Thursday, 29 August 2013

Sea Fog



  The latest bout of sea fog appeared while on a cruise had the undesired effect of putting the wind up my shorts instead of filling the sails. By the time I had got out toward the Spitway the fog had cleared and the sun shone pleasantly enough but was I the only skipper sailing down the river puffing his fog horn like the proverbial playground clown? I must have been because I never heard any reply. Very deadly that, silence in fog I mean. If you were sleeping in any of the trot moorings, well I hope I passed some trot moorings.., in fact any double glazed home on the whole Dengie or Tendering Peninsular and was woken in the early hours by awful wailing sounds - sincere apologies.. 

  I have since been thinking about radar reflectors and in particular how useful one would be to me if I were to install one on Shoal Waters mast. Where on the mast is to advance a stage for now and I'm just thrashing about the idea but the initial concept is beginning to interest me.  Down the creek Mike showed me a radar reflector he made using a plastic Coke bottle and filling it with balls of aluminium cooking foil. He then painted the lot white. The cost was nominal to say the least; a box of kitchen foil. But, the result was I thought it looked like one of those professional jobs on an offshore yacht only I wondered if it would actually reflect.  The whole concept is hopeless I guess unless the potential colliding vessel has a radar unit fitted. For small craft cruising inshore this is perhaps far too much kit to expect on board so for now that tense eye of the discerning watch and the metallic tasting fog horn will have to stay.
  Seriously though, the way I see it you only get hit by a ship once and in all probability it will feel like an uppercut from Mike Tyson with the result being a slow sink down to the sea bed. Where a reflector may just be of very practical use is passing Harwich at night or in the Thames for instance – even in the Colne to a lesser degree, and this year, the Crouch has become a great place to be to, if you like ships as I do, for it is also now a full working river with shipping in and out continually now serving up the Wallasea project. I am cruising in and around all these areas quite a lot and only yesterday came out the River Roach at dawn again under a veil of light mist, this time the three ships near to me in the Crouch were visible but half hour earlier, and throughout the night while at anchor, I could not see a thing for thick fog. And the day before when the fog horn blew and blew? I would not have been able to see the ships and they would probably not Shoal Waters. I guess the best defence is to stay put but while on a cruise that may mean staying at anchor in a place you chose in bright sunshine, which for many boats I see is nigh on bang in the fairway within striking range.

  What size, if any, would be worth putting up on a small sailing boat I do still wonder and have they been proven to work? I do have some evidence of a reflector working as a friend who had the lifeboat out to him said they found him because of his radar reflector. What size I did not ask at the time but from memory, as I had been on the boat, it looked like a standard white canister job. His mast was twice the height of mine too which perhaps may have improved the signal, who knows. It’s all food for more thought.

2 comments:

john button said...

There were some tests on radar reflectors a few years ago in PBO.
From what I remember, lots did not work, especially those that resembled crumpled foil in a tube.
Least worst was the corner reflector [octahedral] version hoisted in the rain catching position -ie, with a corner facing up and down and 4 corners facing out/ this means a 3 way bridle. And the biggest you can manage.
Easily home made fron thin ali sheet or expanded metal.

cheers
JohnB

Anonymous said...

A chap I used to know who was both a sailor and an expert on Radar signatures (as in Classified stuff) said that he used an Active Repeater. Absent that he recommended the largest Corner Reflector the boat could stand whilst sailing, backed up by the largest folding Corner Reflector the boat could stand whilst at anchor.

You want a big and steady reflection - if the reflection changes as the boat moves it could be filtered out as 'clutter', particularly if the set that is scanning you hasn't been reset after being detuned to remove the returns from waves in rough weather.

More info here:

http://www.yachtingmonthly.com/fileBank/yachtingmonthly/PDF/reflector_performance_ym_june.pdf

... basically the cheapest, lightest, way to go is the biggest Corner Reflector on test. You could probably make one yourself with ply and foil or similar but given the cost it may well turn out cheaper to just buy one (or two, or three...)

Some owners have also lined their radar-transparent hulls with foil, or at least the upper parts of it. Not only does this increase the RCS, when not obscured by waves, it supposedly produces a more regular signal than objects inside the cabin that might be creating a 'clutter-like' irregular signal, such as the stove (on many vessels thats the biggest reflector aboard).