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LECTURE no.7

TUG BOATS

Tugs (or tug boats) are vessels designed for maneuvring other vessels or floating units by pulling (towing) or pushing. They are intended for operation in open sea, open roadsted

(radă portuară) and harbors, channels or inland waters. Besides the main function of towing,

tugs are equipped with facilities and equipment to enable the fulfillment of other activities

such as rescue, fire fighting, pollution, ice breaking, occasionally and specific transport.

Tugs are specialized in various types of operations, which lead to different functional and

structural characteristics. The main feature of a tug is its towing power and in direct

correlation with this, traction power on the hook (bollard pull).

Besides tractors feature a tug must ensure other constructive requirements correlated with his

functionality:

- maneouvring and governance qualities;

- towing capacity in any direction;- stability in waves, rough yaw, hauling of towing hawser;

- robust construction;

- protection from run aground (eşuare); 

- good visibility from the wheel house (timonerie);

The features of a tugboat are:

- propulsion system;

- towing instalation;

-system of ship governance.

Fig.1. General Arrangement of a multipurpose tug boat

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Wheel house

Life buoy

Clear display screen

Hull

Railing

Stairs

Chain support

Winch

Spring

Masthead light

Main mast

Flag

HowlerAntenna device

Morse signal device

Pipe

Winch

Hawser

Hydraulic pin

Parapet

Tyre protection

Rudder

Nozzle

Propeller

The tail shaft

Hatch

Main Bridge

Fig.2. Main components of a anchor handling tugs

Types of tugboats

Classification by the operating area:

- unlimited tugs (oceanic class);

- coastal tugs;

- tugs for inland or protected ;

Tugs are differentiated according to the navigation zone and are dictating by their

adaptation to the specific conditions of navigation, respectively to the different states of thesea and ashore distance.

So, for the tugs with unlimited navigation area:

- ships forms are adapted to the navigation in high waves - increased freeboard, bow

raised by one or two levels of forecastle, the increased ratio L/B;

- requirements for intact stability and damage conditions are more severe;

- openings in hull and superstructure are with high sealing;

- autonomy is higher by increasing the storage capacity of fuel, water, supplies and

waste;

- crew spaces are large and designed for long voyages.

As the sailing area (navigation zone) is reduced, the above features diminish.

Fig.3. Oceanic class tugs 

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Fig.4. Coastal tug boats

Tugs classification by propulsion system:

- with axial propulsion line (or Shaft Tugs) (ST) (cu linie de axe);

- with Azimuth Stern Drive propulsion (ASD) (cu sistem azimutal la pupa);

- trailer with Voith Schneider Propulsion system (VSP) (tractor cu sistem cicloidal de

 propulsive Voith Schneider);

- azimutal tractor tug with central azimutal propulsion system (ATT) (cu sistem azimutalcentral);

- combined propulsion system.

Tugs classification by towing system

- towing on hook;

- towing with winces;

- carousel tugs.

Tugs classification by main destination:

- line tugs (remorchere de linie);

- maneuver tugs (remorchere de manevră); 

- rescue tugs (remorchere de salvare);

- escort tugs (remorcherede escortă); 

- anchor handlingtugs (AHT) (remorchere de manevră a ancorelor); 

- multipurpose tugs (remorchere multifuncţionale)

Line tugs  are long distances towing for non-propelled units. are used to transport

maritime barges, offshore rigs, ships left without propulsion, ships under construction, etc.

The main features of these tugs are: sufficient power to ensure the required speed oftowing;

ability to navigate in severe weather conditions; sufficient autonomy. To mitigate the drift

 produced by the trailer (remorcă), these ships are large lateral dimensions (length and draft)

and large side surfaces (drop keels (derivoare), rudders (cârme)) developed to increase the

surge area (suprafaţa de derivă). To increase the flexibility of these ships and exploiting the

high installed power (up to 20,000 kW with traction force of up to 300 TBP (Tonnes ofBolard Pull)), these vessels have specific equipment to rescue and / or escort.

Maneuver tugs  are intended for towing and maneuvering vessels in harbors, channels

and sluices (ecluze), where the towed ship maneuver capabilities are not sufficient. These tugs

are used to guide maneuvers, stop, turning and mooring of vessels. The main features of these

tugs are: sufficient strength to control the towed ship and great maneuvering capabilities. Are

generally equipped with multidirectional propulsion (azimuthally or cycloid) which allow to

reach the pulling force without having necessary to align the tug on towing direction. Towing

installation allows catching the trailer both at stern and bow of the tug. The bow is reinforced

to ensure pushing with the bow on the maneuvered ship. Most maneuver tugs are equipped

with auxiliary equipment that allow them to perform other services in harbor areas such as

combating pollution, fire fighting and escort near the port. In some cases, the shape andarrangement of propulsion have been adapted for easy ice-breaker function for the port and

inland waters.

