Tug Boats

The name Tug Boats gives a fair idea about the size and task of the vessel being discussed. These are relatively smaller but very powerful for their size. These are primarily used to tug or pull vessels that cannot move by themselves like disabled ships, oil platforms and barges or those that should not move like a big or loaded ship in a narrow canal or a crowded harbor. In addition to these, tug boats are also used as ice breakers or salvage boats and as they are built with fire fighting guns and monitors, they assist in the fire fighting duties especially at harbors and when required even at sea.

 With the developments in the shipping industry the ships began to grow larger than they ever were in the history. It is easy to maneuver them at sea but becomes exceedingly difficult in narrow sea strips and harbors because they can move forward and backwards with ease but usually have problems with sideways movement. This is when the need of tug boats was felt and thus these vessels were introduced to help the larger ships navigate the narrow waters. This came to be known as tug assist and thus the name of the boats.

Most of these boats can also venture out in the ocean but some of them are not that strong like the river tugs. The river tugs are tow boats designed to help out in the rivers and canals. They have a hull design that makes it quite dangerous for these boats to venture into open Ocean.
The tug boats were one of the first to have a steam propulsion engine which in today’s time has been replaced by the diesel engine. An average tug boat has an engine of 680-3400 hp (500-2500 kW) but boats which are larger and venture out into deep waters have engines with a power close to 27200 hp (20000 kW) and a power : tonnage ratio ranging between 2.20-4.50 for large tugs and 4.0-9.5 for harbor tugs.

 These are extremely high ratio especially considering the ratio of the cargo ships or general ships that varies between 0.35-1.20. Such boats usually have engines which are quite similar to the ones used in railway locomotives but with a notable difference that they mechanically drive the propeller instead of converting the output to electric motor supply.

Since the maneuverability of a tug boat has been one of its assets, all the engine developments over the years have focused on the aspect of improving on it without compromising on the strength and power of the vessel. Thus the transition from the paddle wheels to the propellers. The tug boats have been the topic of many literary works especially children’s works like cartoons. They have provided inspirations to many to create characters that have long lived in the memory of the people and attracted many to study them. The real life boats and their crew are as resolute and lovable as their counterparts in fiction and the cartoons. Looking back, one can easily say that a tug boat is more than just a boat, and an important jigsaw piece in the historical scheme of things about everything related to sea.

Duties of Chief Officer

The operation of a ship is a result of the excellent team work of deck and engine department. One cannot run the ship with only engineers on board or for that matter with only deck officers. While the engine department ensures safe running of the ship’s machinery, the deck department is an organizational unit in which, deck officers performs navigational and other important duties directly related to the efficient working of the ship, apart from those involved with the engine room.

 One of the most important ranks among deck officers is that of a Chief Officer, the head of deck department of the ship. He is one of the four management level officers on the ship who report directly to the captain and is second in command after the master of the ship.

Important duties of a ship’s Chief Engineer includes
1. Chief Officer is responsible for performing vessel navigation watch duties.
2. He is responsible for the entire cargo operation in ports which includes loading, unloading, and cargo planning.
3. He is the in-charge for maintenance of cargo gears and cargo carried on board ship.
4. One of the critical tasks performed by chief officer is the accountability of the stability of the ship.
5. He is responsible for maintenance of ship’s hull and accommodation.

6. All the life saving and fire fighting appliances of the vessel comes under the responsibility of chief officer.
7. His duties includes administration task of scheduling and distributing work to deck crew.
8. He has to build up the co-ordination with other departments and take part in conflict resolution.
9. He is responsible for garbage management for the deck and accommodation part of the ship.
10. He is in charge of the ballast and de-ballasting operation done on board.
11. He has to make sure all the crew members are complying with latest rules of MARPOL, SOLAS and STCW.
12.  ISPS code is another responsibility that the chief officer has to look over.
13.  Trainings in all the above regulations and conventions are to be carried out by chief officer as per company policy.
14.  To look after supply, overtime, cost control records, purchase order, requisition, and other paper work on behalf of shore management.
15.  He also acts as SSO- ship security officer, responsible for the security of the ship both in port and at sea.
16.  He is the overall safety in charge for the deck crew.
17.  He is responsible for the welfare of the crew on board ship.
One cannot think about operating a ship without considering the position of chief engineer. He is a key position on the ship, one who assists master and shore management and helps in training crew and juniors.

