According to the International Regulations for Preventing Collisions and the illustrated lights, what type of vessel is it?
This vessel is not under command and stopped in the water.
This is a vessel constrained by her draft.
This vessel is not under command, but is making way through the water.
Two ships travelling in opposite directions are to pass each other in a narrow river, as illustrated. Explain what is likely to happen as they pass each other?
Due to interaction, the bows will repel each other, and then when alongside each other the two ships will be sucked together and finally the sterns will be repelled as they start to pass clear.
There will be very little effect between the two ships as they pass.
Due to interaction, the bows will attract each other as they approach, then they will repel each other alongside and as they pass clear, the sterns will be attracted.
As they approach, rudder should be applied quickly to avoid sheering into the path of each other. Then as they are alongside they will be attracted and finally repel each other as they pass clear.
The ship is navigating in dense fog where the visibility is less than one mile. The Arpa radar is set on a range 12 miles on a course of 314° and own ship has a vector as shown. What is the vector mode selected on the Arpa?
Relative vectors, ground stabilised.
Relative vectors, sea stabilised.
Which part of the magnetic compass error changes with a change in the course steered?
All of the suggested answers.
Which of the answers best summarises the information which should be provided for the bridge Officer of the Watch within an effective Voyage plan?
Courses to steer; distance off dangers; parallel index lines; expected currents; prevailing winds; distance between alteration points.
Expected prevailing wind and weather.
Contingency arrangements in case of problems.
All of the suggested answers.
What corrections must be applied to the echo sounder reading to compare the depth of water with the depth printed on the chart?
Allowance for the ships speed.
The distance between the pulse Transmitter and Receiver.
The IMO Standard Marine Communication Phrases are recommended to be used when the ship’s Officer is verbally talking to whom?
When talking between ship and shore personnel.
In circumstances described in all of the answers provided.
When giving orders on board with other seafarers.
When talking on the VHF between ships.
If a DSC distress alert is received on board your ship, what is the first action that should be taken?
Immediately answer the distress message on the correct radio frequency.
Contact SAR Authorities via nearest coast Radio station.
Listen for a distress message on the appropriate radio frequency for five minutes.
Determine how close your vessel is to the distressed vessel.
What is understood by the term “Dew point” of the air?
All of the suggested answers.
The “Dew Point” is the point at the centre of an Anticyclone.
The temperature of the water vapour in a cloud.
The temperature at which water vapour in the air forms into water droplets.
How can an ARPA assist the ship to steer a suitable course to make good the entrance to a channel?
Select Relative motion display and make Own Ship vector pass through the middle of the entrance to the channel.
Acquire the buoy at the entrance to the channel and on relative vector display alter course to make the vector of the buoy pass directly through the centre of the screen.
Select True ground stabilised vectors and make the vectors from both buoys at the entrance to the channel pass either side of the centre of the screen.
Select ground stabilised true motion display and alter course so that own ships true vector passes through the middle of the entrance to the channel.
In the diagram, the amount of water under the keel is indicated by the letter “C”. Which bridge instrument would measure this value?
Which of the four figures illustrated shows the correct position line for the following situation: Latitude 50° 00′ N, Longitude 30° 00′ W, Time 1200 GMT. Course steered: 090° True, Speed: 12 knots, bearing of the sun: 200°, Intercept correction: 00° 02′ Towards (observed altitude – computed altitude).
How can the effects of Squat be minimized, when a ship is proceeding in shallow water?
Maintain a speed of about 6 knots and use minimal rudder when manoeuvring.
Enter the shallow water with a stern trim and proceed at a moderate speed.
Decrease the speed and keep this ship to the centre of the channel where the water is probably deepest.
Maintain a slow speed just sufficient to maintain steerage.
What do the shapes that this vessel is displaying tell us about her?
That she is not under command.
That she is engaged in towing.
That she is restricted in her ability to manoeuvre.
That she is constrained by her draught.
Why should Ground Stabilised True Motion display mode be avoided when using the ARPA for anti-collision purposes?
The collision regulations are based on ship courses through the water.
The true vector can never give an indication of collision risk with another ship.
True motion does not provide the collision risk of other ships.
The Relative Motion display and relative vectors is the only display to use for anti-collision purposes.
What is the correct understanding of the term “Block Coefficient” as applied to a ship?
