NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brad Morris
Date: 2015 Jul 11, 18:16 -0400
Greg
I agree that a standard slide rule would be problematic. Too many steps, too many intermediate values. Ability for an error slip in. All that writing and fiddling makes the solution only feasible, not really practical.
Not so much for a Bygrave. They were designed to work in an airplane cockpit, while also flying the plane. Some might call that 'idiot proof'...
I believe with practice, Mr LaPook has asserted 90 second solution times. You are probably one of the most experienced Hav-Doniol practitioners. How long does that reduction /solution take you ?
The Bygrave is a single purpose slide rule, unlike the Fuller, Otis cylindrical rules or most other linear slide rules, all of which are general purpose. You can solve many problems, including sight reductions, in the general purpose group. The Bygrave solves only the sight reduction problem, and (at least to my knowledge) no others. That's why the Bygrave is fast and accurate, its an ideal reduction to practice. The tables, so common to all sight reductions, are transformed into logorithmic scales wrapped around the two cylinders.
I agree that the general purpose slide rule could take quite a bit of time and would be prone to error. The standard linear 10" slide rule *resolution* is barely adequate. It is to these points, that ranking Hav-Doniol over a linear slide rule becomes obvious. Even the Fuller and Otis cylindrical rules which do have sufficiently resolution, are still subject to the number of steps and intermediate results. These too must yield to Hav-Doniol.
When the special purpose Bygrave is presented, we may have a different conclusion. Speed and accuracy. Idiot proof. Calculation error of 1-2'.
If cost is included, an original MHR-1 is prohibitive. Bygrave reproductions, made by many here, are also more expensive than Hav-Doniol. It is only the Flat Bygrave which can compete with Hav-Doniol for cost. Its simply two printed pieces of mylar.
There are many solutions and methods. The initial comparison between the Bygrave and Hav-Doniol drew what I still feel was an erroneous conclusion. I'm only defending the Bygrave, and not denigrating Hav-Doniol one bit!
Brad
Brad,
I can't speak for a MHR-1 only for a 10" slide rule. There are problems reliably working the rule when going to weather on a small craft. It took me over 15 minutes to complete and then the result was untrustworthy. The 5 place haversine table takes 5 minutes with a confident result. Time extracting LHA, declination, and for plotting are not included in reduction times.
Greg Rudzinski
From: Brad Morris
Date: 2015 Jul 11, 14:08 -0400Hanno
You may wish to examine Mr. LaPook's version of the Flat Bygrave. The mechanical objections to the cylindrical Bygrave you raise are obviated.
If there is a choice between a series of hand and paper calculations or some manipulation on a Bygrave (of either cylindrical or flat type), hands down the Bygrave wins, IMHO. Its far superior to a series of computations performed by hand, as arithmetic errors are all but eliminated.
The Bygrave is accurate and fast. 1'-2' accuracy in less than 2 minutes of time? Combine with low chance of arithmetic error? No contest.
I've not seen any disclosure or publication of the time it takes to perform Hav-Doniol. Perhaps the more experienced practitioners would divulge the elapsed time??
Of course, I am biased. I have an MHR-1. That's superior to the Flat Bygrave as the angle between the scales is automatically maintained, just as in a Fuller or Otis cylindrical rule. The MHR-1 also has a superior locking mechanism to a cylindrical Bygrave. Beautiful instrument but an expensive device. (The expense has driven the reproduction effort and indeed Gary's inventiveness).
This isn't a knock on the Hav-Doniol reduction method. In a recent note, you compared Hav-Doniol to the Bygrave, and came to what I feel is an erroneous conclusion. I herein question that conclusion.
Brad