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Rescue tugs  (or salvage tugs) are primarily designed for rescue vessels in difficulty

(stranded, without propulsion, left rudders or failure of steering systems) and for rescue the

crew of this ship. In general, line tugs (with high power and able to sail in any sea conditions)

are used as rescue tugs if are specific equipments. Among them we can mention: mobile

drainage pumps, fire pumps, diving apparatus, gas masks, vitality devices, maneuvering

cranes, welding and cutting equipments, cables, ropes, portable lighting systems, etc. In

addition are necessary healthcare and human lives rescue equipments, helicopter takeoverarea (not necessarily a helideck), etc.

Escort tugs  have emerged as a result of numerous strandings (eşuări) in coastal areas

resulting ecological disaster. As a result, to reduce the risk of such accidents were issued

international regulations and national rules of navigation. These rules require that all tanker

vessels over 20,000 dwt to be fitted with rapid binding to tug (legare rapidă la remorcher) in

case of loosing propulsion and/or steering systems and to be escorted by a tug specializing in

coastal and port areas. Some port authorities have extended the requirement to other types of

ships also. As a result, in the risk areas was imposed the presence of specialized vessels like

tugs escort.

A tug escort must have sufficient towing power and maneuver qualities so:

ing the trailer with 4 knots in calm water or to keep it stationary against a wind of45 knots;

knots in the same distance as the towed ship stops with

their own means;

on direction when it navigate with 6 knots having the rudder

 jammed (locked) at 35 degrees;

towed ship at a speed of 6 knots on the same circle of gyration that she

made with their own means.

Anchor handling tugs (AHT) are specific ships for offshore oil and gas industry and are

designed for handling and positioning anchors for oil drilling platforms or for pipe laying

ships. Specific for these ships are: being able to work in rough seas; high bollard pull;

additional handling systems (bow and stern thrusters); dynamic positioning systems; largehandle winches; stern roller for anchors cables (chains); open aft deck with anchors storage

and work space. Additionally, the most anchors handle ships are equipped with storage

facilities for specific loads of offshore drilling platforms (mud, cement, chains, pipes, fuel,

water, etc.), these ships bearing the abbreviation AHTS (Anchor Handling Tug Supplier).

Other features of these ships are: wheelhouse with double command at bow and stern; good

view of the bridge; anti -roll systems; starting- lift bridge systems for handling the large

anchors (type A frame).

Multipurpose tugs  combine their nautical qualities with specific features for multiple

functions so they can be used in different situations. Practically any towing is not designed to

 be devoted exclusively to a single function. The most common combinations are: line-

salvage-escort-pollution; fire fighting-maneuver; anchor handling-line-salvage-fire fighting.

Tugs propulsion systems 

The main feature of a tug is the thrust (bollard pull) and direction in which it is

developed. For this, propulsion system is the central element in the design of such a ship.

With some exceptions (salvage tugs and escort tugs) the ship speed on free march is not a

specific requirement. Usually, these speed of the tugs is 10...12 knots. In the case of salvage

and escort tugs, the need to quickly get to the intervention area, the speed is imposed by the

design requirement, usually 15...17 knots.

Propulsion systemSe utilizeaza trei tipuri de sisteme de propulsive: shaft propulsion; azimuthal propulsion;

Voith Schneider Propulsion.

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Azimuth thrusters and Voith Schneider propulsion can orient the force of propulsion in

any direction (multidirectional) and requires no other equipment of governance. Tugs

equipped with multidirectional thrusters can be located at aft (stern drive) or central-bow

(zona central sau prova), bellow the ship. This latter type of arrangement leads to the so-called

tractor tugs. Are usually used the following abbreviations for types of tugs propulsion,

depending on the configuration: ST  - shaft tug - ship with axis line; ASD  - azimuth stern

drive - ship with azimuthal propulsion located at the stern; VSP - Voith Schneider propellers -(in most cases are tractor tug); ATT - tractor tug azimuth - azimuthal thrusters located centrall

 bellow the ship.

a) ST; b) ASD; c) VSP; d) ATT

Fig.5. Tugs propulsion systems 

Shaft propulsion type (ST) ensures the ship governance by the classic system with

rudders. Traction (towing) force is developed only on the longitudinal axis of the vessel and

only to forward; reverse of the ship or side towing is weak. The most common use of this

 propulsion system meets on the line tugs.

