Radar reflectors, sailing in fog

June 13, 2008   

Several things effect how far away a vessel can be seen this is not a complete list but are the easiest to explain

1)output power of the unit a 16 mile radar is 1.5KW and a 24 mile unit is 3KW

2)heel angle at 15 degrees anything to windward is invisible and there is a significant blind spot to leeward unless the scanner is on a self leveling system

3)scanner height e.g. scanner is 5m off sea level and the target is 15 meters high the radar horizon is 13.5 miles away

4)atmospheric conditions

Radar reflectors some important points

1)mast shadowing – where ever it is mounted there is typically a 10 degree blind spot aft of the mast if it is mounted on the front. With movement of the vessel however, the return will be pretty consistent of at least 5 miles.

2)Material – some materials absorb (fiberglass absorbs 50% of the beam) others like steel and aluminum reflect even if there is some reflection it might be so erratic that it can”t be monitored on the screen.

3)Standards – 10 m2 is minimum in US reflectors must show range of 4 nm in calm sea.

4)Type –click here for the MAIB commissioned report on radar reflectors and also the MCA Guidance document

a)the octahedral if they are less than 18” wide are useless, shouldn”t be hoisted by the corner and even when it is hoisted correctly they have a blind spot of 120 degrees increasing to 180 degrees when heeled under sail you have a 50/50 chance of being seen

b)the mobri cylinders show nothing at all

c) if you have power and the money go with a Sea Me system it is the best on the market

c)RYM buys Echomax 230 I Inflatables see http://www.echomax.co.uk/Echomax_Products.htm

RCS Peak m2 24m2 April 2001 6.3m2 Nov 2001 7.96m2
Response below peak 12 peaks 20m2 @ 30 Degree intervals Peaks – 4m2 & 5m2
Performance @ 1.25m2 100% 100%
Performance @ 2.5m2 100% 54%
Performance @ 5m2 100% 8%
Performance @ 10m2 70% zero
+ or – 3 Degrees heel 24 sq.m @ 2.5m2- no nulls 7.96 Seven nulls exceed 10 Degrees
+ or – 9 Degrees heel 19 sq.m peak @ 2.5m2 no nulls 7.0 Seven nulls 28.5% (102.6 Degrees)
+ or – 15 Degrees heel 9 sq.m peak 7.0 Seven nulls 45% (162 Degrees)
+ or – 20 Degrees heel 5 sq.m peak Not tested
Overall length 610 mm 595 mm
Diameter 248 mm 240 mm
Distance between centres EM-230 560 mm
EM-220 BR (17m2) 545 mm
545 mm
Weight 2100 gr 1879 gr

The above test results were obtained at QinetiQ (DERA) in April/November 2001 and May 2002.

7: Try to keep it vertical so if you are sailing and heeled over have two down lines one on each toe rail and you can use these to counter the heel to some extent.

The important things to do in fog is

1)The GPS can be more than 50 feet off so it is best to leave things at least ¼ mile off unless you have a radar

2)Keep moving don’t stop but go at a safe speed (rule 6)

3)Cross a shipping lane at the shortest point and as close to 90% as possible if you have to

4)Keep extra look out

5)Officially you should sound signals (I didn’t have it on the air horn yet but normally I tape the following onto the canister)

1.Long. Under power, making way (sound every 2 minutes)

2.Long, long. Under power, not making way (sound every 2 minutes)

3.Long, short, short. Towing, fishing, restricted ability to maneuver, sailing, and NUC (sound every 2 minutes)

4.Long, short, short, short. Manned vessel being towed (sound every 2 minutes)

5.Bell for 5 seconds At anchor (sound every minute)

6.Short, short, long. You are running into danger (also 5 shorts)

BTW: Number 6 is what I would expect to hear from that ship we were close by in the entrance to the bay if he had thought there was a problem…

6)Have the engine started

7)Listen on channel 16 and 13 in dual watch (I believe we were listening to 16 but not 13) 13 tells us vessel movements

8)Everyone with lifejackets on

9) Make Securite call on VHF if necessary

10)Alterations of course in general should be avoided after hearing a fog signal forward of the beam unless both position and movement of vessel have been determined as you could possibly present your boat into a t boning situation. See http://books.google.com/books?id=dgK3XYYhjeIC&pg=PA136&lpg=PA136&dq=altering+course+in+fog&source=web&ots=_0t80EgIUh&sig=kz90z9CZGlZP7PdOH9y2arIqbYU&hl=en&sa=X&oi=book_result&resnum=2&ct=result#PPA139,M1�

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