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| RADAR ADVICE
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October 12, 2005. I hang out on an interesting and informative trawler web site, and recently read this item by Capt. Mike Maurice, a delivery skipper from the Portland, Oregon area.-- Bob Hale
In Bodega Bay the other day I was talking with a novice sailor who complained about all the fish boats that did not show up on his radar. I mentioned that while coming up the coast from Ventura, California, we had used the 1.5 mile range to spot boats, and that sometimes the smaller boats did not show until they were about a mile out, even using such a short range. That's when I found out that he was using the 8 and 12 mile ranges.
There is NO magic in radar. It is all simple physics and line of sight issues. In other words, more power means better echos. Moving the radar antenna higher results in more range, but only to the distance to the horizon, which increases slowly and does not double as the radar’s height doubles. Keep in mind that as the antenna is raised, the zone near the boat that will not return echos also increases. At 60 feet up the "dead" zone around the boat is about one-thirteenth of a mile in radius or about 500 feet.
If I had a radar with a 1/8 range scale and wanted to see objects within 60 feet of the boat, I would not have the antenna higher than about 15 feet. You may be able to visually see a sailboat's sail and 60-foot mast at 10 miles, but you can't bounce a radar signal off of them until they are about a mile away or less, assuming a 4 kw transmitter. The hull, however, will return echos, IF the hull is above the physical horizon, which might be as much as 3 miles with a typical 40-foot sailboat.
Never use a radar range greater than necessary for the task at the time. For targets other than large ships or fishing boats, the highest range I would use is 3 miles. If you suspect high speed large targets, they will show at 8-12 miles. It might be useful to spot them at those ranges, but usually it’s not a necessity. I like to use 3 miles and offset our boat back about 1.5 miles to the rear of the display, which keeps the radar in 3 mile mode but shows things 4.5 miles out. If I then switch to 6 miles, the display will show things out to 9.5 miles. Generally, this should be done for short intervals only. It’s a system that has worked well for me over the years.
BTW, I am not a fan of radar reflectors. The little ones we use won't show well on "S" band radar used on the big ships. They may be running their "X" band stuff if they suspect we little guys are around, but don't count on it. I would not count on the radar reflector being effective on some other boat and unless properly aligned in the "catch-rain” position, not even the one on my boat.
Capt. Mike Maurice
Tualatin (Portland), Oregon
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