At the last two London Boat Shows, there has been a fog tunnel, sponsored by Raymarine. The feature, designed to help yachtsmen get to grips with radar, has proved overwhelmingly popular.
Talking to visitors to the exhibit, Raymarine staff were surprised to discover just how many had radar fitted to their yachts, but little understanding of how to use the equipment to best effect.
So a notice went up on the company's website offering free radar tuition at its Portsmouth HQ, and within two days not only had all the places been taken, but there was a huge waiting list, too!
So Raymarine put on a course for yachting journalists, in the hope that we would help to make the knowledge more widely available. So over the next few weeks watch out for a series of articles on making the most of your radar.
The RYA offers a radar course, but apparently uptake is disappointing, which is in a way surprising, as the cost of the course (about £100) is relatively minor compared with the cost of installing radar on the boat (from about £1,000 each for scanner and display, on Raymarine's price list).
Perhaps it's because people look at the manual and think it will tell them everything they need to know - and then the good intention to work their way through it falls by the wayside.
“I am not being disparaging about yacht owners,” said Alan Watson, an independent radar specialist, who led the course, “But you'd be surprised how many have got all this fancy gear on their boats and haven't got any idea of how to use it. They look on radar as a sort of Captain Kirk force shield: as long as you switch it on it will protect you. It won't if you don't know how to use it!”
Yacht radar does use a lot of battery power, and therefore it is tempting to keep it turned off except in emergency. But then when the fog descends, the user is unfamiliar with the display, and does not fully understand how to interpret it.
So it's a good idea to switch the radar on when you are motoring, and keeping the batteries charged is not an issue, and practise using all its different functions until you are thoroughly familiar with them.
“Playing” with the radar in good visibility gives the opportunity to identify each echo - this small one is that buoy, this big one is that anchored ship, this fast-moving one is that pilot launch, and so on - which helps with interpretation when fog does descend.
But of course radar is not only useful in fog. It is also useful for position fixing and pilotage, operating entirely independently from GPS, which could come in very handy if and when GPS is jammed or otherwise disabled.
And radar is useful for collision avoidance, not only in fog, but also in clear visibility. Crossing busy shipping lanes like the TSS in the Dover Strait, for example, every target can be assessed for range and bearing and collision risk, much more accurately using radar than with a hand-bearing compass.
So what is radar, and how does it work? The scanner can be either open array - a straight bar that revolves, as seen on large ships and shoreside installations - or a radome - the circular container more commonly seen on yacht masts, which also contains a revolving antenna.
This works by firing a short pulse of radio energy and then listening for reflections coming back. The antenna forms the pulse into a fine beam, and the bigger the antenna, the finer the beam and the sharper the picture.
How well an object shows up depends on a number of factors:
Size
The bigger the object, the better the echo. Small objects like buoys can be lost in “sea clutter” when conditions are rough.
Material
Electrical conductivity affects the strength of the reflection. Metal gives a good reflection, GRP a very poor reflection. Carbon fibre is “somewhere in the middle,” said Alan.
Aspect
The radar pulse can be deflected from a target as from a tilted mirror. The flat sides of a ship will give a strong echo. The sloping angles of the bow of a ship heading straight towards you will give a weaker return.
Surface irregularities
“Stealth” aircraft are invisible on radar because their complex angles break up the radar pulse so that it does not return. Irregular shapes do not show up well on radar.
Small craft do not show up well, hence the requirement for a radar reflector. Alan Watson explained that the idea that radar can “see” for example a yacht's engine is mistaken.
In radio terms GRP is a “lossy” material, he said. This means that the radar cannot see it - and cannot see through it either. In effect the mast is the only thing a ship's radar is likely to see, and that is an extremely small target.
Radar reflectors improve the chance of the yacht being picked up on a ship's radar, although most only work to their optimum when vertical. Alan also pointed out that ships' radars may have blind spots, where they could not see that yacht, no matter how good its radar reflection.
Some large container ship have an extra radar on the bow, to see the area obscured from the bridge, and also from the masthead radar, by the height of the cargo on the deck, but even it was fitted, it didn't necessarily mean that anybody was looking at it, Alan pointed out.
“The space between a bow and one mile ahead of the ship is not a good place to be!”
Equally, ships' funnels could leave a blind arc on their radar screen, and cargo derricks etc would interfere as well: “They won't have 360 degree radar coverage.”
And nor do yachts: there is a blind spot caused by the mast, which may be directly astern, in the case of a radome mounted on the front of the mast, or ahead, in the case of a radar mounted on a pole at the back of the yacht.
An increasing number of radomes are mounted on the side of the mast (as ours is.) This is because it is often an easier place to fit it according to the mast section, and it also reduces wear on the genoa when tacking.
It may be no greater disadvantage to have a blind spot to one side than directly behind, but it is important to know where the blind spot is, and to be aware that not every potential danger will show up on the display.
Radar is an aid to navigation, but it is only an aid, Alan Watson concluded.
