Autopilots and Tides, headings and tracks

[Giblets]

With an all-singing all-dancing George, you'd also have to have a word in his ear about leeway.

And then interface him with the wind instruments so that mid-course corrections are automatically made if the wind strengthens, drops, backs or veers together with the AIS to avoid any shipping.

Strikes me as being a very boring way to cross the Channel - might as well get a ferry!

 

[bbg]

Software like MaxSea will certainly calculate the route for you (including taking into account wind shifts), but not sure how you then get the AP to follow the optimal route.

 

[johnalison]

My old Navstar Decca could be given a tidal offset and then calculate the course to steer, which was often surprising effective. For a cross-Channel trip is not exactly difficult to set the pilot to a compass course, which only need be approximately correct and then steer to a waypoint for the last couple of hours, assuming the tide will not be changing.

 

[prv]

Given that the tide strength & direction on charts, whether paper or electronic, is not absolute it must be subject to error.

What do you mean by "not absolute"?

The opposite of absolute is relative; what is it relative to?

The Coastguard have access to drift prediction software (for predicting the likely location of a man overboard, a liferaft, a disabled vessel, etc) which is reputed to be quite accurate. The same data ought to be more than good enough for predicting a course to steer, if it were available to the makers of nav software.

Pete

 

[laika]

Software like MaxSea will certainly calculate the route for you (including taking into account wind shifts), but not sure how you then get the AP to follow the optimal route.

maxsea seems to list autopilot control as a feature (though it's a bit out of my price range):
http://www.maxsea.com/products/software/maxsea_timezero_products_range


IIRC OpenCPN sets AP heading using the NMEA-0183 APB sentence

 

[RobbieW]

What do you mean by "not absolute"?

The opposite of absolute is relative; what is it relative to?

The Coastguard have access to drift prediction software (for predicting the likely location of a man overboard, a liferaft, a disabled vessel, etc) which is reputed to be quite accurate. The same data ought to be more than good enough for predicting a course to steer, if it were available to the makers of nav software.

Pete

I was trying to find a phrase that encapsulated 'subject to error' or something similar in that each day is different. I have no actual knowledge of the drift prediction software used by the CG etc, my thought is that it would be similar to the models used by Met Offices to predict weather in that it would require various inputs reflecting actual fluid conditions on the day - what navigation software seems to do is generalise and that is not going to give values that are always true. Though I'm sure your point is correct in that if those variables were publicly available and built into nav software it would do an equally good job (with the use of a little processing power of course).