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  1. #41
    Join Date
    Nov 2009
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    Home UK Midlands / Boat Croatia
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    14,662

    Default Re: Course to steer for crossing the channel

    Quote Originally Posted by East Cardinal View Post
    Rubbish.
    Have you ever actually seen an East Cardinal?

    Richard

  2. #42
    Join Date
    Oct 2012
    Posts
    2,788

    Default Re: Course to steer for crossing the channel

    Quote Originally Posted by East Cardinal View Post
    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.
    I understand your point of view and in some circumstance you are right. Depends on the situation. Remove all other considerations leaving just a course to steer to get to a destination and a full cycle of tide and the resulting current being on the beam.
    Just by the basic laws of mathematics particularly vectors. The S is more efficient.
    The significance depends on the relationship of speed of the vessel compared to the rate of drift.

    Just a side consideration for a relatively slow vessel crossing a TSS. A constant course through the water is generally preferred over a constant course over the ground.

  3. #43
    Join Date
    Sep 2016
    Posts
    106

    Default Re: Course to steer for crossing the channel

    Don't forget to check that your predicted S-shaped course doesn't put you in a dangerous position.

    At night I find it much easier to steer while reading the cockpit display (COG) than the compass (Heading), and so what I have done in the past is enter a series of 'virtual' waypoints along the calculated ground track. For each ~2 hour 'leg' you just have to aim for the next waypoint (have CtW on the display as well), and every so often check that your heading is correct.

    This makes the helmsman's job really easy, but might well be overkill for a channel crossing.

    Trust your calculations, and resist the temptation to deviate towards the straight line. It is disconcerting being swept at 45 degrees from the natural path.

  4. #44
    Join Date
    Nov 2009
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    Home UK Midlands / Boat Croatia
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    14,662

    Default Re: Course to steer for crossing the channel

    Quote Originally Posted by Uricanejack View Post
    Just a side consideration for a relatively slow vessel crossing a TSS. A constant course through the water is generally preferred over a constant course over the ground.
    "Generally preferred"? That seems a strange choice of words bearing in mind the ColRegs rule.

    Richard

  5. #45
    Join Date
    Oct 2012
    Posts
    2,788

    Default Re: Course to steer for crossing the channel

    Quote Originally Posted by RichardS View Post
    "Generally preferred"? That seems a strange choice of words bearing in mind the ColRegs rule.

    Richard
    It's a bit wishy washy but I prefer not to use absolutes. JIk there is that odd situation.

  6. #46
    Join Date
    Jun 2007
    Location
    On board
    Posts
    2,539

    Default Re: Course to steer for crossing the channel

    Quote Originally Posted by FairweatherDave View Post
    Let's rephrase that. If I resubscribed to Navionics it can calculate a course to steer for me based on my location, time of day and destination?
    Assuming you meant 'can it' rather than 'it can' then no, as far as I'm aware - at least not one that will take tide/current into account. I still find it easier to do as CS suggests and go old school for tidal CTS estimation, still using ReevesFowkes too. The only addition I'd make to other comments is that I'll check my CTS at slack, usually about halfway when using the Needles channel. I use an hour by hour tidal proforma annotated with tide angle and strength so comparing my actual timings and position with the predictions is easy enough and adjust if necessary. Dont forget that tide is (quite a lot) stronger around the end of the Cherbourg peninsula and has some interesting eddies close in to the west.
    If you're not confused, you're probably misinformed

  7. #47
    Join Date
    Jul 2002
    Location
    Farnham, Surrey
    Posts
    19,782

    Default Re: Course to steer for crossing the channel

    Quote Originally Posted by TLouth7 View Post
    Don't forget to check that your predicted S-shaped course doesn't put you in a dangerous position.

    At night I find it much easier to steer while reading the cockpit display (COG) than the compass (Heading), and so what I have done in the past is enter a series of 'virtual' waypoints along the calculated ground track. For each ~2 hour 'leg' you just have to aim for the next waypoint (have CtW on the display as well), and every so often check that your heading is correct.

    This makes the helmsman's job really easy, but might well be overkill for a channel crossing.

    Trust your calculations, and resist the temptation to deviate towards the straight line. It is disconcerting being swept at 45 degrees from the natural path.
    The COG lags behind course alterations, the compass doesn't. I really don';t understand how you find it easier to steer to a COG reading than a compass. I'd be looking at the visibility and lighting of the compass if it was hard to steer to it.

    I rarely hand steer on passage anyway so its easy to glance at the compass now and again and make sure we are still on course.
    Semper aliud

  8. #48
    Join Date
    Oct 2017
    Posts
    65

    Default Re: Course to steer for crossing the channel

    Here's a simulated plot of a 12 hour trip mid-neaps-to-springs at 5 kts with a course of 180 degrees from the Needles
    Note the tides are stronger on the French side.
    ChannelCrossing.gif
    In practice, I check my position about 2 hours out and recalculate a CTS

  9. #49
    Join Date
    Feb 2006
    Location
    Burnham on Crouch
    Posts
    4,257

    Default Re: Course to steer for crossing the channel

    Quote Originally Posted by East Cardinal View Post
    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.
    On a cross Channel passage, if you stick to a straight line over the ground, you are always, effectively making small course adjustments to 'fight' the varying tide.

    Distance through the water will therefore be increased, and passage times longer than necessary.

    It's more efficient, therefore, to do what most on here suggest. ie use a tidal stream atlas (or modern alternative), to plan a constant course to steer that deliberately describes an S-shape over the ground, but a straight line through the water (assuming it is clear of obstruction, of course),

    Passage times and fuel usage will both reduce, though, as Tranona pointed out, the difference will be less noticeable if you can cruise at 20 knots, rather than 5 knots.

    Anyway, it certainly ain't 'rubbish'!
    Last edited by NealB; 14-02-18 at 11:38.

  10. #50
    Join Date
    Feb 2007
    Location
    Essex
    Posts
    18,508

    Default Re: Course to steer for crossing the channel

    Quote Originally Posted by NealB View Post
    On a cross Channel passage, if you stick to a straight line over the ground, you are always, effectively making small course adjustments to 'fight' the varying tide.

    Distance through the water will therefore be increased, and passage times longer than necessary.

    It's more efficient, therefore, to do what most on here suggest. ie use a tidal stream atlas (or modern alternative), to plan a constant course to steer that deliberately describes an S-shape over the ground, but a straight line through the water (assuming it is clear of obstruction, of course),

    Passage times and fuel usage will both reduce, though, as Tranona pointed out, the difference will be less noticeable if you can cruise at 20 knots, rather than 5 knots.

    Anyway, it certainly ain't 'rubbish'!
    The OP originally asked if he should plot the S-curve in advance. In the unlikely event of me being asked to navigate a RN ship, this is something I might well do, but it is far too much hassle for general use, though, as has been said, I would look to see if my XTE, cross-track-error, took me into danger or somewhere I shouldn't be.

    When crossing a shipping lane or TSS I would normally maintain a constant heading, irrespective of the COG.
    Far away is near at hand in images of elsewhere

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