NavList:

In France both in the Military Navy and Civilian Merchant Navy (most of the Merchant Navy Instructors come from the Military) , such problem has long been known as Douwes's problem. To the best of my memories, M. Douwe was a Dutch Navigator of the XIX (?) th century who reportedly had already spent a lot of thoughts about tackling this subject. I do not think he did find the exact solution.

My response:
Thanks Antoine, this is the first time I heard about Douwes. I found a couple of relevant links:

http://books.google.com/books?id=i4SJwNrYuAUC&pg=PA326&lpg=PA326&dq=Douwes's+problem&source=bl&ots=K0Ia6E1kKR&sig=Lc9cf62sEBlCRo4zb897EjYM_Y8&hl=en&ei=wa68SpqnAo3UsgOJ_9HcBQ&sa=X&oi=book_result&ct=result&resnum=5#v=onepage&q=&f=false

http://books.google.com/books?id=UwtDAAAAIAAJ&pg=PA293&lpg=PA293&dq=Douwes+problem&source=bl&ots=4lT3lq3g52&sig=f4pUUZcyLP6e0sxz7LXYH40CA4U&hl=en&ei=2K68So_PH4aQsgO2-OzcBQ&sa=X&oi=book_result&ct=result&resnum=10#v=onepage&q=Douwes%20problem&f=false



Antoine continues:
By 1980 I had devised on my own 3 independent methods of dealing with this, and I did have to wait until then to successfully run them on my (third type of) calculator. One of these methods had I already "invented" some 6 or 7 years earlier when at the French Naval Academy. I had painstakingly but eventually and successfully run only one example then in early 1974 but it had taken me over 10 hours of "manual" computation. I even made a (quite proud) presentation about my method and results to my fellows and instructors who found it ... "interesting indeed, but maybe (or "hopefully" would say the nicest ones in the audience) of some practical interest the future " .. Why such unexpected reaction and feelings ? Simply because WE DID NOT HAVE ANY PRACTICAL COMPUTATIONAL POWER AT HAND THEN !

My response:
Such tedium can be bypassed to some degree if the problem can be reduced to some standardized form.  Then its solutions can be calculated once and tabulated for practical use on a sufficiently fine grid.  So I suppose nobody has printed any "Douwes sight-reduction tables."


Peter Hakel