NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Relative plotting vs Geographical plotting
From: Brian Whatcott
Date: 2002 Jan 11, 7:05 PM
From: Brian Whatcott
Date: 2002 Jan 11, 7:05 PM
At 03:43 PM 1/11/02, you wrote: >George Huxtable [mailto:george@HUXTABLE.U-NET.COM] said: > > > > I don't think Peter Smith's solution can possibly be correct: commonsense > > tells me so. We have two ships travelling in nearly the same direction, >and > > the second ship is slowly overtaking the first. In that case, the speed of > > the overtaking ship must be greater than that of the ship being overtaken. > >Hmmm. I'm not sure from the above who's the "second ship" and who's >the "first ship". The target is ahead of us and to Port (bearing 322d). >The bearing is constant, so we are converging. Since the target is >ahead and the range is decreasing, we must be overtaking the target. > > > ... > > If you add the vectors 12 knots at 150 and 1.45 knots at 142, using trig >or > > drawing, you end up with 13.44 knots at 149.1. > >But that gives the target a greater speed than our own ship, even >though we are overtaking it. > >Moreover, the target is on our Port bow (bearing 322d). For our >courses to converge (constant bearing), the target's course must >be a little to starboard (i.e., numerically GREATER) of ours. Thus, >if we're making 150d, he should be making a little greater then 150d. >If he's making 149.1d, we would be diverging. > >Can you read an Excel spreadsheet? I have both the geographic and >relative vectors problems worked out trigonometrically. I'll send >it to you and see what you think. > > -- Peter Peter, you have already said enough to substantiate your position without support from a product of the evil empire. (ugh!). Brian Brian Whatcott Altus OK Eureka!