Electronic Chart Display and Information System (ECDIS)

The Electronic Chart Display and Information System (ECDIS) is a development in the navigational chart system used in naval vessels and ships. With the use of the electronic chart system, it has become easier for a ship’s navigating crew to pinpoint locations, and attaining directions are easier than before.

The ECDIS utilises the feature of the Global Positioning System (GPS) to successfully pinpoint the navigational points. Because the GPS is a highly reliable system, the utility and the reliability of the ECDIS as an electronic chart system can never be doubted. It also has to be noted that the ECDIS adheres to the stipulations set by the International Maritime Organisation. This factor also adds to the trustworthiness of the electronic chart system.

In addition to the GPS for pinpointing routes, the ECDIS also employs the systems of AIS and Radar in order to facilitate better navigational application. The navigational routes are displayed incorporating of a system known as Electronic Navigational Charts.
Types of ECDIS
There are two different types of ECDIS and both are used in different sectors of marine areas, in spite of the technology involved being the same.

• Vector ECDIS: The vector variation of the electronic chart system is used mainly by government naval vessels than commercial ones. The Vector ECDIS adheres to the norms set up by the International Hydrographic Organisation and is well advanced in the sense that, it can be pre-programmed to indicate any threat to a naval vessel’s position in case other ships and naval vessels are also in a similar location in the water.

• Raster ECDIS: These are a more traditional variant of the ECDIS. In these, navigational charts that are charted out in paper are scanned and converted into the Electronic Chart System format. Because of such a conversion, it so happens that if one wants to zoom in or zoom out a particular navigational route, the process is quite easy and feasible. For the purpose of display the navigational charts in this particular electronic chart system, the technology of Raster Chart Display System (RCDS) is used in case there is an absence of the Electronic Navigational Charts.

The concept of ECDIS is something that is gaining more and more popularity in today’s times. This is mainly because the concept has been officially allowed to be incorporated in the naval vessels and ships. By adopting this method of marking and charting navigational routes, it has become easier to avoid any unwanted accidents as this electronic chart system uses modern technology rather than human aid.
The ECDIS as an electronic Chart System is something that allows shipping companies and ship owners a lot of mental freedom when it comes to the safety of the vessel in the water. Because of this technology, it can be said that the aspect of navigation has become faster, simpler and sleeker.

5 International Mobile SIM Cards for Seafarers

Seafarers are frequent travelers who love their mobile phones – the vital tool which helps them to connect to their family anytime, anywhere! We asked a couple of our seafarer friends as to what is the one thing they never forget when they leave for sailing, and “mobile phone” is the answer we received from every single one. One of the seafarers answered, “To be honest, mobile phone is one equipment which helps to restore our sanity on board ships when all other equipment are giving us a tough time.” We can’t agree more!


So the question is – Which mobile SIM cards do seafarers use? Do they buy a new SIM card at each port or Do they activate international roaming on the number they use on land (Which is outrageously expensive!) or buy a global sim card?.
We received a number of different answers. Some said that they buy SIM cards at the ports, which are to be frequently visited by their ships; whereas some prefer to buy mobile cards in those ports wherein the calling rates are the lowest. Some uber-social seafarer even activate international roaming on their local numbers or take a Global sim card which will allow them to have the same phone number around the world. However, they mainly use such services to receive text messages (which is usually free!) and to make urgent calls.
Considering the importance of mobile SIM cards/ international calling cards that seafarers have in their lives, we decided to make a list of the most commonly used global sim cards (those which will allow them to have the same number wherever they go).
Note- There are hundreds of international SIM cards providing companies in the world and it would be difficult to accomodate all of them in this article. Thus, we are starting with the list of cards that are used by Indian Seafarers or those that provide their services in India. This is NOT a sponsored article! 

