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The watchkeeping both in port and at sea is considered the fundamental duty of any deck officer who normally receive a mandatory training related to the. A position aboard the vessel about which the ship rotates when turning is called the pivot .. A distinct ship-handling advantage is obtained by being able to stop. Управление Судном. Теория и практика / Ship Handling Theory and practice. Year: Language: english. Author: D. J. House. Genre.
According to the ratio of the ship's rolling or pitching period to the wave period, the ship will pitch and roll over the waves, or just break the waves and absorb kinetic energy. With a self propelled ship, water is taken away from the bank to the centre of the canal by the propeller. It also decreases vessel vibration and noise levels. The drag of the anchor varies inversely with the speed of the ship and. Particular items dealt with in these lectures are illustrated either by including them as part of an exercises or by a separate simulator demonstration. Momentum is discerned by the shiphandler in terms of his judgement of speed. On larger models.
Its movement can be easily instrumented and its forces can be physically felt by the pilot. A great many procedures and processes in the industrial world lend themselves to the kind of training in which definitive actions at specific times can be taught in advance. The controlling device can observe the forces represented and respond by driving the controls according to the instructions built into it.
It leaves turbulence far behind. It involves combinations of variables so numerous and complex that no amount of detailed predetermined instruction can bring a ship through a canal or dock it. Each time a ship moves. In all the foregoing examples there is a minimum of turbulence. On land. In the air. In the cases of vehicles operating with positive traction. In recent years we have all seen how successfully space manoeuvring can be accomplished by instructions electronically memorized in advance and self adjusting in flight.
But what goes into the making of these few commands? How far in advance must each decision be made before the vessel can be expected to respond? What does the shiphandler have to see about him and what does he have to see in his mind's eye? Try to list in detail all the things that you must be aware of that allow you to feel the ship. If the correct instructions. Consider a ship a thousand yards away from a berth under normal conditions for docking.
For many years it has been feasible to programme flight instructions into electronic devices and either make unmanned flight manoeuvres or use these instructions to create flight simulators that are realistic enough for training and research. The design of such computers is based on a mathematical model which represents the real vehicle and the real influences affecting its motion.
In many respects a large ship is the most difficult of all vehicles in the world. Study and observation come first until accurate foresight is developed.
Know your ship. He can't see bank cushion. He can't see the turbulence or feel its effect on the ship. A control computer knows how to control a space vehicle because its thinking is based upon mathematical models. How then does the pilot get his job done?
He can't see inertia. It is becoming harder and harder to see the ship responding and to observe critical differences in a ship's speed.
Physical feel on ships of any size is non-existent. Visual aids and instructor presentations. It has not been feasible. He can't see the side pressure on the rudder. An examination of existing fundamental concepts in the light of the characteristics of modern large displacement vessels. Speed is more or less determined indirectly by telltale signs that indicate speed.
The only direct visual observation we can make is that of distance. The influences that one cannot see are becoming more and more important. Practical experience is most important. Know your surroundings. There is less and less that a pilot can see and more and more that a pilot must know as ships get larger. How is it developed? Knowledge is the predominant factor. Discussion on tracks recorded during Lake Practice.
It is therefore important to make a serious review of shiphandling fundamentals. Development of new handling concepts specifically applicable to larger modern ships. Exchange of ideas and experiences. In order to reexamine the fundamentals of shiphandling thoroughly. Know what is happening and what is going to happen. An effective mind's-eye-view comes from a thorough knowledge of ship. The proportion between the ship's safe handling speeds and all the other factors affecting her becomes much greater as ships get larger.
Know what you are going to do. As ships grow larger. Know the alternatives. The skilful application of these comes only through a great deal of practice.
Good foresight is judgement when you select decisions and timing from it. This requires knowledge and experience and the use of one's imagination. Know when to do it. Feel is a conceptual appreciation of the ship's characteristics and is extremely important. In very confined waters if there is any doubt whatsoever just go as slowly as is safe. In confined waters.
Remember one has more control over a ship when increasing speed than when decreasing speed. An experienced pilot should be able to stand quietly on the bridge and take bearings and plot them more accurately in his head than most people not familiar with the waters can plot them using instruments.
