NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Fatal interaction betweeu yacht and ferry.
From: Gary LaPook
Date: 2007 May 08, 17:52 -0700
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 bad thing.. 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 Hirosewrote: > 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 , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---