# 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: Fatal interaction betweeu yacht and ferry.
From: Gary LaPook
Date: 2007 May 08, 17:52 -0700

```Gary writes:

Absolutely, that comes from the standard radar equation. To double
the detection range you need to increase the power of the echo by a
factor of 16, holding everything else constant, and this can be
accomplished by increasing the power of the transmitter  or increasing
the size of the radar cross section.  Since you can't control the
output power of the other guy's radar the only thing you can do is
increase the size of the radar reflector. (Or you can use an active
transponder.) So you are right, after you do the math the detection
range increases linearly with the size of the radar reflector, double
the size and you can be detected at double the range, which is not a

But what is really critical is not the distance that your boat can be
detected but whether it can be detected at all. With sea clutter,
unless your boat produces an echo above that of the existing sea
clutter you will not be detected at all. An echo that is 16 times as
strong because you are using a reflector twice as big has a very good
chance of lifting you out of the clutter so you can be detected. Even
just doubling the power by using a reflector 19% bigger may make all
the difference in being detected or run down.

On May 8, 4:42 pm, Paul Hirose  wrote:
> glap...@PACBELL.NET wrote:
>
> > I don't think most sailors realize how much size matters when it comes
> > to radar reflectors and may be tempted to "just get the slightly
> > smaller one." Since the echo varies with the fourth power of the size
> > a small change in size  will make a large increase in echo strength.
> > Changing the size by 19% changes the echo by a factor of two since
> > 1.19 is the fourth root of two.
>
> On the other hand, isn't it true that detection range varies with the
> fourth root of the radar cross section? If so, the detection range of
> the reflector alone would be proportional to the linear size of the
> reflector.
>
> --
> I block messages that contain attachments or HTML.

--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To unsubscribe, send email to NavList-unsubscribe@fer3.com
-~----------~----~----~----~------~----~------~--~---

```
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)