What an interesting theoretical discussion, guys. Well done.
But, as far as I can see, in the real world, these nits have been over picked. In order for the "steer a constant course" method to work, one must have consistent wind speed and direction and to have tidal and current
info that is completely correct as well.
These two conditions don't often occur in any part of the world that I have yet sailed. My experience does not include "The Channel", and I do understand that because of the strong tidal currents and heavy traffic it has been well studied and charted, but I don't believe that the tidal atlas considers the effects of wind driven currents, atmospheric conditions and all of the other minor things that add up to the actual flow on any given day/time. And in most other parts
of the world, there is no tidal current
data available at all.
And as to the wind (which greatly affects one's boatspeed and perhaps course), it seems to vary a lot when I'm sailing. One can use various means to predict what it will do over the course of a voyage, but IME none of these are accurate enough to make the "constant heading" method work over a whole voyage, or I suspect, even a channel crossing.
So, while the theoretical advantage of that method of navigation
may be real, in practice frequent corrections must be made to reflect actual conditions, and these in turn make rhumb line sailing look pretty practical.
On ocean passages I reckon one is doing well just to avoid areas of known adverse currents, and even this is more difficult than it appears. Those nice broad arrows shown on the pilot charts
are fictitious -- in actuality, the currents are made up of lots of eddies and swirls that are only averaged out on the charts
. The advent of GPS
has for the first time made observation of these small scale phenomena possible. We have experienced large variations in speed and set of currents in mid ocean, events
that would not have been measurable by traditional navigational methods, and which would destroy the usefulness of the constant heading course.
At any rate, what Ann and I have done for our passages is to lay out a course that avoids (on paper) the worst adverse currents, avoids seamounts when possible, avoids reefs
and such impediments by reasonable margins and eventually arrives at our destination
. Then we set out in the best weather
conditions we can find and then sail in whatever conditions Neptune throws at us, attempting to stay near enough to our proposed track to avoid the hard bits. It isn't as elegant as the preplanned constant heading, but it has gotten us where we wanted to go in reasonable time frames for a long time now, and I suspect that most oceanic voyagers do something similar.