# 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: Bubble Sextant as Dip Meter
From: David Pike
Date: 2015 Oct 23, 16:44 -0700

I was reading HO551, Manual of Ice Seamanship.

After a discussion of abnormal refraction and the care a navigator should take in regards to it, the following interesting statement is made

"If the motion of the ship permits use of a bubble sextant, it can quickly be determined whether the apparent horizon is appreciably displaced"

The manual gives no further information.
Am I to infer that a bubble sextant can be used as a dip meter.  Or is it merely a gross check, as in 'the horizon is far from normal'.

Has anyone tried this?  Can a bubble sextant be used as a dip meter?

I think it would depend upon the bubble sextant used and your definition of appreciable.  I’ve never used a marine sextant with a bubble attachment, so I can’t comment on that.  It is conceivably possible with an RAF MkIX or an RAF Periscopic Mk2.  The mirrors are set in ten degree steps and the counter reading is added to the number of tens.  Both start from a D (-10°) position.  I’ve not looked at my American sextants recently.  However, you’re unlikely to get closer than one minute accuracy and the slightest acceleration will reduce the accuracy considerably.  Three minutes is typical.  If three minutes accuracy is sufficient for your purpose, then you could use such a sextant as a dip meter.  I’ve never worked using the D position, but I believe it was incorporated, because at altitude it’s possible to see bodies below the surface horizon, Nories says 1° 38’ below from 10,000ft.  It was also quite useful over the sea for calculating a range from a distant coastal feature.  I vaguely remember there was a formula for this, but I’m afraid I’ve forgotten it long ago.  DaveP

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)