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Bruce,

It was officially called a "Mark I Ball Recording Sextant". I like to call
it the "Kerplunk" sextant.

It was an experiment -- one of many in a quest to find the perfect
artificial horizon sextant -- that did not work out in practice as it did on
paper. In the end, the bubble sextant was the most practical and dominated
the field.

I own a Kerplunk sextant that is in mint condition. Mine is dated 1944. US
Navy Bureau of Ships

The sextant works essentially like this:

The operator allows the pendulous alidade to swing freely until the observed
body is approximately in the centre of the view, upon which he locks the
alidade by pulling a trigger mechanism. He then fine tunes the recording by
adjusting a fine adjust knob at the same time, squeezing another trigger
mechanism which allows lead shot to drop, one shot at a time, onto piece of
carbon paper which leaves an impression dot on a graph plate. The observer
then examines the graph plate and tries to average out the dots to come up
with a number. I am likely not doing a very good job of describing the
process but if you want, I can send you a copy of the instructions.

Short answer: the Ball Drop Sextant did not live up to it's promise and in
fact proved to be too cumbersome and too inaccurate.

I have tried bubble sextants and bubble attachments at sea many many times,
and have found that bubble horizon observations at sea these yield dubious
results; even when the sea is flat-arsed calm. Of course I have all of the
data from my past efforts. It's fun to try, but in terms of usefulness, I
would question the value of one's efforts unless you simply had nothing else
to go on.  Just for your interest, some of the pioneer aviators in the
Canadian Arctic (we are talking the 1920's and 1930's) used marine sextants
for navigating through the trackless barrenlands. In the absence of a decent
DR position, they would land on a lake, set up an artificial horizon and
take sun shots. I have a photo of this operation.

my two bits' worth.

Robert



----- Original Message -----
From: "bruce hamilton" 
To: 
Sent: Sunday, November 09, 2008 1:43 AM
Subject: [NavList 6466] Re: sextant without paper charts


>
> Four who actually know how to use the sextant. On coastal merchant ships
> it went like this :-)
>
> The Old man knew everything about the sextant, but didn't tell you.
> The First Mate used to know, but was too busy running the ship
> The Second Mate knew it for his exams, but forgot the details.
> The Third Mate was going to know when after he wrote his exams.
> The Navigation Cadet wanted to know, but could not find anyone to teach
> him.
>
> Question: I spent a lot of time sailing the foggy waters around
> Newfoundland, and we would often have a sunny day above, but the horizon
> was obscured by fog. Does anyone on the list own one of those sextants
> that drop a bit of shot to calculate the horizon? I believe the US Navy
> had them.Were they any good?
>
> If the sextant had continued to evolve, I think a gyroscopic base might
> have been a good route. I saw one somewhere.Does anyone know about those?
>
> Did inertial navigation ever make it to the Merchant Navy bridge or is
> it still military only?
>
>
>
>
> frankreed@HistoricalAtlas.net wrote:
>> And three days after I wrote about this on NavList, I see that one Tim
>> Queeney blogged about it on oceannavigator.com:
>> "The U.S. Navy is well known to be secretive about its nuclear
>> submarines.
>> [...] But as ON contributor Greg Rudzinski points out, there is one piece
>> of
>> gear that sub officer's will discuss: the fact that the boat carries a
>> sextant. Check out this article on the new U.S.S. New Hampshire from the
>> Nashua, New Hampshire Telegraph. One of the sub's officers actually
>> admits
>> there are only four members of the crew who know how to use this rare
>> navigational device. "
>>
>> A hot topic. :-)
>>
>>
>>
>> frankreed@HistoricalAtlas.net writes:
>>
>>
>>> Here's an article about a tour of the new Virginia class submarine "New
>>> Hampshire" which is almost ready to joing the fleet (the URL below
>>> should be
>>> all on one line; just in case your web browser or email client doesn't
>>> render it that way):
>>> http://www.nashuatelegraph.com/apps/pbcs.dll/article?AID=/20081021/NEWS01/310219927/-1/news01
>>>
>>> Right at the top, the article notes that the submarine carries a
>>> sextant,
>>> just in case. Later in the article, it's explained that they carry no
>>> paper
>>> charts.
>>>
>>>  -FER
>>>
>>
>>
>>
>> >
>>
>>
>
>
> >
>



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