Valiente brings up some excellent points. Years ago my uncle, sailing on the great lakes, asked me which item I would recommend; radar or GPS/chartplotter. As I recall, they were much closer in price to each other in those days. I recommended the radar. In my opinion, radar is the single greatest navigational tool to come down the pike since celestial navigation. The reason I rank it ahead of RDF, Loran, GPS, etc...is that it functions best where precise navigation is needed most.
On a small sailboat radar is not of much use for collision avoidance. The limited range and slow speed of the sailboat combine to allow the sailor a relatively short period of time to "see" what is about to hit him. For collision avoidance alone, a radar reflector or, better yet, a radar transponder is much less expensive and much more effective. The approaching vessel will see you long before you pick up a reliable echo and make an alteration to pass you well off the beam. "Sea return" limits the close in effectiveness of any radar and it is magnified on a vessel with it's radar mounted close to the water. For computer operated collision avoidance one must dial out the sea return, as well as rain return, to avoid tracking waves/squalls. Generally speaking, the level of reduction in "gain" to dial those out tends to also dial out such things as buoys and small craft. So the CAS function of radar is limited. To be truly useful one must monitor the radar, and tune the unit, as if one were not using the CAS. Employed in that manner, it is a great tool. The warning rings on the CAS are not only next to useless, they are dangerous. Their presence on the unit implies an automatic function that should actually be done by the operator observing the scope. To the extent that the operator believes an alarm will go off if a vessel penetrates his ring the system is dangerous.
The navigational advantage of radar, whether ship or boat mounted, is that it is most effective at distances and conditions when position finding is critical. As one traverses Lake Michigan it is not necessary to know ones position to an accuracy of less than two miles, and the same holds true offshore. And if one is completely befuddled, sailing west is generally going to run you into Wisconsin. With radar you are not going to collide with Wisconsin and, coupled with a good chart drawer, it's pretty simple to figure out which Wisconsin barn you're pointed towards. So, in short, the radar gets you offshore safely, clear of any navigational hazards, and becomes effective just when you need it when returning from sea.
One more caveat on collision avoidance with radar. You're approaching the port of Kenosha, in fog, but have a good fix and you're getting ready to put her between the buoys. There's a decent sea running and the VHF is full of chatter between the Mesabi Miner and some tug boats. You observe on radar what looked to be part of a pier is now moving. This might be a good time to use the radar for collision avoidance by heaving to offshore, preferably adjacent to the buoyed channel. With the sea running, the 1000' ore boat is going to lose anything small from 3-5 miles away on radar. Even though you see her plain as day, it may not be wise to enter the channel if she doesn't see you. And they may see you offshore but lose you in the clutter as you get closer. This might be a good time for a fresh cup of coffee and a half hour adrift until she clears the channel.
Valiente mentions another good point. You pick up a return with a return close to it that comes in and out, or appears much smaller and on the same course. Steering well clear of both would be prudent. They may be two seperate vessels or they may be two seperate vessels connected by 1000' of 3" steel cable. Could ruin one's day and all that.
The beauty to a radar presentation versus the GPS/plotter presentation is that you are looking at what is actually out there, versus where the GPS/plotter says you should be and where the buoys "were" when the plotter's software was manufactured.
Much of seamanship and navigation comes down to a simple safe or not safe equation. If your engine conks out and you are busily changing a filter, you don't care where you are at, only that you're safe. A quick glance at your radar tells you you're 7miles off the beach and have time to change the filter. Or it tells you, you're 2 miles off the beach and might want to walk out the hook before you go below to tackle the filter.
If you treat radar like an extra set of eyes, and realise that it doesn't make you Superman with X-ray vision, you'll probably agree with me that it's the best thing afloat other than a good cook.
Last edited by sailaway21; 12-25-2006 at 12:09 PM.