a radar question

[Bill Stebbins]

Does anyone know if a small radar display will cause significant compass deviation if the radar is within about 6 inches of the compass? Will GPS affect compass deviation under the same circumstances? I have a small shelf on the bulkhead where all these instruments sit in my CD 28 FB.



stebbins@umich.edu

[john churchill]

current in parallel wires creates an electromagnetic field which can affect your compass. the powere and ground wires ought to be twisted if they are within a few feet of your compass. the more current the larger the effect.
john

[Stu Timm]

Does anyone know if a small radar display will cause significant compass deviation if the radar is within about 6 inches of the compass? Will GPS affect compass deviation under the same circumstances? I have a small shelf on the bulkhead where all these instruments sit in my CD 28 FB.

Hello Bill,

I think that radar screens, even small ones are essentially television (video) crt's, or cathode ray tubes which have powerful magnets in the rear of the tube. These (or any magnet) located near a compass will generate varing levels of deviation. John's posting of twisting all wires is correct to cancel out the small fields generated by current flowing through the wiring in your helm console.

The radar screen will generate further deviation if it is close to the compass. If there's no way to place the radar farther away from the compass, try to set up a compass deviation chart.

Try turning circles with your boat under power on a calm day against a known reference like a church spire, chimney or range. Take relative bearings on that reference with a peloris (hand held) and compare them against what your compass is telling you. That will give you a reasonable idea as to what deviation to add or subtract from your magnetic readings.

Happy navigating!

Stu Timm




mitshu@juno.com

[Catherine Monaghan]

Bill,

According to "Coastal Navigation" by Mike Pyzel, due to thier electromagnetic fields, electronics should be installed 3 or more feet away from the compass. Your radar, only 6 inches away, will definitely have an effect on the compass while it is operating.

catherine_monaghan@merck.com
CD32 Realization, #3
Rahway, NJ
Raritan Bay
<a href="http://www.hometown.aol.com/bcomet/real ... lization's Home Page</a>

Does anyone know if a small radar display will cause significant compass deviation if the radar is within about 6 inches of the compass? Will GPS affect compass deviation under the same circumstances? I have a small shelf on the bulkhead where all these instruments sit in my CD 28 FB.

catherine_monaghan@merck.com

[Tom Shelford]

Does anyone know if a small radar display will cause significant compass deviation if the radar is within about 6 inches of the compass? Will GPS affect compass deviation under the same circumstances? I have a small shelf on the bulkhead where all these instruments sit in my CD 28 FB.

Hello Bill,

I think that radar screens, even small ones are essentially television (video) crt's, or cathode ray tubes which have powerful magnets in the rear of the tube. These (or any magnet) located near a compass will generate varing levels of deviation. John's posting of twisting all wires is correct to cancel out the small fields generated by current flowing through the wiring in your helm console.

The radar screen will generate further deviation if it is close to the compass. If there's no way to place the radar farther away from the compass, try to set up a compass deviation chart.

Try turning circles with your boat under power on a calm day against a known reference like a church spire, chimney or range. Take relative bearings on that reference with a peloris (hand held) and compare them against what your compass is telling you. That will give you a reasonable idea as to what deviation to add or subtract from your magnetic readings.

Happy navigating!

Stu Timm

You are right on Stu except now you need another chart to use when the radar is off.Bill I suggest on the cd 28 in the cabin,mount it on an overhead mount or on the fly bridge coaming as far left or right as you can get it



TShel11523@aol.com

[Art]

Does anyone know if a small radar display will cause significant compass deviation if the radar is within about 6 inches of the compass? Will GPS affect compass deviation under the same circumstances? I have a small shelf on the bulkhead where all these instruments sit in my CD 28 FB.

I have a 28 FB hull# 33 with the Lcd type screen right next to the compass with no problems. I would not recomend the old tube type near it. But as I have a 28 I know there is only room fore a small radar display. On the other side of the compass I have a gps mounted.



KEARConner@aol.com

[Walt Bilofsky]

I've gotten various pieces of equipment closer than I thought possible to compasses without much effect. And from what I know of electronics, I think it's quite possible you could get away with the LCD display six inches from the compass. Unlike a CRT, the LCD is low current, low voltage, and doesn't have magnets. The real power in the radar is consumed in the dome.

All that power does go through the display unit, of course. So John's caution about routing the power leads is correct. I'd worry more about keeping the wires away from the compass, and then twisting or even shielding them. Probably the cable to the dome will already be shielded.

This is all speculation, of course. It would be best to try it out before mounting permanently, and have a fallback scheme in mind. It wouldn't suffice to jury rig the display to power leads and put it into demo mode - you'd need to wire it to the dome in order to get the power going through it. But maybe you could wire it all up and test the configuration before actually installing or cutting stuff - see if the compass does anything when you turn the unit on and start transmitting.

I often buy from my local marine electronics dealer, even if it's a bit more money. They have the experience to answer questions like this.



bilofsky@toolworks.com

[Pete Asensio]

imho, you will experience little or no interference from
an LCD radar display. I have one in my CD 28 Open, and I have
yet to note any effect on the compass, although my unit is
farther away from the compass. Walt's suggestion to try it before
drilling holes is right on...



pase@uconect.net

[Catherine Monaghan]

Does anyone have any experience with any of JRC's (Japan Radio Co.) radars? Their LCD Radar 1500 looks interesting and is priced right.

catherine_monaghan@merck.com
CD32 Realization, #3
Rahway, NJ
Raritan Bay
<a href="http://www.hometown.aol.com/bcomet/real ... lization's Home Page</a>

Bill,

According to "Coastal Navigation" by Mike Pyzel, due to thier electromagnetic fields, electronics should be installed 3 or more feet away from the compass. Your radar, only 6 inches away, will definitely have an effect on the compass while it is operating.

catherine_monaghan@merck.com
CD32 Realization, #3
Rahway, NJ
Raritan Bay
<a href="http://www.hometown.aol.com/bcomet/real ... lization's Home Page</a>

Does anyone know if a small radar display will cause significant compass deviation if the radar is within about 6 inches of the compass? Will GPS affect compass deviation under the same circumstances? I have a small shelf on the bulkhead where all these instruments sit in my CD 28 FB.

catherine_monaghan@merck.com

[Walt Bilofsky]

Does anyone have any experience with any of JRC's (Japan Radio Co.) radars? Their LCD Radar 1500 looks interesting and is priced right.

Catherine -

JRC used to make Raytheon's radars, including the one on my boat. The first unit I had went bad, but it was a brand new model, Raytheon replaced it, and it has worked pretty good ever since.

Powerboat Reports reviewed three radars in September 1998, including the JRC 1000. It came in last, but it is a $900 1.5 kw 16 mile radar and they were comparing it to two 2 kw 24 mile radars priced at $1500 to $2000. They marked it down for small display size and power, lack of a drain plug in the dome, and putting the electronics in the dome which makes servicing a pain.

I can attest to that last because my JRC-built Raytheon radar is the same, and servicing is very much a royal pain. And I don't have to go up a mast to do it. I didn't realize that other radars might not have as much electronics in the dome, but if that's true, then I would certainly rule JRC out for a sailboat.

In general, PBR likes Furuno, and considers Si-Tex if you want value rather than features.

- Walt



bilofsky@toolworks.com