The Miracle of Radar | Sailing Blog - Technical Hints and Tips - Sailing Television

The Miracle of Radar

On passage from St Martin to the British Virgin Islands…
SXM Radar2
We are up in the dark and raising anchor before dawn. It is a Caribbean morning with a salt tang blowing a flukey breeze off the beach and St Martin's distinctive lagoon behind. The high bulk of the island to the east hides the orange glow of sunrise and shades us from the trade-winds. Five large cruise ships are approaching from the southwest, steaming past us toward Philipsburg. It will be busy in St Martin today. But I am looking forward to a day at sea after our time in this bustling island.
SXM Radar1
Morning reveals a grey sky, a high grey dome of clouds with isolated heavier clouds and showers marching out of the east. Perhaps we won't have our normal trade-winds today. I flip on the radar to take a look at the approaching weather. I normally use the chart mode to see showers with the radar overlaid on the plotter in purple. Zooming out to see the surrounding islands I put the radar on its 48 mile range and there are the showers, a nice soft purple splotch coming up past St Barths . Over the next few minutes I plot the shower putting waypoints on it's centre until I see its approximate path. Looks like it will skim past us to the north, so I adjust course a bit further south to see if we can avoid it altogether.

What a miracle that we can have this technology of Radar on our boats! Radar is a system that uses transmitted radio waves to determine the range and direction of objects. Radar (from RAdio Detection And Ranging) sprung from 1900's technology and came into effective use in World War II, where it was influential in the outcome of some major battles. German aircraft were detected approaching for the Battle of Britain in 1940, and at sea the first ships with Radar had a huge advantage against those without. Imagine opposing fleets on a dark mediterranean night, one with radar picking out the opposition, and the other essentially blind!

Today's modern radars benefit from dramatic improvements on this technology. Our current unit (an 18 inch Raymarine 418HD radome) uses a miserly 60 watts. A detailed image of reflected targets up to 48 miles away but using just the power of a 60 watt lightbulb! By concentrating that power into short bursts we can shine a 4000 watt pulse and catch the reflection as far away at 48 miles!

Reduced visibility and working in the dark is another big advantage of Radar. With flukey winds we have a slow passage from St Martin 80 nm across the Anegada Passage and our planned arrival in Virgin Gorda in the British Virgin Islands slips to 9 o'clock. We know the channel having done it several times, most recently just a few months earlier, otherwise we wouldn't attempt a night approach. But even with local knowledge and the weather clearing as we near Virgin Gorda it is very nice to have the radar on again, picking up small craft, and confirming the chart as you can see the island overlaid nicely in purple.

Note also the target showing as a purple dot on the top right of the screen above. The radar shows this boat is nearly a mile north of us, so we can keep an eye on him even though he is not properly lit and would otherwise be a bit of a worry. Another nice use of the radar!

Here are a few other uses for radar…

  • Foggy conditions - extremely good in this situation it is a huge stress-reliever.
  • Picking up buoys on approach in the dark or fog (set the radar to close range for this (our Raymarine radar has a "buoy mode" with tuning set for this)
  • Confirming chart data for new areas we haven't visited - you can see the chart lines up with the "real world" as shown by the radar.
  • Confirming AIS targets as the two will overlay revealing other non-AIS targets

Radar is an extremely powerful tool for the cruising sailor.

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