Though we have personally used a few of these cards, we haven’t tried all and thus cannot comment on them. Kindly use at your own risk as some of our seafarer friends have complained of unimaginable bills, especially on international roaming.
1. iVitta – The iVitta Sim Cards are specially crafted for seafarers, considering the communication issues they face. They are available at several seafarer centers around the world and “top-up” can be done online from anywhere.
2. Reliance World Sim  - The Reliance World Sim card claims to offer international roaming services in more than 160 countries with free incoming calls in over 30 countries. The service providers assure of 70% less on the bill than what you would pay by activating roaming services on your own number. Click here to know more.
3. One Sim Card - One Sim Card is an International SIM card provider which offers international sim card roaming in more than 190 countries at affordable rates. It offers free incoming calls in more than 150 countries and free text messages worldwide.
4. Matrix  - An international SIM card provider which offers both post paid and pre paid SIM cards. These travelling cards also come with a data package offer and can be recharged online from anywhere in the world.
5. Airtel World Calling Card  - Airtel world calling card offers international roaming services in more than 95 countries. The card doesn’t require any additional deposits or processing fee.
There are several other companies which offer international sim cards for seafarers/ frequent travelers in India. It is extremely important to go through the terms and conditions, call rates and other important information before buying an international sim card from any service provider.

Bridge Navigational Watch and Alarm system

 Navigating a giant vessel is not at all an easy job and when it comes to a situation of emergency, wherein the navigational officer has to make some quick decisions, the safety of the entire ship and its crew depends on that officer. This is when automated systems are extremely useful. BNWAS is one type of automated system used on ships.


What is BNWAS?
Bridge Navigational Watch & Alarm System – BNWAS is a monitoring and Alarm system which notify other navigational officers or master of the ship if the officer on watch (OOW) does not responds or he/she is incapable of  performing the watch duties efficiently which can lead to maritime accidents.


Why Ship Need BNWAS?
There have been many incidents in the past wherein ship has collided or grounded due to wrong decision or inefficiency in taking decision at the correct time. If during an emergency situation navigational officer is not capable to handle that situation it can lead to devastating scenarios. To avoid this BNWAS is installed on bridge which acts similar to a dead man alarm in the engine room.

A series of alert and alarm is first sounded by BNWAS in the Navigation Bridge to alert officer in watch. If there is no response to the series of alarms, then BNWAS will alert other Deck officers, which may include Master of the ship, so that someone can come out on bridge and handle the situation and tackle the problem.

Regulations for BNWAS
SOLAS chapter V regulation 19 states that all passenger ship and cargo ships 150 GT and above must install BNWAS on or after 1^st July 2011 with some waver in terms of installation period for old vessels. The system must be approved by classification societies and should be easy to operate.
BNWAS must be operational when ship is heading on a voyage unless instructed by the master of the ship.

The shipping industry has incurred mammoth losses in past few years due to incidences of collision and grounding. The primary reasons of such unfortunate events have been termed as sheer negligence and failure to comply with effective bridge watch keeping rules.

The new resolution passed by IMO focuses on the importance of using BNWAS – Bridge Navigational Watch and Alarm system to prevent accidents as a result of watch keeping flaws.

