What is the most important use of the radar during navigation especially during restricted visibility?

Real life case: The necessity of a careful ship navigation in restricted visibility areas

In restricted visibility conditions caused by fog, off southeast coast of Miura Peninsula, Kanagawa Prefecture, a Japanese registered tug, with 5 crew (Japanese) and a Filipino registered general cargo vessel, with 25 crew (Filipino) neared each other, culminating in a collision between the two vessels, 5.4 miles from Tsurugi Saki Lighthouse on April 13, 2006, with the bow of the tug smashing into the port forward part of the general cargo vessel, leading aft on the latter. As a result of the collision, the tug sustained a crushed bow and the other vessel suffered a hole in the shell plating in the port forward section and sank, as water entered through the hole.

Actions to be taken

The master should be informed and after that the engine room should maintain the engines to be ready for an immediate maneuver.
It would be necessary to close all the watertight doors and openings, shut the ventilation fans and accommodation and engine room ports.
The manning level on bridge should be increased and if it is required and there is plan allowing it, an additional bridge team personnel can be provided.
The crew must prepare the relative equipment as appropriate, and always be sure that some tools (AIS, echo sounder, fog signaling apparatus, navigation lights, radar, ARPA and VHF) are ready to work, if needed.

Except from these actions, such situations demand the compliance with some of the COLREG-International Regulations for Preventing Collisions at Sea, specifically:

COLREG Rule 19 – Conduct of vessel in restricted visibility
COLREG Rule 35 – Sound signals in restricted visibility
COLREG Rule 5 – Look-out
COLREG Rule 6 – Safe speed

Last but not least, there should be a contingency plan which ensures that the ship will be ready to reduce speed, stop and turn away from danger or if it is possible to anchor, in case of emergency during ship navigation.

A valuable checklist to ensure safe ship navigation in restricted visibility

A useful checklist aiming to provide information in order to be sure that such actions have been followed properly during ship navigation, like the one provided by SQE MARINE herebelow could be helpful

BRIDGE PROCEDURES: Read in this series

During periods of restricted visibility (such as rain, mist, heavy fog, or hours of darkness), you should slow to minimum speed to give your vessel an opportunity to maneuver should the risk of a collision arise.

WHEN VISIBILITY IS RESTRICTED BY FOG OR SMOKE, ADDITIONAL SOUND SIGNALS ARE REQUIRED:
VESSEL TYPE	SITUATION	SOUND REQUIREMENT
Power Vessel	Underway	Prolonged blast every 2 minutes
Sailing Vessel	Underway	Prolonged blast + two short blasts every 2 minutes
Power Vessel	Underway but not moving	Two prolonged blasts every 2 minutes
Any Vessel	Anchored	5 seconds of rapid bell ringing every minute
Any Vessel	Run aground	3 bell strokes + 5 seconds of rapid bell ringing + 3 bell strokes every minute

Unless the risk of a collision is present, you should reduce your speed to the minimum you need in order to keep on course when you hear any of the sound signals above.

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Ship navigation under restricted visibility circumstances is one of the most challenging tasks while accomplishing a safe voyage. The visibility is mentioned as restricted in cases that have been observed fog, heavy rain, or dust storm, all hazardous conditions to navigate. Ship navigation in such conditions doubles the likelihood of a collision or grounding. It calls for the use of specialized equipment and requires some actions to be taken by the time the ship's officer gets information of relevant weather conditions. Restricted visibility conditions mean those in which the visibility is Three Nautical Miles or less, or is not more than that designated separately by the Master. Conduct of the vessel's navigation in restricted visibility is covered in COLREG Rule 19. The watch's officer should take the following actions under restricted visibility conditions or if such conditions are expected:

Inform Master, report existing conditions
Intensify watch of surrounding conditions, e.g. by posting additional lookout(s)
Comply with latest International Regulations for Preventing Collision at Sea
Inform engine room and sound appropriate fog signals.
Take other necessary action mentioned in the “Navigation in Restricted Visibility Checklist"

Master's action under restricted visibility conditions When receiving the report from O.O.W., that restricted visibility conditions are present or expected, Ship-Master shall confirm the navigation situation and, if necessary, shall take the command of the ship. The Master must ensure that all watchkeepers understand the use of safety-related equipment before keeping a watch. Master should take appropriate measures as needed such as posting additional Lookout (s), Reduction to a safe speed, etc.

It is vital that an efficient lookout is maintained by the O.O.W. ensures at all times. In a ship with a separate chart room, the O.O.W. may visit the chart room, when essential, for a short period for the necessary performance of his navigational duties. However, he must previously satisfy himself that it is safe to do so and ensure that an efficient lookout is maintained. A continuous visual lookout all-round the horizon, and a listening watch (including both sound signals and radio messages) is to be maintained at all times. A constant watch solely by radar is not acceptable as an efficient lookout. During the hours of darkness and restricted visibility, a rating must be appointed Lookout in addition to the O.O.W. He must remain on the bridge for the entire duration of his watch and may only leave the bridge, having first been relieved of his post.

In maintaining a lookout, the following shall be observed:-

The Lookout must be able to give full attention to the keeping of a proper lookout, and no other duties shall be undertaken or assigned which could interfere with that task;
The duties of the Lookout and helmsman are separate, and the helmsman is not to be considered as the Lookout while steering, except in small ships where an unobstructed all-round view is provided at the steering position, and there is no impairment of night vision or another impediment to the keeping of a proper lookout;
The O.O.W. must ensure that lookouts clearly understand their duties and the system of reporting. All reports must be passed to the O.O.W or the Master when it has taken over CON. If a pilot is on board, he should be informed as well.
At the discretion of the Master, the O.O.W. may be the sole Lookout in daylight under certain conditions provided that:
The situation has been carefully assessed, and it has been established without doubt that it is safe to operate with a sole lookout.

Full account has been taken of all relevant factors, including but not limited to the following:

State of weather
State of visibility
Traffic density, including the presence of fishing vessels
Proximity of dangers to navigation
The attention required when navigating in or near traffic separation schemes

It must be remembered that conditions can change at very short notice, and therefore the O.O.W. must be able to summon the additional Lookout immediately if the situation requires. Accordingly, the rating allocated to be the additional Lookout must be either on stand-by or working within the vicinity of the bridge and be immediately contactable.

Below is additional check items during ships navigation in or near an area restricted visibility

Have conditions been reported to the master?
Have lookouts been posted properly and increased as required?
Have engineers been given notice (for stand-by engines)?
Are Radar / ARPA in operational condition?
Has tuning been adjusted to the optimum condition?
"Has range been set to the proper scale? - X-Band (3cm) for short dist, S-Band (10cm) for long dist"
Are other vessels (moving objects) plotted properly?
Has manual steering operation been checked?
In congested waters, has the steering system been changed over to manual operation?
Have the navigation lights been switched on?
Is VHF listening watch maintained on Ch16 and a proper channel stipulated by local rules?
Is the vessel proceeding at a safe speed according to COLREG?
Are appropriate fog signals being sounded?
Vessel making way through the water: One long blast at not more than 2 min intervals
Vessel making no way through the water: Two long blasts about 2 sec apart, separated at not more than 2 min intervals
Vessel not under command / restricted in ability to maneuver / constrained by draft: One long blast followed by two short blasts at not more than 2 min intervals
Any additional instructions from the Master

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