to Navionics my tidal information has to come from other sources.
Click to expand...
Not as far as I understand it

My subscription has lapsed but I think all I am giving up is chart updates (which I have understood to be new wrecks, changes of buoy positions, new wind farms ...)

I seem to have fully functioning tidal data
 
Bathdave said:
Not as far as I understand it

My subscription has lapsed but I think all I am giving up is chart updates (which I have understood to be new wrecks, changes of buoy positions, new wind farms ...)

I seem to have fully functioning tidal data
Click to expand...

Excellent. I shall have to play with it a bit harder!! 95% much of my sailing doesn't use Navionics
 
Sandy said:
I can think of several uses for the GPS:
  • Collect data about the crossing;
  • Working out your Speed over the ground;
  • Working out the velocity made good; the best bit in my opinion
  • Working out the ETA; and
  • Computing your average speed
Enjoy your trip and the first beer on the other side.

My usual landfall in France is usually Roscoff and is a 24 hour passage from the Exe. I enjoy plotting the EP for each hour and seeing how close we are to it (assuming we get out of bed at the appointed hour and not miss the tide).
Click to expand...

Thanks Sandy. I was being a bit provocative! At the same time I don't have my log impeller in the water too often so I was thinking things through. I use my GPS a lot. But I'm used to a series of waypoints which in this circumstance doesn't really work. I am curious about velocity made good. Is that purely to decide the optimum tack at the time?
 
And factor in the course adjustments for keeping as near to 90 degrees as practical when crossing the shipping lanes. It is surprising how tidal drift can change the angle of crossing the lanes.
Take care in the small area between the shipping lanes - last year a fishing boat (French) who was NOT fishing crossed very, very closely in front of us (port to stbd) despite our being the stand-on vessel even if we weren't sailing (which we were).He had his AIS transponder switched off as well. By the time we had got our camera he was too far away to capture the details.
 
FairweatherDave said:
Well last night I had gone off the idea but after a day of virtual sailing and forumming I'm more optimistic..... All depends on how my family/crew are feeling too .......We've all got to be happy. Just under six months to get ready and jinx the forecast......
Click to expand...
Don't worry. I've been crossing the North Sea and Channel for forty years this year and I still spend all winter fretting about it. As for the family, learn to bluff.
 
Haven’t heard of the “S” shape ground track of which you speak. Maybe because it ‘s a feature of sailing and I use a motor!
You may be confusing the navigation issue too much.
Calculating a course to steer is so you can make good your planned navigational track.
Putting a line on the chart as a guide and then using EP to see your position relative to that is a completely different thing.
Both are good as long as you know which you are doing.

A good tip on arrival from previous posters to arrive with tidal stream in your favour. Also if making land fall on a coastline with poor nav features it may be a good idea to purposely aim to east/ west etc of your chosen arrival. Then on making landfall at least you know which direction your intended destination is.
 
FairweatherDave said:
My question is what use is there for the GPS other than for keeping an hourly log?
Click to expand...

That's pretty-much it. Just stick a mark on the chart every hour, so you have an idea of where you are incase you lose your GPS and need to start using DR. If you steer a constant course, you'll see the nice S shape appear befor your very eyes on the chart.
 
East Cardinal said:
Haven’t heard of the “S” shape ground track of which you speak. Maybe because it ‘s a feature of sailing and I use a motor!
You may be confusing the navigation issue too much.
Click to expand...

Not confusing it at all. Suspect you need to do a basic course in navigation in tidal waters to understand what an S curve COG is. If you did a cross channel (and therefore cross tide) passage even under motor your track would not follow a straight line but would be influenced by the tide. Not a big deal if you are cruising at 20 knots as you only have 3 hours or so of tidal influence on a 60 odd mile passage, However in a sailing boat at 5 knots your passage time is over 12 hours or a full tidal cycle so you will be pushed one way and then the other so your track will be S shaped over the ground. As the tide is stronger on one side of the channel than the other you need to work out (as the OP has done) the net effect of the tide over the duration of the passage so that you can steer a course that takes into account the effect of the tide.