The restriction of a valve in a pipe to the flow of fluid through that pipe.
The coefficient of a Block and Tackle.
The comparison of the underwater shape of the ship, to a rectangular block of the same extreme dimensions.
The ratio of the water plane shape of the ship to a rectangle of the same extreme dimensions.
You are proceeding along a coastal route when you hear this signal. The visibility is severely restricted. What does the signal mean?
There is a vessel aground in the vicinity. She is more than 100 metres in length. She is sounding an additional warning to approaching vessels, directing them to “keep clear”.
There is a vessel aground in the vicinity. She is less than 100 metres in length. She is sounding an additional warning to approaching vessels to “navigate with extreme caution”.
There is a vessel aground in the vicinity. She is more than 100 metres in length. She is sounding an additional warning to approaching vessels that they are “running into danger”.
There is a vessel at anchor in the vicinity. She is less than 100 metres in length. She is sounding an additional warning to approaching vessels that they are “running into danger”.
How will the ship behave if it experiences a complete loss of power (black out) in the situation illustrated?
The wind will push the vessel sideways, but the heading will not change.
The vessel will gradually swing to port and the speed will slowly reduce.
The vessel will continue on course and the speed will slowly reduce.
The vessel will gradually swing to starboard and the speed will slowly reduce.
Where can a ship expect an act of piracy to take place?
At the south end of the Red Sea.
Is the location of the Compass Binnacle critical?
Yes, for the reasons stated in all of the suggested answers.
Yes, it should be sited on a non-metallic base if possible.
Yes, it should be on the fore and aft centreline of the ship.
Yes, it should be away from all electrical power cables.
The position of the ship is found by taking a series of bearings using a magnetic compass. How should an error of 5° WEST be applied to the compass bearings?
The error should be “High” or “Low” and therefore more information is required.
Add the 5° to the bearings.
Subtract 5° to the bearings.
The same error applies to all bearings and therefore it can be ignored.
What is the direction of wind associated with an anticyclone (area of high pressure) in the Northern Hemisphere?
Straight towards the centre of the anticyclone.
Directly away from the centre of the anticyclone towards the nearest Low pressure.
Anticlockwise around the high pressure.
Clockwise around the high pressure.
According to rule 12 of the International Regulations for Preventing Collisions, in the situation illustrated, which sailing vessel (A or B) must keep out of the way of the other?
Sailing vessel A must out of the way of sailing vessel B.
Both sailing vessels are required to take avoiding action.
Sailing vessel B must out of the way of sailing vessel A.
The upwind sailing vessel must keep out of the way of the downwind sailing vessel.
The ship is to berth alongside a quay in calm conditions of no wind or current. The ship has a signle fixed pitch right handed propeller. Which angle of approach would be considered the most favourable?
The decision should be left to the pilot who is in charge of the manoeuvre.
What are we seeing here?
A sailing vessel of less than 10 metres in length, displaying the mandatory combined lantern in lieu of sailing lights, seen head-on.
A sailing vessel, seen from astern, where the edges of her sidelights are both visible.
A sailing vessel less than 20 metres in length, displaying the optional combined lantern in lieu of standard sailing lights, seen head-on.
A sailing vessel, at anchor.
When plotting a position, where should the Officer of the Watch select as the ships position, when three gyro compass bearings intercept as a triangle (Cocked Hat) and not as a single point?
At the point furthest away from any danger.
At the point nearest the course line drawn on the chart.
At the point nearest to the danger, if any.
At the centre of the triangle.
Which type of vessel suffers from the greatest squat effects?
Vessel with a low Block Coefficient.
Vessel with a small length to beam ratio.
Vessel with a high Block Coefficient.
Vessel with a large length to beam ratio.
What would be the stopping distance of a VLCC when proceeding at 8 knots in deep water and the engines are put “Full Astern”?
Varies, but can be determined from trial data.
What is the description for a sidelight, as shown in rule 21 of the International Regulations for Preventing Collisions at Sea?
A red, green or yellow lantern, showing an unbroken light over an arc of 112,5°.
A green light on the starboard side and red light on the port side, showing an unbroken light over an arc of 135°, from right ahead to 22,5° abaft the beam on the respective side.
A green light on the starboard side and red light on the port side, showing an unbroken light over an arc of 112,5°, from right ahead to 22,5° abaft the beam on the respective side.