Chief Officer Abhishek Bhanawat explains the importance of BNWAS by describing two unfortunate accidents which were caused as a result of sheer negligence on the part of OOW to carry out their duties properly.
Incident 1
While transiting a river while approaching the Port of Balikpapan, Indonesia, an Italian flagged vessel was grounded on a reef. The reason for this incident, upon investigation, was revealed sheer negligence on the part of Officer on Watch (OOW).
The ship’s passage plan indicated the course as a critical one and the course line was laid so as to clear the reef by 5 cables. The OOW was distracted by the phone signal and did not check the position of the vessel frequently. He even altered the course slightly to get a better signal strength, which brought him closure to the reef.
Eventually, the vessel was grounded, amounting to salvage and heavy fine to the owners. Luckily none of the underwater compartments got damaged for the vessel was carrying around 30,000 MT of fuel oil cargo. The root cause found was failure to follow the passage plan and overlooking of the guidelines for effective watch keeping.
Incident 2
In another incident, which occurred in Singapore Strait few years back, a container vessel collided with an oil tanker. The bow of the container struck the mid ship compartment of the VLCC. There was loss of life, damage to property and environmental pollution as well. Investigations revealed that the OOW on board the container vessel was working on the bridge computer while the vessel was transiting Singapore Strait. By the time he saw the VLCC crossing from Port to Starboard they were in a close quarter situation. Avoiding action taken by the OOW was not sufficient and timely to avoid the catastrophe. Underlying cause again was found to be lack of effective watch keeping.
Due to alarming increase of activities similar to the above mentioned ones, the International Maritime Organization (IMO) has come up with a resolution A.694(17) associated with IEC 60945.This resolution focuses on BNWAS –  Bridge  Navigational Watch alarm system. With basic principle of monitoring bridge activity and disability of duty officer, the system can consequentially function as a preventer of marine accidents.
With the help of a series of alarms and indicators this system is able to determine if a bridge watch keeping officer is disable to execute his  watch keeping  duties and subsequently alert Master or another qualified OOW. Furthermore it can be an aid to call assistance if required by the OOW.

A mandatory requirement as per  Ch. V of  The International Convention for Safety of Life at Sea (SOLAS), BNWAS  or  the Dead man alarm system for bridge , is mandatory for all existing cargo ships >3000GRT and not later than the first survey after  1^ST July 2012.
The operational requirements for a BNWAS emphasize on alerting the ship’s master and other qualified watch keeping officers in an event of disability or negligence of OOW.
To elaborate further BNWAS has a three stage alarm system. Once operational, the BNWAS within 12 minutes will initiate a visual indication on the bridge. If not reset, the BNWAS will sound a 1st stage audible alarm, in the bridge, 15 seconds after the visual indication was initialized.
If the alarm is still not acknowledged within 15 seconds of the first stage alarm, the BNWAS will sound a second stage remote audible alarm in Master’s cabin or other qualified OOW’s location. If the second stage alarm is not acknowledged within 90 seconds, it will sound a third stage alarm at the location of further crew members who are capable of taking action. If after any stage the alarm is reset, it will again activate after 12 minutes of last indication. Such great features make BNWAS inevitable part of bridge watch keeping and prove to be a great aid in mitigating the risks to ship owners.

Ships Squat

Motion of a ship on water is a result of several hydro dynamics in play all at same time. Of the several phenomena that occur at once, ship squat effect is a fairly important one. On several occasions, ships have run into extreme situations because of this particular effect. For all mariners and ship lovers, understanding what is ship squat and how it affects the motion of a ship is fairly important.

What is ship squat effect?
To understand this better, consider image of a ship moving through waters. As the ship’s hull cuts through the water’s surface, a volume of water is shoved aside. This water is actually replaced to sides and underside of the ship.


This creates a region of low pressure, causing the ship to dip vertically at points of low pressure. The vertical dip in the ship caused due to low pressure is actually the ship squat effect. This dip is proportional to the speed of the ship.
The major effects of such low pressure conditions are especially felt in shallow water, even more so if the ship is going at a high speed. That is where the relation between ship’s speed and the squat effect comes handy. Altering the speed can greatly help maneuver through the shallow waters easily. Cutting the speed down by half would approximately lower the squat effect by a factor of four.
Why is ship squat important?
A ship’s squat is one of the more important things that help in ensuring a ship’s safety through water. Vessel squat is a combined outcome of ship’s dimensions, weight, water depth, wind draft and several other factors that come into play while a ship is in motion.
Knowing a ship’s squat becomes important then as its loading capacity, speed, its seaworthiness through particular routes would all be affected by its squat value. As mentioned above, vessel squat is proportional to ships’ speed. So it becomes important information for a ship’s pilot that increasing his ship’s speed by a certain factor, he would also be increasing the ship’s squat. Or while loading a ship, say for a 100,000 tons dwt tanker, a load of extra 30 cm could increase the ship squat by 3%.

