NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2015 Jan 22, 12:43 -0800
It is necessary to note that originally the intercept, or Marc St. Hilliare, method was employed using a DR position, however, in the search for more speedy solutions and the advent of the various short tabular methods, utilizing whole numbers for Latitude and LHA, it became necessary to manipulate the vessel's actual DR position, both in Latitude and Longitude to accomodate this end - so the position "assumed" to achieve this end was named the Assumed Position, or AP. I have never had any problem understanding this as the basis of many short tabualr methods.
A review of the instructions at least to HO 208 and HO 214 should clarify this use of tha AP.
Henry
Well said Henry, that’s what I thought, although in the RAF it was more a case of ‘This is how you are to do it’. We picked our assumed position to give us whole degrees of Latitude and LHA to enter HO208/214 (AP3270 in the UK) with. I must say, I did as I was told for 15 years without giving it another thought. Just looking at one of our pre-computation proforma, I see that having selected our assumed position, we moved it a bit (on the chart not in the tables) to allow for Corioli’s aceleration, rhumb line steering, change of variation, and precession and nutation. Don’t ask me to explain RLS and CoV, because I can’t remember. I think it depended upon which heading reference you had selected whether you applied them or not. I’ll have to check on that. Dave
