# 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: Need dip-throw a rock?
From: Tom Sult
Date: 2011 Jun 22, 21:10 -0500

```For a relatively higher bridge would you expect a larger or a smaller
error.  I am thinking that the time to push the button is constituent
and the total time is greater resulting in a smaller error.  If you
let go a few of those steel balls into the ocean from a hight of say
30 meter what might one expect?
Thomas A. Sult, MD
3rd Opinion
1415 First First St. South #5
Willmar, MN 56201
320 235 2101 Office
www.3rdOpinion.us
tsult@mac.com

On Jun 22, 2011, at 5:58 PM, Bill Morris wrote:

> I thought I would discover how well the rock-throwing method might
> work for me in practice. To avoid discussion about the behaviour of
> feathers and the shape of rocks, I used petanque balls. These are
> polished steel balls of 72 mm diameter and weighing 500 grammes,
> used in the game of petanque (q.v.).
>
> I threw them horizontally from the bridge of our ship
> "Baradozic" ("Little Paradise" in the Breton language - my wife is
> from Brittany)and used a stop watch reading to 0.01 second to time
> their fall onto level ground a measured 5.8 metres below.
>
> The mean time of 25 throws was 1.29 seconds, with a standard
> deviation of 0.087 seconds, so that we could expect 95 percent of
> the times to fall in the range 0.95 to 1.63, as indeed they
> comfortably did (1.04 to 1.47).
>
> Taking the local acceleration due to gravity to be 9.805 metres/s/s
> gives a height of 8.16, an error of nearly 30 percent. This would
> give a dip error of 0.8 arcmin.
>
> The error is in the right direction. If one assumes a timing error
> of 0.1 seconds (and you don't have to be old and decrepit to have
> such an error when operating a stop watch), we get a much closer 6.9
> metres.
>
>
> Bill Morris
> Pukenui
> New Zealand
> ----------------------------------------------------------------
> NavList message boards and member settings: www.fer3.com/NavList
> Members may optionally receive posts by email.
> To cancel email delivery, send a message to NoMail[at]fer3.com
> ----------------------------------------------------------------
>
> File:

```
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)