These become crucial pieces if information to ensure a ship reaches destination safely. Besides, it is always sad when a ship runs aground or is rendered out of service, for any reasons. Certain factors like ship’s speed and load weight can be checked to prevent such incidents. Hence, knowledge of vessel squat could ensure a ship wouldn’t have to face such avoidable circumstances.
Is ship squat good or bad?
There is no straight answer to this question. In certain situations, while traveling in shallow waters, ships have been grounded due to ship squat effect. Grounding of QE2 would be a perfectly good example of that, where the ship ran aground despite of having enough room for its passage. That happened due to additional vertical dip experienced by ship, causing it to brush off against a rock that would otherwise have caused no harm.
Since 1987, more than 113 ships have run aground chiefly because of the squat ships had to experience. On the flipside, this very property has been used in certain occasions to help ships pass through regions otherwise considered unfavorable. Travel of largest ship of the world, Oasis of Sea, through Great Belt Bridge would be a perfectly good example of that.
It can be said now that the total squat ship has to experience plays role in its overall integrity, which is for sure. However, it becomes a matter of captain’s discretion especially upon entering shallow waters that can prevent things from going bad.

Mastering Ship’s Navigation

A navigational or deck officer has to be extremely careful while steering a vessel from its course no matter where the ship is – at mid sea, crossing channel, or entering/ leaving a port.

The team at the bridge should be efficient enough to sail the ship in all kinds of waters and weather.
One of the natural factors about which every navigator should be very careful while steering a ship is – the wind.

Vessels such as Container and Ro-Ro ships have large freeboard and are thus more affected by winds. This exposed area of the ship is also known as windage area as the effect of wind is more prominent over it.
The wind effect on the same ship will be different at different places, depending upon the draught condition of the ship.
A wind with force of 3-4 on the Beaufort scale will have similar effect in light condition as with wind force of 7-8 when the ship is down to her marks.
When ship is at slow speeds during maneuvering or near to the coast, wind direction is easy to find; but this is not the case when out at high sea. The direction of the wind perceived when standing on deck is its relative direction. This is the resultant of the true direction of the wind and the course steered by the ship.

It is very important for the ship’s navigator to steer the ship considering the wind effects so that ship can be steered efficiently without any difficulty. Following are the techniques a navigator must master related to wind effects.
Ship underway with wind from right astern
When the wind is blowing from the right astern, steering the ship becomes easy; however, in the case of head wind, the stern part of the ship has the tendency to pay off on either side. This is a difficult situation to tackle and getting the ship back on course is no piece of cake.
Such effect is more often seen on ships where the accommodation area is at the aft region. Moreover, the wind in such case has no braking effect.
Note: Given a choice between head wind & wind from right astern, the head wind is preferred for berthing.
Ship underway with wind from abeam
When the ship is underway with the wind flowing from abeam, the steering of the ship is not affected. However, depending on the strength of the wind, the ship drifts sideways due to leeway and this has to be accounted for while handling the ship.
Ship underway with wind on the bow
Here again in lighter conditions, the effect on the ship’s stem is larger and this tends the ship’s head to swing away from the wind (leeward). This requires the weather helm (helm on the side of the wind) to be steered continuously.
Ship underway with wind on quarter
When the wind is pushing the ship’s stern away to leeward, the stern tends to swing towards the leeward. The ship is therefore steered towards the wind and the ship is required to be given a lee helm.
Vessel under sternway
When the ship is going astern, it rarely goes at a great speed. When going astern most ships also tend to swing to the starboard. The effect of the wind is therefore a little more complex.
In ballast condition where the wind catches the bow, which it often does, the stern is pulled into the wind. This effect is quite definite & rapid.
Note – This effect must be remembered while maneuvering for anchoring, berthing etc.
All ships turn around a pivoting point. This point is an imaginary reference and is fixed from observations of the ship turning around. It is known that when going astern the pivoting point moves aft.
Conclusion
Navigators can use the wind:
1.    As a good brake
2.   As a device for making a tight turn.
3.   To maneuver comparatively easily as long as the wind remains about    two to three points on the bow


The effects of ocean current
Ocean currents play a very important role in ensuring the stability of the ship.
The effect of currents therefore must also be considered when handling ships in waters.

