RADAR: Section 4

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From: Mike (Original Message) Sent: 2/8/2003 8:59 PM

RADAR 4

Argh! Just what Greg would say. No way can we talk about the maneuvering board unless you have one -- and I have the same kind, and we can draw pictures on this site -- so on the back burner she goes. I'll admit that I use one rarely, because I normally am able to take early action to avoid a close-encounter situation. I doubt that many of the CD skippers that regularly use radar use the maneuvering board often, but most of the wise old-time skippers have one aboard and know how to use it.

The best presentation I've found on using the maneuvering board is in Bill Brogdon's, Boat Navigation For the Rest of Us. (pp. 175-183). Should you know how to use one? You bet. Buy the Brogdon book anyway because it's a great read. Another good way to go is the Weems & Plath, Radar Collision Avoidance and Current Plotting Board. I just bought a new one, and they are available for well under 20 bucks at just about any marine toy store. The directions for use are on the back of the board, and within an hour or so of easy practice you will use it just like an expert.

Another great advantage of the maneuvering board -- when you compute the course and speed of your target you can often establish bridge-to-bridge communications. "Vessel 10 miles northwest of buoy 10, course 020 speed 12, this is Tyboo, over." The target skipper will normally come back to you on channel 16 and chose another frequency. The battle is won if each of you knows what the other skipper is going to do. If you monitor the Vessel Traffic Service (VTS) channel (ch.13 locally) - if you have one in your area - you can tell from the chatter where vessels are located, and often you can identify which ones you have on your radar. On several occasions the VTS controller has directed me to make a turn for positive identification, and then given me a new course to steer to clear and pass astern of a big ship.

REVIEW

This is a good time to go back and hit a few high points, so let's start with the radar unit itself. The experienced guys are excused! If you already have a radar, read your handbook. Handbooks vary too, from outstanding, as in the Furuno and Raytheon units, to the Simrad, which was difficult for me to understand. The Simrad is an outstanding radar and has a unique 3-D presentation in addition to the normal modes, but I'm not sure what language was used to write the manual.

Radar adjustment is very important, and you should practice and get acquainted with your unit in good visibility before venturing out into the soup. Your handbook explains what each control does, but we can do a quick review here. All units have Brilliance and Gain controls. The brilliance control regulates the picture brightness, the gain control makes the receiver more or less sensitive, and makes weak returns look stronger. Adjusting the Tuning control is like fine tuning your television set. The radar receiver is originally set to the transmitter's frequency, but it will drift as the set ages, sometimes with temperature differences, and it must be tuned to the exact frequency of the transmitter. This is easily checked by watching a distant target on your screen and adjusting the tuning control to "peak" the target's return. Many of the newer radar sets have automatic frequency control (AFC) and automatic gain control (AGC), so tuning these may not be a problem for you while peaking the performance of your radar.

Most of the recent radars also have a Sea Clutter control. This reduces the receiver gain for a few microseconds after each pulse has been transmitted, then gradually restores it to its normal level. Too high a setting on the Sea Clutter control can lose close-range contacts, and close-in targets are very important to you in low visibility. Some of the new radars also have automatic sea clutter control.

A Rain Clutter control is found in most recently manufactured radars. This control clips each return so that only the leading edge of the return is sent to the display, and is very effective in enabling you to see a good sharp echo in the rain when the rain clutter obscures targets on the screen. Care must be taken with this control, because with too high a setting the weaker targets can be lost.

Heavy downpours, such is those in frontal activity, are a challenge for our little low-powered units. The 5 KW Raytheon with a 48-inch open waveguide, aboard my Lamplighter, was sometimes able to show large targets at up to a mile in heavy weather, but in that kind of weather our little 1.5 KW, or under, radars will choke. So what next? Rule 19, which you have memorized, is very specific. A point to remember -- there is no Give-Way or Stand-on Vessel in restricted visibility. Rules 11-18 no longer apply in restricted visibility, and both vessels are responsible to take avoiding action if risk of collision exists. Both are responsible to proceed at a safe speed, and to slow or stop if necessary. Both are cautioned to avoid a turn to port for vessels forward of the beam.

With the radar now of little value, fog signals are extremely important. You will probably wish you had a horn from an 18-wheeler instead of the little pressurized can, but whatever you have aboard, use it. If you hear a fog signal forward of your beam in a close-quarters situation you must slow to the minimum speed required to maintain steerage and keep on course. Your engines must be ready for an immediate reversal. In a close-quarters situation, when maneuvering is required, if the other vessel is a large ship you must do the maneuvering - he can not. Know and use appropriate fog signals!

An Interference Rejection Control is also found in most of the higher-end radar units. This one doesn't have unpleasant side-effects and normally does a good job - particularly if you are operating in an area with many other radar units.

