# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Message:αβγ
Message:abc
 Add Images & Files Posting Code: Name: Email:
Re: Height of Eye on a ship.
From: Jeremy C
Date: 2022 Dec 2, 08:26 -0800

We do use plumb bombs from the main deck for draft surveys.  They are very difficult to get accurate.  I can't imagine trying it from the bridge deck.  Between wind blowing the string/sound tape around, and the waves affecting the height as well, it's a crap shoot.  We actually tend to put people over the side in Jacobs ladders and other devices to read the draft marks as they are far more accurate to determine.

Next week I'll be on my ship and I'll try the laser range finder in my binoculars and see how that compares to my calculated values.  Sometimes the laser doesn't read too well off the water surface.

My Dip exercise with cadets is a didactic.  I am attempting to teach them how to think critically and pay attention to details.  Dip calculation is an easy and harmless way to convey this lesson.  The REAL use of this methodology is calculating air draft.  There are things at sea when being sloppy can lead to accidents; like hitting bridge spans because you "guestimated" too many factors. See this story.  I have had to bring two different ships under that very same bridge with about 3 ft of under-keel clearance, and less than 4 feet under the bridge span.  You can bet my math as as painstakingly detailed as anything I run a cadet through.

Jeremy

Browse Files

Drop Files

### Join NavList

 Name: (please, no nicknames or handles) Email:
 Do you want to receive all group messages by email? Yes No
You can also join by posting. Your first on-topic post automatically makes you a member.

### Posting Code

Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
 Email:

### Email Settings

 Posting Code:

### Custom Index

 Subject: Author: Start date: (yyyymm dd) End date: (yyyymm dd)