NavList:

   

Reply

A message from Barrie Hudson, quoted below, was sent, or forwarded (not
sure which) to this list.


>----- Original Message -----
>From: "bhudson" 
>To: "Rodney Myrvaagnes" 
>Sent: Monday, April 22, 2002 4:50 PM
>Subject: Re: Re: Still on LOP's
>
>
>> From a practical point of view that part of the cocked hat that is closest
>> to land is taken as the position. This is for safety. This is a most
>> interesting discussion. With so many chances of error when using P/L's any
>> fix is a best approximation however we strive for accuracy.
>> Barrie


This was the attitude taken by old-school navigators in the erroneous
belief that the true position must always be embraced by the cocked hat.

It interests me what degree of safety Barrie thinks he is achieving when he
takes that part of the cocked hat that is closest to land as his position.

It has, I hope, been generally accepted by most listmembers by now that
there is only a one-in-four chance that the true position will be contained
within the cocked hat at all. If a navigator insists on assuming, against
the evidence, that he must be within the cocked hat, then he will get a
marginal improvement in his safety by presuming that he as at that part of
the triangle which is nearest the danger, rather than at its centre. But he
is being unduly complacent, and there is a strong chance that he may be
significantly nearer still to the danger. The only safe thing to do is to
assess the likely errors involved, in the light of his previous experience,
and allow an appropriate offset. This offset should always be greater, and
might be many times greater, than the dimensions of a particular cocked
hat.

George Huxtable

------------------------------

george@huxtable.u-net.com
George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
Tel. 01865 820222 or (int.) +44 1865 820222.
------------------------------

   

Reply