Make sure that nobody is working near the scanner and it is free from obstruction before power on a radar.
- Power on and switch the radar to Standby;
- adjust Brilliance for preferred viewing brightness;
- turn both manual Anti-sea Clutters and Anti-rain Clutters to minimum;
- set Gain to minimum;
- switch off all automatic signal suppressing and video enhancing sub-systems;
- switch radar on at medium range when it is ready;
- switch on automatic Tune;
- increase Gain until some background noises are seen all over the display;
- switch to appropriated operation range;
- select preferred display orientation and mode (ensure heading and speed inputs are corrected if True Motion Mode is used);
- adjust Anti-rain Clutters if echoes caused by rain are affecting the identification targets seriously;
- adjust Anti-sea Clutters if echoes caused by sea waves are affecting the identification of targets seriously.
Try not to use automatic suppressing sub-system if the use of manual anti-clutters control could achieve an usable display. Use automatic enhancing sub-system only if it is really necessary.
An argument on using sidelights in defining head-on situation was put forwarded in court. It was argued that both sidelights of a target involved in the risk of collision must be seen to effect a head-on situation. The argument was later supported by an oversea maritime expert. Another renowned author also seems to express similar argument in his book about COLREG as follows:
“… Rule 14 is apparently not intended to apply to cases in which, from a vessel which is ahead or nearly ahead, one sidelight can be seen, but the other is obscured. (Cockcroft & Lameijer 1996, p99)”
It could be confusing. It could be difficult to understand if one will look into the text of the rule as well as its application at sea.
Rule 14(a) stated the actions required when ships “meeting on reciprocal or nearly courses” and involved in a risk of collision. Rule 14(b) follows with examples that a head-on “situation shall be deemed to exist”. Rule 14(a) defines head-on situations by the meeting courses and the risk of collision. The text of Rule 14(b) described certain “shall be ” situations but does not seem to exclude any other encounters meeting on reciprocal or nearly courses and involved in a risk of collision. The rule has not exclude any other possible situation such as those have only one sidelight or even none could be seen.
The argument went on and suggest that Rule 14(c) will not apply at all as there will not be any doubt about a situation if only one sidelight can be seen. Thus, it will never be a heading-on situation if not both sidelights were seen at night. It can only be a crossing, Rule 15, situation if it is the case.
As shown in the radar picture on the left with true motion trails displayed, a south bound ship detected three approaching targets on her port side. These approaching targets were met on reciprocal or nearly reciprocal courses.
The north bound targets were going to pass the south bound ship with a distance ranging from less than half a cable to about two cables, about 90 metres to 350 metres. To most mariners, these targets were involved in a head-on situation with the south bound vessel if risk of collision between them was considered.
The second picture shows the visual scene when the radar picture was captured. Actually, the first radar screen is an enlarged portion of the radar screen in the second picture.
It can be seen that none of the three approaching targets was showing both sidelights. Should these approaching targets be considered as ships involved in a head-on situation? Could they be crossing targets if there was risk of collision?
Each of the vessels “shall alter her course to starboard so that each shall pass on the port side of the other” if it is a head-on situation (COLREG Rule 14). Otherwise, “the vessel which has the other on her own starboard side shall keep out of the way” as stipulated in Rule 15 if it is a crossing situation. The problem is that there is nobody with the other on her own starboard side. There is no stand-on vessel either as there was not any vessel required to keep out of the way as stated in Rule 17(a)i.
Apparently, these encounters might not be simple. Is the rule in collision avoidance at sea so complicated? There might be the problem of the rules. Perhaps, it is the problem in reading or interpreting the rules.
There were two targets being shown on the captured radar screen. AIS information from both targets were displayed graphically as triangular marks with two vectors. A solid vector was used to represent the ship’s heading. Another dotted vector was showing its course made good. The targets were also showing a ninety seconds trail in true motion.
As well, the south-east moving target near the left side of the picture was tracked with ARPA. Tracked information was shown graphically with a circular symbol and another vector.
As shown with the AIS symbol, the heading of the north-west moving target at the right upper corner was changing. Yet, its made good course was still lagging behind. The course made good calculator in the GPS receiver was taking longer time to reflect changes made by a vessel.
The heading and the made good course of the vessel south-east bound were similar. The made good course was appeared to be the same as its heading. However, the ARPA tracked course and speed of the target was still lagging behind. As indicated by the target’s ninety seconds echo trail, the south-east moving target should had it course changed for more than one and a half minute ago. Yet, the ARPA tracking system was still indicating a vector closer to its previous course. It was more than one and a half minute delay.
Due to the limited accuracy of radar detection itself, ARPA system need time to smooth its calculated outputs of tracked targets. Or else, the vector of targets could be rather fluctuated and difficult to be used. The time needed to produce a stable output is not related to processing speed. The time needed is related to the number of scans. Advance in processing power is not going to shorten the time needed. It still needs a larger number of scans for the tracker to work properly and each scan takes two to three seconds.
In summary, ARPA should work well on a slow changing ship with steady targets. ARPA will become less reliable if it is used on ships that make drastic changes in course or speed. ARPA need time to reflect changes of tracked targets. Tracked information will be reliable only if the target has been keeping its course or speed. Apparently, ARPA may not be that useful in area such as port and harbour where ships might keep changing their courses and speeds.
Navigation buoys may be considered as an object to tell if a radar system is properly setup. It has been suggested that it can be considered properly setup and tuned if buoys can be seen on-screen. Is it a reliable mean?
The reflective quality of a radar object depends on numerous factors such as material, size and shape. Amongst the others, they affect the echoed strength and returned direction of radar pulses.
Navigational marks are normally made with steel. In the contrary, those sampan and fishing boats in the picture are constructed with fibre-glass and wood. The reflective quality of these sampan and fishing boats are far inferior to those of steel navigational buoys. The echoes strength of these sampan and fishing boats should be much weaker than those of buoys.
As illustrated, a navigational buoy on the left is not a small object in comparison to sampan and fishing boats. Buoys are taller than most of the small boats in the photo. Apparently, the navigational buoy should have greater chance in reflecting detectable signals.
It may be argued that a can or cone shaped buoy is a poor radar object due to its rounded structure. Except the base that provides buoyancy, a buoy is normally made out of steel frame. Very often, radar reflector is fitted on the top. It appears to be a conspicuous radar object.
In fact, navigational buoys are designed to be picked up with eyes as well as by radar at a reasonable distance. Navigational marks are rather good radar objects in comparison to small boats. Apparently, the detection of navigational buoys will not assure the signals echoed from small objects such as sampan can be detected.