When large loaded ships are berthing. When winds and currents are within safe working limits. How one should think of speed is a personal preference. While reducing speed in cross wind and current. Sighting over the jack staff from the exact centre line of the bridge is best but. Only when the ship's head is in line with that point is there no longer any drift or lee occurring. He keeps a continual plot and he knows all the significant distances from the ships.
When the surroundings become too confined to use gyro headings any more. Whenever it is considered prudent to have someone standing by the anchors. If there is any angle of drift. If the question arises whether it is safe to attempt a manoeuvre because of strong winds and currents. When turning in confine surrounding. As larger displacement ships are built. This saving bank of imposed forces must be kept in mind by the shiphandler for every subsequent action. The greater a vessel's displacement the greater her inertia and momentum.
At all times keep aware of hazards and keep aware of ways out of trouble in case you need them. Know what these should be at every point in your approach. If that may be too fast or too slow. Displacement The larger the ship. The advance plans get things moving in the right direction.
One must know ahead of time where to check speed. This means simultaneous. From the foregoing it is evident that if both vessels are to be stopped in a given distance. This is not based on guesswork but past practices in the waters. In effect. The more accurate they become through practice and concentration. Make the necessary adjustments ahead of time. Know before you get to significant points in your approach how you want the ship to be.
At all times have in mind a clear idea what your speed is and what it should be. Too often. These pre-planned actions become routine with harbour pilots with appropriate estimated variations for conditions. These tendencies often have emotional causes from a lack of knowledge of the ships and the surroundings. Continually evaluate your direction of movement. When in doubt. When in doubt make adjustments with enough margin of safety to make up for any doubts. In most cases engine power is based on the amount required to overcome underwater resistance at a desired speed.
Skill and judgement are further aided by good pre-planning of the manoeuvre. Make all decisions early.
Momentum is discerned by the shiphandler in terms of his judgement of speed. Some people tend to be impatient after deciding what to do and take action too early. Choose speed accordingly. Speed headway is your worst enemy unless you actually need it.
Skill and judgement come from good old-fashioned knowledge. You have anchors on a ship to be used. Timely application of knowledge comes through practice and analysis of what you have done and what you might have done.
Mother Nature. We believe generally that: Why training …?!
Under water resistance forces due to the drift W. With headway. Centre of area of dead works R. Wind induced forces make the ship drift Fu. These forces. Port Revel Shiphandling Course Manual 5. Consider the current in the vicinity of confined waters.
The current at different points across and along a river, or in and about port facilities inside a harbour and across the ends of jetties, varies in strength tremendously and frequently eddies in the opposite direction. The current may be nearly uniform against a short, small vessel over its entire length. But a 1,foot long tanker may have an entirely different force or direction acting on one end than on the other end during a stretch of river or harbour steaming.
Furthermore, the large ship's speed in terms of ship lengths per hour is a very small fraction of the speed of the small vessel in terms of her ship lengths per hour whilst crossing a variable current even though their actual speeds are the same.
The current affects all ships equally until they begin to cross lines of changing current. Then the large long vessel has much greater difficulty than the smaller vessel.
The effect of the current increases drastically when the under-keel clearance reduces. When a long ship is steaming or turning in restricted and confined waters, the under-keel clearance can be quite different at different points of the keel, and thus, in spite of a uniform current, the induced current forces will be different on each part of the vessel, resulting in rotation of the ship.
If the current speed is different from one knot, multiply these figures by the square of actual current. Hundreds of tons: A one-knot uniform current will have exactly the same effect on the speed of a 10,ton vessel as on a ,ton vessel, but the momentum of the first will be changed by the amount of 10, tons-knot while the change in the momentum of the other will be , tons-knot because of the difference in inertia between the two vessels.
According to the ratio of the ship's rolling or pitching period to the wave period, the ship will pitch and roll over the waves, or just break the waves and absorb kinetic energy. This has been known to happen in calm.
At certain stages of the tide. It usually does not endanger smaller ships because their surging does not carry as much momentum as the surging.
He admitted the hoax shortly before he died in Adverse surging is particularly evident in Pacific Ocean ports. Although the initial oscillation may be hardly discernable.