A red light or a green light, with a minimum range, in a vessel of 50 metres or more, of 3 miles. In a vessel of 10 metres.
The vessel is steaming off the coast when the engine room informs the bridge it must stop engines immediately. Shortly afterwards they informed the bridge they would need a least three hours to fix it. Which of the following actions would be the most suitable taken by the bridge?
Display the NUC signal and keep a good lookout.
Display the NUC signal, maintain the watch and ask the Engine room to be a quick as possible.
Display the NUC signal, maintain the watch and wait for further developments.
Display the NUC signal, maintain the watch and determine how the ship is drifting and the probable position after 3 hours.
You are on a power-driven vessel underway in open water. You sight these lights on the port bow, on a steady bearing. The distance is closing. What are you looking at and what action will you take in compliance with the International Regulations for Preventing Collision at Sea.
This is a power-driven vessel engaged in towing, less than 50 metres in length, length of tow under 200 metres and the tow, both being restricted in their ability to manoeuvre, seen from the starboard side. Under rule 18, I am required to keep clear and will take appropriate avoiding action.
This is a power-driven vessel, more than 50 metres in length or less than 50 metres in length and showing a second masthead light, restricted in her ability to manoeuvre. The sidelight of a second vessel can be seen beyond her. Under rule 18, I am obliged to keep clear of the first vessel and will therefore take appropriate avoiding action.
This is a power-driven vessel engaged in towing, more than 50 metres in length or less than 50 metres in length and showing a second masthead light, length of tow 200 metres or more, not under command. I will keep clear under rule 27.
What letter is represented by this flag and what is it’s meaning when displayed by a vessel in port?
P – All persons should report on board as the vessel is about to proceed to sea.
S – I am operating astern propulsion.
W – All persons should report onboard as the vessel is about to proceed to sea.
With a pilot ladder, the lowest spreader shall be the 5th step from the bottom. At what interval should there be further spreaders upwards on the ladder?
It does not matter where the spreaders are fitted.
At intervals not exceeding 12 steps.
At intervals not exceeding 15 steps.
At intervals not exceeding 9 steps.
What is the correct understanding of the term “Block Coefficient” as applied to a ship?
The coefficient of a Block and Tackle.
The ratio of the waterplane shape of the ship to a rectangle of the same extreme dimensions.
The comparisons of the underwater shape of the ship, to a rectangular block of the same extreme dimensions.
The restriction of a valve in a pipe to the flow of fluid through that pipe.
The ship has a single fixed pitch right-handed propeller and is going astern as illustrated. What is the most likely way the ship will react in these circumstances?
The stern will “back” into the wind and the ship’s heading will swing to starboard.
The stern will fall off to starboard, making the heading swing to port.
The bow will “seek” the wind and the ship will swing to port.
The ship will go straight astern and the heading will remain approximately the same.
What would be considered the most favourable heading of a ship when launching a lifeboat?
The ship should lie stopped in the water with the weather on the opposite side to the boat to be launched.
The ship should steer about 100° of the prevailing weather and sea with the boat to be launched on the leeside.
The ship should steer with the prevailing weather and sea on the beam and the boat to be launch on the leeside.
The ship should steer about 30° off the prevailing weather and sea with the boat to be launch on the leeside.
The ship is required to be stopped in the water as quickly as possible, but without major changes to the ship’s heading. What is the most effective method to achieve this?
Put the engine full astern and keep the rudder amidships.
The use of the rudder hard over both sides combined with reducing engine power, a method known as “high frequency rudder cycling”.
Make a complete turn while reducing the engine power.
Make a zig zag manoeuvre while reducing the engine power.
A ship is being overtaken by another ship while proceeding along a river. What should be the required procedure?
The overtaking vessel should request permission to overtake from the Port Control VTS.
The overtaking vessel can overtake but must allow sufficient space to reduce the interaction between the two vessels.
The overtaking vessel should request permission from the other ship by sounding two prolonged blasts followed by two short blasts on the whistle or by direct VHF contact.
There should be no overtaking in these confined waters.
How can a new officer, just boarding a ship, ensure that he knows the location and operation of all navigational and safety equipment and take account of the operating limitations of such equipment?
By following the standard company Induction procedures for a bridge watchkeeping officer.
By using the equipment on regular watchkeeping duties.