Most of the older units only have a heading up mode, meaning that your boat's heading is straight up the screen on your display. The disadvantage of this mode is that when your heading changes, the targets on the screen also move, so if you are trying to plot and evaluate targets, they shift with each heading change. If you have a recently manufactured unit that also has a course up mode, I highly recommend that you use it. In course up mode it is easier to evaluate a potential risk of collision because the course up mode averages out the heading changes, thereby giving a better picture of the target's actions. So how do you follow the targets on your screen? The old fashioned way, still used by many, is to use a grease pencil, make a dot on your screen over the target, then another dot at some specified later time - usually 3 or 6 minutes - and you can then see the course of the target and compute the relative speed. If the dots are headed for the center of the screen (your position) you've got a close encounter coming. Our radar screens are small, so the grease pencil way is not easy, but it surely beats not doing anything. If you have variable range rings and an Electronic Bearing Line (EBL), or a cursor that can read out range and bearing, you can also place the range/bearing/time of each dot on a piece of paper, called a maneuvering board, and be able to compute quite accurately the course/speed/closest point of approach/time of closest point approach of the target.

The final point - "The responsibility for the vessel remains with the skipper at all times, and if the safety of his ship requires him to depart from the rules, then depart he must."

So that's all folks for the radar collision avoidance portion.

- - - - -

After a short rest period to catch my breath, I plan to rework all of the above to consolidate, eliminate, and make more sense of the whole thing - and later re-post it as a single "Radar" section.

Questions, comments, criticisms, additions, suggests -- all are welcome. Hopefully I can get started soon on the radar navigation section.

Dusty

From: STIMPY'S DAD Sent: 2/8/2003 9:25 PM
Dusty,
Thank you for your efforts on putting together the 4 sections on Radar and collision aviodance.
We are preparing to purchase our first Radar and your insights are much appreciated.
I feel that Radar, used correctly, will enhance our Safety on the water.
Doug on "STIMPY"

From: Sawdust Sent: 2/9/2003 9:13 AM
Thanks Doug,

You won't be sorry you bought a radar. It's a great tool, and in low vis is the best one on your boat. My radar stuff was fun to put together - very little original Dusty there, mostly reference material. Using the radar is kind of like playing golf -- you can read all you want, but gotta practice to be good. I keep mine on in good weather and always do different drills, pretending I'm in the soup.

The new radars have improved a lot in just a couple of years. If you get up this way I'd be happy to take you aboard C-Salt and we can go out and play... nothing like 'hands on' to see how all of the new toys work. And this one sure has them.

Dusty

From: Helen_O© Sent: 3/18/2003 3:09 PM
Dusty

I just want you to know that I appreciate very much what you are doing here. (Explaining radar) I'm following this thread very closely. While I don't have a radar unit yet, I hope to at some point in the near future and the information you have given will be invaluable. Keep up the good work.

Larry

From: Sawdust Sent: 3/18/2003 3:50 PM
Larry,

Thanks for the nice words. It was a fun project and I hope to be able soon to sift out the garbage and make just a one-page information sheet out of it all. If you plan any low visibility boating, radar is a must, and the brand on the box just isn't as important as it used to be. On our recent trip from Deception Pass to Olympia the trip would have been miserable without radar. In and out of rain, sleet, snow showers -- from zero visibility to 30 mile visibility -- most all of the way down. Don't know about coming back up - I was asleep up in the queen-size berth. Olympia was really great -- wonderful group of C-Dory nuts.

Dusty

From: Da_Nag™ Sent: 3/18/2003 4:49 PM
Hey Dusty,

Yeah, I noticed a lot of zero visibility while piloting your fine craft at Oly. Luckily, Brock was there to wipe the inside windows.

Sorry Dusty - you left yourself open for that one...

Bill

From: Helen_O© Sent: 3/18/2003 6:36 PM
I've never planned on "zero visibility", if I had a plan it would be to avoid it and not go out. However, zero visibility has sneeked up on me a few times. Instant panic....

Whenever you are ready, professor. In the infamous words of Ross Perot.... "I'm all ears"

From: Sawdust Sent: 3/18/2003 8:25 PM
Bill, my buddy!

How unkind, but true I'll admit. Les and I have been talking about how to cut down the condensation, but it's been the same with every small boat I've been aboard. Hot bodies (breathing, even), limited space, high humidity -- raining, etc. -- tough problem. One alternative (gee, I wish I had Da Nag Bill's bucks) is to put in a larger central system with vents on the windows and outlets throughout the boat. What the heck, a couple of grand here, a couple of grand there -- . Les got an electric 100 watt defogger that may help for the skipper, but.... all that glass is beautiful when humidity is not way high, but you know... supper nerd should have some ideas on how to solve the problem -- and leaving the door and windows open just ain't gonna hack it when it's cold.

Dusty

From: C-LionRay Sent: 3/19/2003 2:00 AM
I saw a new coleman forced air propane heater with a duct. The unit is outside and ducts in to heat tents etc. I'm not sure about marine applications but it peaked my interest as did the unlimited hot water shower.

From: Sawdust Sent: 3/19/2003 8:17 AM
New to me! Great idea I think. Could leave the unit in the cockpit and nice hot air inside... hmmmm

Thanks

Dusty