Seiche may be caused by meteorological events such as moving low pressure front. This photo was acknowledged as a fake. It may not be evident to the eye nor evident on smaller vessels. Tugs from Multraship and URS pushed Pelican 1 onto a sand bank immediately after the collision to remove her from the narrow and busy Nauw van Bath shipping lane … and to avoid the risk of Pelican 1 sinking. For further information. The ship was named Olympias. The cruising speed may have been 6 kn. By John Morrison.
Her length is 37 m. John Coates and Frank Welsch in There were usually men on board. Difficult to start in reverse when making good headway. Quick starts and stops of propeller while manoeuvring at slow speed. This is the most common type of propulsion for almost all the ships today..
Older types are limited with regard to the number of starts that can be made in a given period of time. Are very handy. Backing power is limited. Turbines are capable of very low R. Low R. Turbo-electric or diesel electric. Full power is quickly available ahead or astern.
Takes time to build up or reduce R. This affords greater facility when working engines against a mooring line or anchor. Steam Turbine. When using a "touch ahead" to regain steering. Brown in Baltimore.
Steam reciprocating engines are not in use any more. Removal of the shaft line. It also decreases vessel vibration and noise levels. In addition. With cpp or turbine.
Turbine is similar in that to a Controllable Pitch Propeller. For this reason the Port Revel ships are set quite often with their turbine option. With a motor you will have to stop from time to time and even to back the engine and give a kick ahead to keep control. The main drawback of turbine engines is their slow acceleration which requires more anticipation from the pilot.
When going astern. Single screw propellers right-turning: This results in a pronounced swing to starboard. When going ahead. Turn to port: Both propellers turning clockwise. Only fore-and-aft thrust remains. Rudder amidships: Both propellers turning ahead or astern same R.
Turn to starboard: Both propellers turning counter clockwise. The other part is thrown downward against the lower starboard side of the rudder. As the single screw race spirals astern of the propeller. Transverse propeller thrust plays an important role and its effect varies with the size and area distribution of the rudder and stern form.
A great many twin screw vessels do not have this advantage. A rudder is efficient in steering a ship only due to the fact that a strong water flow from the propeller hits it.
If you wish to limit the speed reduction. Steering force is 75 t at Half Ahead … Sogreah. It is a good thrust on the rudder for a short time without gathering too much headway.
Due to inertia effects. The greatest benefit of that is when you start from the ship dead in the water. This explains the higher side forces shown above. Crenshew — US Naval Inst. At higher speeds the hydrodynamic flow provides an additional turning component which increases the total turning moment back to the zero speed value. Be sure to safeguard against the dangers presented by a ship's anchors when working with tugs.
Be sure safeguards are taken to avoid crowding a tug between other vessels. Before having a tug let go a stern line. Whether breasting a ship bodily. When using tugs. To hold a ship stopped in a broadside current or broadside wind.
For instance. To increase or decrease a vessel's movement. It is the tug's duty not to lead too broadly from the ship and it is the ship's duty not to carry too much stern-way at times such as this. To turn a vessel when stopped. Whenever a tug is used to tow a ship on a line from the tug's towing bits. This off-centre strain will list the tug and. Due to relative motion.
When entering or leaving a berth, particularly a berth alongside a pier or wharf, mooring lines can be used in conjunction with engines, particularly steam turbine engines, but cannot be expected to stand the strain of the vessel in motion. With very little motion, a large displacement vessel will break any number of lines of the very best material.
However, by using the engine to control the momentum of the vessel until she is stopped over the ground without putting a heavy strain on a line, the engine can be kept in balance against a line so that its force can be utilised. For example, barring adverse wind or current, even the largest ship in the world can be "breasted off" the face of a pier on a good spring line with careful use of the engine.
The trick is, of course, to have the ship's momentum arrive at nearly zero at the time the line becomes tight. With extremely large displacement vessels, it is common practice to get all movement off the vessel by means of tugs, engines, anchor, etc. A good example of a fixed Pivoting Point. Ships have a mobile Pivoting Point. With normal rudder action, the Pivot Point is located somewhere in the fore half of the ship.
With bow thruster activated, the Pivot Point moves aft. The bow thruster can be used in combination with the rudder to simultaneously: Stand on the port side of your ship when you turn to starboard.
The larger the drift angle. From position A: These effects are much reduced on shallow waters. When a ship enters shallow waters. Friction and turbulence are increased and the wave form changes. The same volume is needed to replace the space left by the passage of the hull at a constant speed.