The certificate of competency will ensure the officer has suitable competence in operating the bridge equipment.
By asking other officers and practicing with the use of the equipment.
Which of the following answers correctly specify the following most common rudders? a) UNBALANCED, b) BALANCED, c) SEMI-BALANCED and d) UNDERHUNG BALANCED. i. e. The number in the picture is related to the letter adjacent to the name of the rudder.
1 = d, 2 = a, 3 = b and 4 = c.
1 = b, 2 = c, 3 = d and 4 = a.
1 = a, 2 = b, 3 = c and 4 = d.
1 = c, 2 = d, 3 = a and 4 = b.
Who is ultimately responsible for approving the voyage plan?
The Officer of the Watch (OOW) on duty.
The Second Officer as the official Navigation Officer.
The ship owner will provide overall parameters within which the ship must follow.
Which of the following hull shapes would normally provide a directionally stable ship?
A long ship with a narrow beam.
A short ship with a wide beam.
A short ship with a narrow beam.
A long ship with a wide beam.
What is the depth of an iceberg below the surface of the sea?
The draught of an iceberg is normally about 3/4 of its total depth.
The draught of an iceberg varies with the type of berg and its age.
The depth of an iceberg below the surface is always about one sixth of its total depth.
The draught of an iceberg is about the same as the visible part of the iceberg above the water.
The tug has been released and is all clear. As officer in charge of that operation, should this be reported and to whom?
Reported all clear to the Bridge.
Report all clear to the tug.
No need for reporting as the order was given from the bridge.
Report all clear to the Engine Room.
Two mooring lines are pretensioned equally and have the same length, same breaking strength and same directional load. However, one is made of wire (with a full load elastic elongation of about 1,5 % of its length) and the other made of nylon (with a full load elongation of about 30 % of its length). If a gust of wind increases the load on the lines, how will it be shared?
The wire and rope will share the load equally.
Wire takes 45 % of the extra load. Rope takes 55 % of the extra load.
Wire takes 55 % of the extra load. Rope takes 45 % of the extra load.
Wire takes 95 % of the extra load. Rope takes 5 % of the extra load..
The positions of the ship provided by the GPS receiver should always be verified by other means. Which of the following suggested methods would be the most accurate?
Bearing and distance from a navigational buoy.
Radar bearings of three distinctive shore objects.
Radar ranges of three distinctive shore objects.
A DR updated position from the last reliable one.
Which option best completes the following statement? An operator using ECDIS, will notice an out of position navigation buoy because:
There will be a flashing alarm on ECDIS showing which one is out.
A local port authority would send an automatic signal to ECDIS.
The radar return and ENC buoy symbol will not coincide.
It is coloured orange on an ECDIS display.
What is the weather associated with being in the centre of an Anticyclone (a region of High Pressure)?
Strong winds and heavy rain.
Persistent rain and very humid weather.
Strong winds but with very little rain.
Light winds and fair weather, sometimes fog.
What can be used to reduce the effect of the state of sea-water?
Is the location of the Compass Binnacle critical?
Yes, it should be on the fore and aft centreline of the ship.
Yes, it should be sited on a non-metallic base if possible.
Yes, it should be away from all electrical power cables.
Yes, for the reasons stated in all of the suggested answers.
In a canal without water flow, if a vessel was approaching a bank at an angle, what would be the probable effect on it?
The vessel’s stern is pushed away from the bank.
The vessel’s bow is attracted by the bank.
The vessel’s bow is pushed away from the bank.
The whole vessel would continue straight towards the bank and would require a large helm order to avoid going aground.
If the radar is set onto the Relative Motion Display, what would an echo of a target with no trail indicate? Note this the trail of the echo and not a vector.
The target is stopped and making no way through the water.
The target is on the same course and speed as own ship.
The target is on a constant bearing and getting closer to own ship.
The target is on a collision course with own ship.
When splicing an eye on a mooring wire (using the recommended 5 full tucks and 2 half tucks) the effective breaking strength of the wire may be affected by the splice. What would be the anticipated change in the breaking strength of the wire?
A reduction in strength of 1 % to 5 %.
A reduction in strength of 10 % to 15 %.
A reduction in strength of 30 % to 40 %.
No reduction in strength.
This vessel is sighted ahead and slightly to port. What is her situation? What will you do?
