NavList:

So I'm out there in 50 foot waves with a mile between peaks.  I take my shot when my boat is at the top of a wave.  This is easy to tell because I can actually see a horizon.  The horizon I see is 8 miles away.  It is always the top of a wave because I can't see the bottom eight miles away.  Why?  There is a crest 7 and 1/2 miles away blocking my view.

 

So the questioned begged is this.  Just how much difference does a horizon 1/2 mile short of true for my height of eye actually make on an observation?

 

Tis my argument that it isn't enough to even consider in practical navigation.  I don't even think you can measure it that far away..

 

 

-----Original Message-----
From: Frank Reed
Sent: Jul 22, 2004 9:37 PM
To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM
Subject: Re: Level of observation accuracy in medium seas

"Did a noon sun shoot within seconds of local noon with 0 magnification sight
tube."

Just curious, did you do anything to verify your calculation that it was local noon? Did you check the altitude before and after to see that it was lower?

Generally, the limiting factor for accuracy is the horizon itself. It takes practice when there are significant waves getting used to picking off altitudes at the moment when you're seeing something approximating a true horizon. Beyond that refraction can shift the horizon up and down in ways that "dip" tables only partially correct. You could count +/-1.5 minutes as very good.

Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois

Dave Weilacher
.US Coast Guard licensed captain
.    #889968
.ASA instructor evaluator and celestial
.    navigation instructor #990800
.IBM AS400 RPG contract programmer