Diameter of turning circle increases. More ship's power is absorbed by the water due to increased friction. Turbulence interferes with rudder and propeller effectiveness.
Larger waves and troughs are formed and the ship "sinks" closer to the bottom than she would do at the same speed over the ground in deep water. At the same time the ship's trim changes: PP moves more aft: Ship's speed.
The shape of the wave form depends on the shape of the hull and the speed of the ship through the water. The wave form consists of: Since water is fluid.
Pressure in tube test drops when diameter of the pipe decreases: Higher bow wave two dimensions. Since the shape of the two ends of the ship is different and according the position of the wave form relative to the ship.
When the side clearance is limited by a slope or a bank at a distance less than the width of influence. These distances are called the depth and the width of influence. When the bottom clearance is less than the depth of influence. This is particularly noticeable in the supply flow to the propeller which drives the water away a little faster than the water can flow in. The result is a "cushion" effect between the bow and the bank.
Propeller suction "Suction" in shallow water exists at the stern. The increased suction on the shallow side begins to act and the stern is drawn toward the bank. The direction of this force is not only horizontally outwards from the bow. This depresses the surface at the sides just forward of the propeller. As a result. The bow wave becomes higher on the side toward the bank and the increase in pressure.
When the sea bed is regular. As soon as the ship gets slightly away from the centre due either to her steering or an irregularity in the canal.
The saturation speed depends mainly on the blockage factor. There is a "saturation speed" when the ship becomes very difficult to control due to restriction of water flow. The waves and troughs about the hull are steeper and larger than before. The ship is in a balance between these forces only when she is in the centre of the canal section.
Not only is there a restriction on the flow of water under the ship. The banks act as a cushion on both sides of the bow and cause suction on both sides of the stern. Max speed: A lower water level is seen in the middle of the ship Q. With a self propelled ship, water is taken away from the bank to the centre of the canal by the propeller. This induces suction of the stern to the bank. Straight section of channel or canal - Stay in the middle of the canal or just off the centre line.
Channel bends The bank cushion can be used to advantage in safely making bends in a narrow channel or canal by favouring the right side when the canal bend is to the left and by favouring the left side when the bend turns to the right. The ideal track round a bend is the one that lets the ship follow the canal with the least amount of rudder.
Channel or river bends with a current - When heading downstream, stay close to the middle of a channel bend. Two sound basic principles, but in rivers or channels with current and irregular banks, extreme caution is necessary when good local knowledge is not available.
Special anchors can have a holding power in excess of The nominal chain breaking load is normally around 4 times higher than the holding power. This must be compared to the holding power of the anchor on the bottom. Roll continue and anchor begins to come out.
After R. Ready to dig out completely. Anchor upside down.
The movement of the chain in resuming its larger catenary will impart a velocity to the anchor over the velocity of the ship and cause it to skip along the bottom. On the other hand. Increases in speed may cause the anchor to jump under a strain which has straightened the catenary.
Ship's speed when dredging should be as low as is necessary for manoeuvrability. Dredging an anchor is dragging an anchor on purpose. The drag of the anchor varies inversely with the speed of the ship and. When used for dredging. This in turn depends on the vessel's speed. A leeward anchor may even lead under the ship to windward enough to cause a swing in the opposite direction.
The lead of the chain from the hawse-pipe is not always a true indication of the lead to the anchor. Using a lee anchor can be very effective in holding a ship to windward because it allows a very flat catenary from the ships bottom toward the anchor. The reasoning behind the actions of the ship handler will tend to be based on the associated theory at the root of any handling operation.
Such knowledge — coupled with main engine power and steering, anchors and moorings, tugs and thrusters, if fitted — can be gainfully employed to achieve a successful docking or unberthing.
Practice with different ships, and fitted with different manoeuvring aids, tends to increase the experience of the would-be ship handler. Training for junior officers to increase their expertise in the subject is unfortunately extremely limited.
The theoretical preparation, the advance planning and the execution of any manoeuvre will not materialise overnight. And an understanding of the meteorological conditions may not initially be seen as a relevant topic, but ship handling against strong winds with a high freeboard vessel is somewhat different to manoeuvr. Reply Toggle Dropdown Quote.
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