Azimuthal Stern Drive propulsion (ASD) provide better governance than the shaft system

and maximum traction force development in any direction. However, the location of the

 propulsion at ships aft makes that the government is realize by rotating entire vessel which

leads to limitation of traction in the transverse direction. This type of propulsion permits

maximum traction both forward and backwards allowing the use of the towing to the stern or

 bow. The most common use of this propulsion system is for the harbor maneuver tugs.

Tractor type propulsion which is provide by placing thrusters amidships (VSP or ATT)help develop of maximum thrust in any direction without needing to return (rotate) the tug,

giving great flexibility in operation. The main limitation of using tractor system is the large

draft (5-8 meters) gave by the location of propellers bellow the ship fact that allow the use of

this tugs only in areas with high water depth. The most common use of this propulsion system

is for the maneuver tugs (where the depth of water permitting) and escort tugs. Except

cycloidal propellers (VSP), all other versions use propeller as propulsion element.

Propulsion Arrangement

Tug design is conduct having in maind the propulsion system as a central issue.

Propulsion system components are: the engine (motorul principal), joint mechanisms

(cuplajulele), gearbox (reductorul), gear drive (transmisia) and propeller.Both for shaft tugs and azimuthally thrusters tugs is applying a few general requirements

regarding the location of the propulsion system.

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- Proppeller position and size  must be correlated with ships forms at stern and with

minimum and maximum draft so:

must be larger as possible, without exceeding the lowest point of

the ship and propeller must be full immersed in the minimum draft. It is recommended that

the tip of the propeller to be below the minimum draft at least (0.2 ... 0.4) from the diameter

of the propeller disc. If the propeller falls below baseline, the ship will accommodate an

extended drop keel (derivor) so that it protects the propeller;ships forms in the propeller area must ensure a smooth water flow and avoid air

absorption of the forward march and minimize the absorption to reverse march;

must facilitate the flow of water, minimize the

loss of efficiency of the nozzle (through blocked areas by contact with the body) and to avoid

the creation of counter-flow on the outside of the nozzle;

must be as far away from the center line, without the risk of hitting the

quay side during roll oscillations and considering the possibility of a proper location of the

engine inside the vessel;

- Positioning of the main engine inside the ship must consider:

forms and the space available in ship's engine room;

ship’s framming, pedestals and others);for engines maintenance (the side, bellow and above them);

main engine (gear, shaft

generator, fire pump, exhaust, etc.)

- Ship’s general arrangement requirements:

 biggest space is given to

the engines. Must be considered also the need for other places in the area (tanks, technical

areas, etc.);

main engine had a significant contribution in tugs displacement and an

incorrect positioning may adversely affect the ship's trim.

s engine room is large and his damage

can compromise the ship’s unsenkyiability. It will seek a compromise between the size ofengine room and its location so as to meet demands for emergency stability (ofcourse, to the

types of tugs to which they are applicable).

Shaft tugs.For these ships the propulsion system items arrangement is "in line". Additionally it will

 be considered:

- be enough space for rudders;

- the axis line bearings will be positioned so that the distance between them to

accomplish the requirements;

- alignment with propeller: in some cases practiced sloping lines into an

vertical plane (for small vessels) and an horizontal one. Tilt of axis line will not exceed 3-4

degrees.

- regarding the distance between the propellers and their inboard distance is

applying the same principles as the azimuthal tugs.

Fig.6. Shaft tugs system propulsion arrangement

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To reduce the angle of the multiple joint shafts, along to the propeller tilt, must be a

longitudinal tilts of the main engine. Must consider the fact that the total longitudinal engine

tilt (static plus the one resulting from the ship's trim) is limited by the manufacturer (must

refer to the engine catalog).

Azimuthal Tractor Tugs.Azimuth thruster location is on ship’s center to bow, under the keel of the ship. Location

 principles are similar to those of ASD tugs type, with the following observations:the location of the propellers on center-forward under the keel of the ship provide a

small level difference between the engines and propellers, making it simple the multiple joint

shafts transmission;

the angle size for thrusters location are given by the ship’s bottom shape;

the existence of a derivative protections extended at aft(drop keel) and bow thrusters

 protection.

Fig.9. ATT system propulsion arrangement Voith SchneiderPropulsion tugs.The location of azimuth thrusters is on center-forward under the keel of the ship.

Location propellers and ship’s  forms must accomplish the strict manufacturer requirements

regarding the thrusters.

Fig.10. VSP system propulsion arrangement 

In Fig. 10 can be oserved that:- the location is for a typical tractor propellers, center-forward under the keel of the ship;

- the angles of thrusters location are given according with bottom shape;

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- the existence of a derivative protections (drop keel) extended at aft end and bow

 protections for propellers;

- transmission with hydraulic gear;

- use of facilities offered by the VSP:

requirement but emprove the

exploitation;

multiple joint shaft for the engine;of generators on multiple joint shaft for the reduction gear.

