Radar

[Rodney]

Ah jeeeze..I was at West Marine today (on a totally innocent, inexpensive errand, honest officer). The next thing I knew I stumbled into a deal on a RayMarine RL70CRC radar/chart display head that I simply could not refuse. In the heat of the moment, I picked up a 2KW 18" radome for it also. In retrospect however, I wonder if I should swap it for the 4KW 24" radome or whether I'll be set with the 2KW.

I worked as a marine electronic tech for years so I should be the one answering this question, but when I was doing it, I worked on "work" boats (fish boast and tugs) and have little experience with sail boats. When this question came up with work boats, I always answered "buy the most you can afford". But such things as power consumption, weight aloft and dome size were almost non-existent as issues.

Any guidance out there? The 4KW is another grand that could be perhaps better spent on..well..what I supposed to buy at West Marine in the first place...

-Tranquility  '87 Hull # 290
San Diego

[rdavison]

Here are my thoughts....

Practical sailor did an LCD radar review in the Nov 1 issue.  Some comments from there and some from my personal experience.

The answer to your question, as you already know, is - it depends.  The 18", 2kw dome is rated good by PS.  The 24", 4 kw dome is rated excellent.  Both were at the top of the list as were the RL70 and SL70 display units so you can't go too far wrong.

Considerations:

How far do you need to see?  The extra power and antenna gain are only useful if you can mount the radar high enough.  Range is 1.14X square root of antenna hight for sea level targets.  From there is depends on how high the target is.  I guess that for sailing offshore from San Diego, you might want to see tall hills of Islands and shore so it may matter to you.  Extra power also helps see targets with lower reflectivity cooeficients.

How much do you care about discriminating one target from another close one?  The horizontal beamwidth of the 24" is 1.2 degrees narrower than the 18".  I think this is more valuable than range.

How much do you care about visual impact and weight aloft?  Getting the antenna higher to get more range also puts weight up high where you don't want it and 24 inches looks pretty big!

One consideration with built in conflicts has to do with safety.  If you mount the antenna high on the mast, you have no safety concerns and good range.  If you mount the 24" antenna on a stern pole you have wasted the extra power since range will be hight limited and you also are putting more RF into your cabin and foredeck areas.  Safety is sometimes an overblown concern since the average output power of the radar is less than 50 watts and the strength falls off rapidly with distance.  Nothing compared to holding a cell phone against the side of your head but worth some consideration if the radar will be on a lot.

Here's what I did:

I chose a Furuno 1622 even though it was one of the lower rated units by PS.  I had a chance to use one in the field and concluded they must have had a bad unit or a bad day since it did all of what they said it wouldn't do.

The reason for choosing it was that I liked the display unit best and the small size and weight of the 15" 2.2kw dome.  I mounted it at the backstay split using a radar-on-the-level swinging mount and wanted it small and light.

I've been extremely pleased with the perfomance of the unit.  The lower power and lesser horizontal beamwidth don't bother me at all.  I cruise in inland salt waters in Washington and BC and usually have the radar set to 4 miles range.  This gives me plenty of time to see freighters and still see local targets.  In a deep fog, I also set it at 1/4 mile to see crab pots and fishing net floats with an occasional look out to 4 miles.  I've never needed longer than 8 miles and can only see high mountain peaks at 16 miles.

Bad rain showers are very visible as are tug and barge combinations, which require extra caution.

Hope that helps - k7voe

Randy Davison  #1268 1993 k7voe

[rdavison]

The radar review was in the Nov 1, 2000 issue - Volume 26, number 21

Randy Davison  #1268 1993 k7voe

[Rodney]

Thanks for the well thought out reply Randy. I'll stick with the 2kw as it appears it will really meet all of my immediate needs...

-Tranquility '87 Hull # 290
San Diego WA7ZIA

[cholder]

I have a Raytheon SL70 with a 2KW antenae and find it perfectly adequate for BC coastal waters.  I mounted the unit on a post embedded in a fibreglass tube glassed  into the starboard quarter on my 1988 C34.  The display is mounted at the wheel in a cranked back pedestal guard made for me to Edson's style by a local fabricator.

[chudave]

Rodney,

I have the RL70 2KW radar in San Diego, and I am very happy with it for what we need it for.  It works great in the fog coming back from Catalina and crossing the shipping lanes at night.  


Dave Chu

[rdavison]

One further comment for those that might be thinking about mounting a radar.  I decided to try a leveling radar mount as Ron Hill suggested and chose the radar-on-the-level from, you guessed it, http://www.radaronthelevel.com/.  My installation looks exactly like the main picture on the home page.  

After using it for a year, on balance, it seems to be working out OK.  The hight is perfect and the leveling feature works fine after you set bearing bolt tension correctly.  I had it too tight at first.  The only downside I've had is that it tends to twist the backstay junction axially.  That is, it swings around the axis of the upper backstay as well as staying level.  I may still have the hinge bolt a bit tight which will exacerbate this effect.  It is just a bit unsettling to have the backstay pulled this way and that as the boat moves.  I think this is mostly an emotional effect as the actual movement is small and applied across a long length of backstay (Ron, please comment if you see any problem with this reasoning).

I also am a ham and one other shortcoming is that I don't feel comfortable insulating the backstay and running 100 watts into it.  I think the probablilty of trouble with the radar is very high given the close coupling that would occur.  I use other antenna approaches.

Finally, seagull poop ends up right where you sit.  Not good.  At the dock, I tie bright ribbons to the main halyard so that they are right above the radar when the halyard is tied to the rear pulpit.

The radar power lead runs down the left lower stay and into the transom.

Would I do it again - I think so, unless I was pulling the mast for some other purpose.  Then I might mast mount it to allow insulating the backstay.

Randy Davison  #1268 1993 k7voe