This is a vessel engaged in fishing vessel, with her nets fast on a obstruction. I will keep out of the way by rule 18 of the International Collision Regulations.
This vessel is aground. I will navigate with extreme caution given the nature of the hazard.
This is a vessel not under command at anchor.
This is a vessel aground. She appears to have been headed to starboard of my track and I will therefore alter course to port, passing under her stern.
What could be the reason for the magnetic compass to swing through large angles when the ship is rolling in a seaway?
The error due to deviation is large for that ships heading.
The Coefficient B determined by the Compass Corrector at the last dry-dock was not correctly calculated.
The heeling error magnets are upside down and/or not in the correct position.
The induced magnetism from the earth’s magnetic field is very strong in that area.
When navigating using the GPS, how does the GPS display indicate when the accuracy of the displayed position is reduced?
A large HDOP value is displayed on the screen.
A large “Correction Factor” number is displayed on the screen.
The GPS display flashes and sounds an alarm.
The GPS display is always very accurate and does not give any indication of lack of accuracy.
Where can the size of the Magnetic Compass Error be found?
By taking the error from the Deviation Table on the bridge.
By taking a transit bearing of two fixed geographical positions and comparing it with the bearing of the same points on the chart.
On the chart in the centre of the compass rose or by reference to the Variation chart, taking into account the annual changes.
By reference to the last entry in the Compass Error Log Book.
Which of the four calculations illustrated is the correct one to determine the latitude of the observer when the sun is on the meridian?
Calculation 3 is correct.
Calculation 2 is correct.
Calculation 1 is correct.
Calculation 4 is correct.
Who is responsible for the number and the position of any tugs to be used during a mooring operation?
The Master, with consideration of the advice of the pilot.
The Pilot is fully responsible for the number and use of tugs within the port area.
It will be only the wind speed that will determine the required number of tugs and how they are used.
The Port Authority will dictate the tug requirements and their use within the port limits.
Which is the “CENTRE LINE”, in the figure?
The Fore and aft Centreline is indicated by D, in the figure.
The Fore and aft Centreline is indicated by B, in the figure.
The Fore and aft Centreline is indicated by C, in the figure.
The Fore and aft Centreline is indicated by A, in the figure.
Once a ship (equipped with self-stowing auto-tension winches) is moored alongside a loading or discharging berth, how is it recommended that the winches are set?
All mooring winches be left in “auto-tension” mode.
All winches to be left with the manual brake on and out of gear.
The “breastline” and “headline” winches be left in the auto-tension mode and spring winches with manual brake on.
The “spring” winches be left in the auto-tension mode and all other winches with the manual brake on.
The ship is drifting in the open sea with a temporary engine breakdown. The ship is equipped with GPS navigation equipment. What should the bridge Officer of the Watch do in this situation?
Plot the direction and rate of drift and predict the ships position for the period while the ship is “Not Under Command”.
Keep a good lookout for other ships.
All of the possible answers.
Display the “Not under Command” signal and switch off the normal steaming lights.
The lights here show those that must be exhibited by a vessel engaged in towing, as per rule 24 of the International Collision Regulations. But how long is the tow behind this vessel?
It is less than 200 metres.
It is more than 50 metres but less than 200 metres.
What would be the effects of a ship passing into shallow water?
The vessel has a tendency to swing to port with a single fixed-pitch right-hand turning propeller.
There is no noticeable difference in performance of the ship.
The speed is not affected, but more rudder is required to steer the ship.
The ship is less responsive to both rudder and propeller.
The following vessels are all required to make the same sound signal when in or near an area of restricted visibility: a vessel not under command; a vessel restricted in her ability to manoeuvre; a vessel constrained by her draught/a sailing vessel; a vessel engaged in fishing; a vessel engaged in towing or pushing another vessel. What is that signal?
Two prolonged blasts, followed by one short blast, at intervals of not more than 2 minutes.
One prolonged blast, followed by two short blasts, at intervals of not more than 1 minute.
One prolonged blast at intervals at not more than 2 minutes.
One prolonged blast, followed by two short blasts, at intervals of not more than 2 minutes.
What are the required data inputs into most gyro compasses to reduce any possible compass error?
All of the data in the suggested answers.
Maximum helm angle and rolling period.