Nothing clever or magic about it, just a bit of work to work out the tidal effect for each hour of the planned passage, plotting regular positions to check progress and making any adjustment when you get closer to your destination to ensure you arrive upwind and tide. As you see from the various posts this method is just about universal.
 
East Cardinal said:
Haven’t heard of the “S” shape ground track of which you speak. Maybe because it ‘s a feature of sailing and I use a motor!
You may be confusing the navigation issue too much.
Calculating a course to steer is so you can make good your planned navigational track.
Putting a line on the chart as a guide and then using EP to see your position relative to that is a completely different thing.
Both are good as long as you know which you are doing.

A good tip on arrival from previous posters to arrive with tidal stream in your favour. Also if making land fall on a coastline with poor nav features it may be a good idea to purposely aim to east/ west etc of your chosen arrival. Then on making landfall at least you know which direction your intended destination is.
Click to expand...

No not just a sailing thing. Sailor being usualy slow care more about the effect of current on thier progress. by not fighting it they dont loose as much ground.
in open water with no hazards to be concerned with an S shaped is perfectly aceptable. through in a hazard you might want a change of plan.
on a power boat you can stick to the line if you want. it will impact your speed made good over the ground but you wont notice as much.
 
If anything, it's more of a motorboat thing, because you can plan your speed and won't be tacking or thinking about windshifts etc.
Crossing the channel under sail, I would very rarely be sticking to a CTS purely based on a planned boat speed and tides.
But then I probably wouldn't plan to go to Cherbourg....
 
FairweatherDave said:
Do I draw an estimated course, ie an S shaped plot and watch how far off I deviate
Click to expand...

I could be wrong as I've not done a theory course, but I don't believe this is taught by the RYA. However, it seems obvious to me and is what I've always done. Since I've worked out the tidal offsets for each hour anyway, it's simple to plot them on the chart as a series of diagonal crosses (to distinguish from the dot-in-a-circle showing a fix). I then lightly sketch a curve passing through those crosses, as my expected track.

During the passage I plot a fix each hour, and all being well I should see them approximately follow the sketched curve. I certainly don't try to follow that track exactly - the prediction part of the process is not nearly accurate enough for that - but if I see my series of fixes marching steadily away from the line then that's a warning that I might have made a mistake somewhere. How firmly I react to that depends on how far through the passage we are - unless it's grossly wrong I wouldn't expect to make any course change in at least the first half, waiting to see how things develop.

For the last couple of hours I ignore the plan and just point the plotter's predicted track at the harbour entrance - adjusted a little to one side or the other based on whether the tide will be strengthening or weakening. I don't formally recalculate a course at this point.

It's fair to say that with the present boat speed and generally leaving via the Needles, I could probably just point the boat due south for nine hours or so and then aim the predicted track at the harbour entrance when I see it, and not bother with any of this chart stuff. But what else am I going to do to occupy myself under way? :)

Pete
 
Tranona said:
Not confusing it at all. Suspect you need to do a basic course in navigation in tidal waters to understand what an S curve COG is. If you did a cross channel (and therefore cross tide) passage even under motor your track would not follow a straight line but would be influenced by the tide. Not a big deal if you are cruising at 20 knots as you only have 3 hours or so of tidal influence on a 60 odd mile passage, However in a sailing boat at 5 knots your passage time is over 12 hours or a full tidal cycle so you will be pushed one way and then the other so your track will be S shaped over the ground. As the tide is stronger on one side of the channel than the other you need to work out (as the OP has done) the net effect of the tide over the duration of the passage so that you can steer a course that takes into account the effect of the tide.

Nothing clever or magic about it, just a bit of work to work out the tidal effect for each hour of the planned passage, plotting regular positions to check progress and making any adjustment when you get closer to your destination to ensure you arrive upwind and tide. As you see from the various posts this method is just about universal.
Click to expand...

Rubbish.
You either have a navigation track which you want to follow make necessary adjustments to keep on that track or not. Letting the elements dictate where you go is not following a planned track it is just plotting the course you made good over ground. That is why you prescribe an S shaped course.
 
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