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Joe:

Thanks for your insightful comments.  Some of the comments on this list 
listing all the reasons why new technology (from GPS's to 
auto-compensating compasses) shouldn't work remind me of the old saw 
"according to aeronautical engineers, the bumblebee shouldn't be able to 
fly; not being an aeronautical engineer, the bumblebee keeps flying."

The only comment I'd make here is that the job of a compass in an 
autopilot is significantly different than that of being a 
course-indicting compass.   The job of an autopilot's compass is to keep 
whatever course the helmsman sets into it (typically by steering in the 
correct direction and then punching "set" into the autopilot).  At that 
point it doesn't matter which direction the fluxgate thinks it's 
pointing; it's job is merely to tell the autopilot when it's no longer 
pointing in that direction.   So, for example, it doesn't matter whether 
an autopilot's compass's "lubber line" is aligned with the boat's keel 
or perpendicular to it.


joseph_schultz@rrv.net wrote:
> George, the sweet spot is relative to the capability of the computer to 
create a deviation equation/table which, although you won't see it, may be as 
curvy as your favorite Greek goddess.  Also relevant to the sweet spot is the 
need to be "far enough" away from transient field sources, such as electrical 
cables or transmitting antennas, but this isn't part of the deviation 
question.
>
> Do steel vessels exist in your area, George?  Ferries, commercial fishing 
boats, yachts, etc?  How about taking a trip down reality lane and finding 
them?  I'll bet at least some have autopilots.  And at least some of those 
use a fluxgate or equivalent as direction input.  How are their sensor 
assemblies mounted in the real world?  You'll see, if you choose to look and 
ask, the successful installations are pretty simple, and rarely high on the 
mast as you (and Bowditch-2002) think are needed.
>
> No idea what "warship bristle" means - an armchair term?  Going aloft isn't 
a big deal.  Maintenance gets done and new sailors get initiated.
>
> One author's very short synopsis of the still prevailing point of view, 
regarding aluminum superstructures vs. battle damage in the Falklands War, 
can be found here:
>
> http://www.hazegray.org/faq/smn6.htm
>
> Scroll down to sections F.6 and F.7.  Not mentioned is the maintenance 
headache - gasketing  was used to isolate the very, very special steel from 
normal steel in a mostly futile attempt to prevent bi-metallic corrosion.  On 
my ships you could see holes where the very, very special steel bulkheads met 
the normal steel main deck.  The very, very special steel in the Oliver 
Hazard Perry class frigates was also in the hull.  Back to the topic: 
fluxgates were installed on all-steel Naval vessels, before the ring laser 
gyros were proven and retrofitted, and they worked.
>
> Joe
>
>
>   

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