Associated Topics || Dr. Math Home || Search Dr. Math

### Military and Nautical Time

```
Date: 06/26/2000 at 12:19:28
From: Angela
Subject: Nautical to Standard

What is the formula to convert nautical hours to standard hours?
```

```
Date: 06/26/2000 at 13:26:22
From: Doctor Rick
Subject: Re: Nautical to Standard

Hi, Angela.

When I saw your subject line, I thought you must want to convert
nautical MILES to statute miles, the kind we use on land. (There are
1.1508 statute miles in 1 nautical mile.)

What is a nautical HOUR? I never heard of it. As far as I know, an
hour is an hour.

Perhaps you're referring to military time. Military time uses a
24-hour cycle, but the hours are the same length as "standard" hours.
The military time 1600, for example, is 4:00 PM (4 hours after 12
noon, or 1200.) People call it "sixteen hundred," but it's really 16
hours and 0 minutes after midnight. The minute after 1659 is 1700,
because 60 minutes make an hour just as in "standard" time.

This chart converts military time to standard time.

Military (24-hour)    Standard (12-hour)
------------------    ------------------
100                   1:00 am
200                   2:00 am
300                   3:00 am
400                   4:00 am
500                   5:00 am
600                   6:00 am
700                   7:00 am
800                   8:00 am
900                   9:00 am
1000                  10:00 am
1100                  11:00 am
1200                  12:00 noon
1300                   1:00 pm
1400                   2:00 pm
1500                   3:00 pm
1600                   4:00 pm
1700                   5:00 pm
1800                   6:00 pm
1900                   7:00 pm
2000                   8:00 pm
2100                   9:00 pm
2200                  10:00 pm
2300                  11:00 pm
2400                  12:00 midnight

- Doctor Rick, The Math Forum
http://mathforum.org/dr.math/
```

```
Date: 04/20/2005 at 15:23:31
From: Elliott
Subject: Military (Nautical) Time Solution

Browsing your site, I came across the question on Nautical Time.
There actually is something that could be called nautical time.  It
is time measured in bells.  The time is announced by ringing of bells.
The conversion table is:

BELLS    TIME
8        0000
1        0030
2        0100
3        0130
4        0200
5        0230
6        0300
7        0330
8        0400
1        0430
2        0500
3        0530
4        0600
5        0630
6        0700
7        0730
8        0800
1        0830
2        0900
3        0930
4        1000
5        1030
6        1100
7        1130
8        1200
1        1230
2        1300
3        1330
4        1400
5        1430
6        1500
7        1530
8        1600
1        1630
2        1700
3        1730
4        1800
5        1830
6        1900
7        1930
8        2000
1        2030
2        2100
3        2130
4        2200
5        2230
6        2300
7        2330
8        2400

I suppose that there is an assumption that a person hearing the bells
would have some notion of what 1/6th of the day it is, and that it is
therefore "intuitively obvious" what time it is.

I know, I'm 67 years old and I should probably not be reading Middle
School questions!  However, they are interesting and I am getting some
insights that I never had while I was in school myself.
```

```
Date: 04/23/2005 at 17:25:14
From: Doctor Rick
Subject: Re: Military (Nautical) Time Solution

Hi, Elliott.

I am familiar with the meaning of the "bells" because my father was
in the Marine Corps and he had a clock that chimed the bells. As I
understand it, the bells are a subdivision of the "watches", the four-
hour periods into which the day was (is?) divided for shipboard watch
duty -- which segment of the crew is on duty at any given time. If
you know what watch you are on when you hear the bells, there will be
no ambiguity about what hour it is.

I get most of my knowledge of watches from Patrick O'Brian historical
novels, which is why I said "was" above. But prompted by your
comments, I found an interesting reference on this topic:

Nautical Know How: Watch Schedules and Ship's Bells

I quote:

"As early as the 15th Century, a bell was used to sound the time
onboard a ship. ... The bell was rung every half hour of the 4 hour
watch. A 24 hour day was divided into six 4 hour watches, except the
dog watch (16:00 - 20:00 hours) which could be divided into two 2
hour watches to allow for the taking of the evening meal.

Middle Watch      Midnight to 4 AM (0000 - 0400)
Morning Watch     4 AM to 8 AM     (0400 - 0800)
Forenoon Watch    8 AM to noon     (0800 - 1200)
Afternoon Watch   Noon to 4 PM     (1200 - 1600)
First Dog Watch   4 PM to 6 PM     (1600 - 1800)
Second Dog Watch  6 PM to 8 PM     (1800 - 2000)
First Watch       8 PM to Midnight (2000 - 0000)

"The bells were struck for every half-hour of each watch, with a
maximum of eight bells. For instance, during the Middle Watch you
would hear the the following:

00:30 1 bell
01:00 2 bells
01:30 2 bells, pause, 1 bell
02:00 2 bells, pause, 2 bells
02:30 2 bells, pause, 2 bells, pause, 1 bell
03:00 2 bells, pause, 2 bells, pause, 2 bells
03:30 2 bells, pause, 2 bells, pause, 2 bells, pause, 1 bell
04:00 2 bells, pause, 2 bells, pause, 2 bells, pause, 2 bells

"At eight bells your watch was over! All other 4 hour watches
followed this same procedure except the Dog Watches.

"At the end of the First Dog Watch, only four bells were struck, and
the Second Dog Watch bells were struck like this: 6:30 PM, one bell;
7 PM two bells; 7:30 PM, three bells; and at 8 PM, eight bells.

"Since 1915, all U.S. Merchant vessels over 100 gross tons have, by
law, divided the crew into three watches, working four hours on and
eight hours off, and turning the dog watches into one evening watch."

We will never know what Angela had in mind, but I don't think bells
(or watches) relate to her expression "nautical hours". Information
on this subject is worth having, in any case, so thank you for
mentioning it.

- Doctor Rick, The Math Forum
http://mathforum.org/dr.math/

```
Associated Topics:
Elementary Calendars/Dates/Time
Middle School Calendars/Dates/Time

Search the Dr. Math Library:

 Find items containing (put spaces between keywords):   Click only once for faster results: [ Choose "whole words" when searching for a word like age.] all keywords, in any order at least one, that exact phrase parts of words whole words

Submit your own question to Dr. Math
Math Forum Home || Math Library || Quick Reference || Math Forum Search