Effects of current are important especially when the ship is under the effect of on shore winds, near off shore platforms, while maneuvering in narrow channels  and open seas, or in inland waters or harbors. When the ship is in harbors or inland waters and the current is at constant strength and direction, the ship’s handling becomes considerably easier.
Such conditions exist only in comparatively narrow channels of the rivers.
However, navigational officers should take into account different current streams that can exist over a small area, within which the vessel has to maneuver.
The main different between currents and winds is that currents affect the ship in definite and predictable ways, unlike the wind does.
Even in open waters, when the ship is approaching a rig or a mooring buoy, due allowance should be made for the effect of the current for a safer maneuver.
Current from ship’s ahead will reduce the ship’s speed over ground, improve ships response to the rudder, and also give more time to assess and correct developing situations.

Shallow Water Effects on Ships – Ship Squat
When a ship proceeds through water, it pushes the water ahead. This volume of water returns down the sides and under the bottom of the ship.  The streamlines of return flow are speeded up under the ship, causing a drop in the pressure and resulting in the ship dropping vertically in the water.
When the ship drops vertically in the water, it trims both forward and aft.  This overall decrease in the static under keel clearance, both forward and aft, is called Ship’s Squat. Learn more about Ship’s Squat here.

If the ship moves forward at a greater speed in shallow water, where the keel clearance is 1.0 to 1.5 metres, then there are high chances of grounding  at the bow or stern due to excessive squat.

What are the factors that govern Ship’s Squat?
The main factor on which the ship’s squat depends is the ship’s speed. Squat varies approximately with the speed squared.
The blockage factor “S” is another factor to be considered while understanding ship squat.  The blockage factor is defined as the immersed cross-section of the ship’s mid-ship section divided by the cross-section of water within the canal or river.
The blockage factor ranges from about 8.25b for super tankers, to about 9.50b for general cargo ships, to about 11.25 ship-breadths for container ships.
The presence of another ship in a narrow river will also affect squat, so much so that squats can double in value as the ship pass or cross the other vessel.

How to find out if a ship has entered shallow water?  
1.  Wave generation from the bottom of the ship increases, especially at the forward end of the ship.
2.  Ship becomes more sluggish to manoeuvre.
3.  Draught indicators or echo-sounders will indicate changes in the end draughts
4.  Propeller rpm indicator will show a decrease.  If the ship is in “open water” conditions i.e. without breadth restrictions, this decrease may be up to 15% of the service rpm in deep water.  If the ship is in confined channel, this decrease in rpm can be up to 20% of the service rpm.
5.  There will be a drop in ship’s speed.  If the ship is in open water conditions this decrease may be up to 35%.  If the ship is in a confined channel such as a river or a canal then this decrease can be up to 75%.
6.  The ship may start to vibrate suddenly.  This is because of the water effects causing the natural hull frequency to become resonant with another frequency associated with the vessel.
7.  Any rolling, pitching and heaving motions will be reduced as ship moves from deep water to shallow water conditions.  This is because of the cushioning effects produced by the narrow layer of water under the bottom shell of the vessel.
8.  The appearance of mud cloud will be visible in the water around the ship’s hull when the ship is passing over a raised shelf or a submerged wreck.
9.  Turning Circle Diameter (TCD) increases. TCD in shallow water could increase 100%.
10.  Stopping distances and stopping times increase, as compared to when a vessel is in deep waters.
11.  Effectiveness of the rudder helm decreases.


Every vessel shows different characteristics when it comes to the distance covered when stop signal is given due to difference in dimensions, loading and ballast condition.