The gyro compass can suffer from a compass error and may need to be allowed for, when steering a course in a dangerous navigational area. What is the probable cause of the error?
An uncorrected course and speed error.
Fluctuations in the electrical supply to the compass.
What are the additional duties required by the Officer of the Watch when navigating in fog?
Sound fog signal, effective radar watch reporting ship movements to Master and keep a good lookout for ships and fog signals.
All of the suggested answers.
Sound fog signal, plot positions and keep a good lookout.
When navigating in fog the Master will take over the watch and the Officer of the Watch should follow all of his instructions.
Rule 12 of the International Collision Regulations prescribes the action to be taken by a sailing vessel when meeting another sailing vessel. This depends on the direction of the wind relative to each vessel. In the situation shown here, which sailing vessel (A or B) must keep out of the way of the other?
The upwind sailing vessel must keep out of the way of the downwind sailing vessel.
Sailing vessel B must keep out of the way of sailing vessel A.
Both sailing vessels are required to take avoiding action.
Sailing vessel A must keep out of the way of sailing vessel B.
The ship’s rudder is full over when the ship’s engines are full ahead. Will the turning effect (lift force) of the rudder be changed when the engine is stopped?
Yes, the lift or turning force will be reduced to about 50 % of the original lift force when the engines are stopped.
Yes, the lift force will be dramatically reduced when the engines are stopped.
No, the lift force is unaffected by the speed of the propeller.
No, the turning force applied by the rudder will be maintained within about 90 % of the lift force when going full ahead.
A ship normally turns (swings) around a point which is not the centre of gravity. What is this point normally called?
Which of the following answers most suitably cover the standard duties of the bridge Officer of the Watch when the ship is at anchorage?
Display anchor signal, check the ships position and keep a good lookout.
Display anchor signal and keep a good lookout of other ships in the area.
Display the anchor signal, patrol the ship frequency and check the anchor chain for dragging.
Display the anchor signal and ensure the ship swings the same way at each change of tide.
You are in an area of restricted visibility and hear this signal. It is repeated at 2 minutes intervals. What does it indicate?
That there is another vessel nearby, that she is underway, but stopped and making no way through the water.
That there is another vessel nearby, but that she is at anchor.
That there are two more vessels nearby.
That there is another vessel in the vicinity and that she has just altered course to port.
Visual signals are used by aircraft in search and rescue operations to direct ships towards a casualty. The signals shown here are part of a sequence. What does it indicate?
The assistance of your vessel is no longer required.
The casualty is sighted and will require medical assistance.
The aircraft is short on fuel and is returning to base.
The aircraft is directing a vessel towards the casualty.
Why should Ground Stabilised True Motion display mode be avoided when using the ARPA for anti-collision purposes?
The Relative Motion display and relative vectors is the only display to use for anti-collision purposes.
True motion does not provide the collision risk of other ships.
The true vector can never give an indication of collision risk with another ship.
The collision regulations are based on ship courses through the water.
The rudder is in the hard over position with the propeller stopped and the ship turning slowly. On a ship with a single fixed pitch right handed propeller and no thrusters, what can be done to make the ship increase the speed of turn without significantly increasing the forward speed of the ship?
Give dead slow ahead on the engines and leave the rudder in the hard over position.
Give the engines a short kick ahead.
Give half astern on the engines as this will increase the rate of turn.
Give full astern on the engines until ship has stopped and then full ahead on the engines with rudder hard over.
You are approaching the port entrance. What do these lights mean?
Vessels may proceed – one-way traffic.
Vessels may proceed – two-way traffic.
A vessel may proceed only when she has received specific orders to do so.
A vessel may proceed only when she has received specific orders to do so, except that vessels which can safely navigate outside the main channel need not comply with this message.
What can be a cause of error observed on a gyro compass reading?
Fluctuations in the magnetism around the compass.
Incorrectly set heading and speed values.
Incorrectly set latitude and speed values.
Large values of variation caused by the gyro pole.
What does this signal hoist mean?
I require medical assistance.
Do you require assistance?
I require immediate assistance.
What is the depth of an iceberg below the surface of the sea?
The depth of an iceberg below the surface is always about one sixth of its total depth.
The draught of an iceberg is about the same as the visible part of the iceberg above the water.
The draught of an iceberg varies with the type of berg and its age.
The draught of an iceberg is normally about 3/4 of its total depth.