It is very important for a navigating officer to learn the principles of passage planning and understand his ship’s characteristics even as a small mistake in understanding may lead to collision, grounding or other kind of mishaps.
Stopping distance of ships
As we all know, ship like any other transport utility does not have brakes to make them stop immediately. When the engine is given stop order, the ship will continue moving in the same direction due to inertia and will come to stop after moving for some distance.
Every ship has two different stopping distances depending on:

1. Inertia Stop
2. Crash stop

Inertia Stop
As described above, when the engine of the ship is stopped, the ship will continue moving in the same direction for some more distance due to inertia. Here no astern command is given (used to produce “braking effect” for ships), and hence ship will travel more distance in the inertia stop method.
Crash Stop
Crash stop is usually the term used when the ship has to sudden stop in emergency situation. Here the engine, which is moving in an ahead direction is given an order for full astern, leaving the rudder in the mid ship position to stop the ship within minimum distance and shortest possible time. To know the complete procedure read for crash stopping read – crash manoeuvring.
In general operation i.e. berthing or departure of the ship from port or manoeuvring through channel or narrow passage, the above two methods are combined for a swift navigation of the ship i.e. in between giving an astern kick to stop and slowing down the ship’s speed for better manoeuvring.
The stopping distance data and chart is given in sea trials of the ship and made handy on bridge for reference. Every deck officer must refer this data to master the navigation of the ship.
The data may differ when used due to variation in weather condition, ships loading, stability and other factors; however, deck officers can compare the trail data and make use of it in practical situations.
Few Practical Examples
Depending upon the loading condition and the speed of the ship, the stopping time will be different when these two conditions are changed.
Also Ships fitted with Diesel machinery will have stopping distances approximately 70% of those fitted with Steam Turbine machinery.
When the ship’s hull has been due cleaning (dry dock) for longer time, the stopping distance and time will be less as compared to when the ship is just out of dry dock. This is because the hull resistance is more in ships with dry-dock done long ago.
The wind direction and sea condition also plays an important role as wind and waves acting from behind the ship will increase the stopping distance and vice versa.
It is important for a navigation officer to know the surrounding of its ship and how the ship will react to change in speed and loading condition. Only then he/she will be able to sail safe through all kinds of seas.

 Berthing the ship using bow-thruster
 Bow Thrusters are fitted normally in the fore and aft parts of the ship. These points of location help to create a turning effect and assist the ship in changing the lateral direction during berthing or departing the jetty
The bow thruster is solely introduced in ships to avoid, or in better words, to minimize the use of expensive tug boats as most of the port state authorities around the world have compulsory requirements to use tug boats for safety purpose.
It is extremely important that the navigating officer on bridge understands the significance of assisting machinery such as bow thrusters during the most critical operation performed by ship and its staff – The berthing of the ship.
Following points must be considered while berthing the ship using bow-thruster:
-   While using thrusters ensure that the ship’s speed in not more then 4 knots as above this the effect caused by thrusters would reduce. This happens because of the merging of the thruster stream with the general water flow on the side of the ship’s hull due to its forward movement.
-   When using a single forward thruster, it is important to concentrate more on the astern as the bow can be controlled by the forward thruster. In such situation, always prioritize to berth or bring the astern of the ship alongside first and then control the ship’s bow.
-   When turning the ship with two thrusters located at fore and astern, the pitch of the thrusters must be opposing each other, creating a turning moment. Massive cargo ships must be assisted by the tugs at the astern part to control the stern movement.
-   When using the bow thruster while the ship is at stop, the astern part will act as a pivotal point. If the thruster is put in the port side, the ship will turn in the same direction.
-   When using the thruster with ship running headway, the thruster’s effect will be slightly less as both the pivotal and thrusting points are now in forward position.
-   When using bow thruster with ship travelling sternway, the pivotal point will be the ship’s stern, which will turn in the same direction as that of the thruster and act as a rudder.
-   It is very important to have an efficient steering gear system as the ship turning by use of thruster is highly dependent on how responsive the rudder (steering gear system) is.
-   Thrusters are used while anchoring the ship. They assist in turning the bow of the ship away from falling anchor to avoid damage by the anchor chains.
Ship Navigation is more of an art which is developed through experience rather than knowledge. When you merge both experience and knowledge, you can definitely Master the Ship’s navigation technique.