The towing test (Bollard Pull Test)

The Bollard Pull is the static thrust force developed by a tug in tow line for zero speed.

Bollard Pull is contractual requirement for tugs and its failure caused penalties. To certify

Bollard Pull is performed the towing test. This test is performed after completion of

construction and its mode of progress is dictating by specific rules. The test is conducted by

linking the tug to dock or buoy, bringing engines in nominal parameters of function and

measuring the force developed on the tow line.

There are many definitions of Bollard Pull:

- the average static thrust which measure average force developed over a long period oftime (usually 5-10 minutes) by averaging all values registered during this interval in the

engine rating (100 % MCR ) (regim nominal de funcţionare a motorului). This type of test is

considered as the standard method of measurement;

- the maximum static thrust which measure maximum force developed in a short period

of time (usually 30 seconds) by averaging the maximum values registered during this period.

- maximum thruster is the largest singular value recorded during the test; is informative

and it is considered as the nominal Bollard Pull;

- the “Brazilian” average static thrust which measure the average power developed on

a very long period of time (one hour); due to the inevitable changes in water flow during test,

traction decreases in time and average traction per hour is less than the standard test for 5-10

minutes;- commercial thrust  is traction developed with overload engines (110 % or more) in

order to obtain an "advertisement" of the tug; It is not recognized as official test, but many

vessels are stated in the prospectus with this value for Bollard Pull.

The towing test results are influenced by a number of factors: the ship's position in

relation to the quay; water depth; length of tow ropes; wind and ocean current direction and

speed, etc. To standardize test conditions are imposed regulations on them. Requirements

regarding the development of test conditions are not evenly covered and differ slightly from

one Classification Societie to another.

Towing equipments 

Towage can be done mainly in three ways:

- towing over the stern with stern towing system;

- towing over the bow (not the tugs ST type) with the towing bow system;

- "ear" towing for binding bollards (remorcaj “la ureche” cu legarea la babale);

The towing system (for a ship which contain in here’s class symbol the "TUG" notation)

means all the equipment and facilities that provide the capability of the ship to perform the

following operations:

-towing "straight line"; in this case the towing equipment is placed in the stern-half

of the ship;

-escort towing operations; is performed with towing equipment that is placed in the

 bow area of the ship.

A number of tugs considered as "normal-type" have bow towing equipment (fore towing

 bollard) placed normally to the midlle plane, which allow the vessel to assist a ship or floating

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facility during of towing or maneuvering operations. Such a tug is not classified as "escort

tug" because he must also meet some others specific conditions.

Effective component of towing system is determined by the technical specification of

ship design which contains the shipowner requirements (depending on operations that ship

should execute). Gennerally speaking, the towing system may contain (Fig. 11):

- trailer wires (parâme de remorcă); 

- towing winches (vinciuri de remorcă); - towing hooks (cârlige de remorcă); 

- towing bollard or towing bitt (babale de remorcă); 

- guides or limiters for trailer wires: gobeye, towing pins (ghidaje sau limitatori pentru

 parâmele de remorcă); 

- stern roller which is specific for ST type vessels (rulou de ghidare pupa);

- tow bars, as safeguards on the ship against trailer wire (curbe de remorc ă, ca

elemente de protecţie pe navă faţă de parâma de remorcă). 

Fig. 11. Towing system components

Trailer wir es

Trailer wire is an elastic and strong link between tug and towed vessel. Trailer wires or

cables are made of steel wires or synthetic cables and requirements on the characteristics of

materials that run them are governed by Rules of Classification Societies and may differ from

one classification society to another.For example, the recommendations in the document "Guidelines for the Approvability of

Towing Vessels"  edited by "Noble Denton International Ltd."  specify as follows:

-ocean-going salvage tug –  3pcs. (1pc. reserve) each of 800m;

-tug for unrestricted towages –  2pcs. (1pc. reserve) each of 650m;

-tug for restricted towages 1pc. of 650m.

Another cryteria is according with displacement of towed vessel.

Displacement of towed

vessel [tones] 

Length of the towing wire [metters]

   

450 170 - 180 300 - 350

800 200 - 220 400 - 4301800 260 - 270 500 - 550

4500 300 and more 600 and more

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In setting of minimum breaking strength of trailer wire, according with is choose the

diameter of the trailer wire, either steel or synthetic fibers, it leaves by the value of "Bollard

Pull" (BP) imposed by the ship specification, which apply a safety factor greater than one, and

whose value is different from one classification society to another, with one exception:

minimum breaking strength value will never be under 2xBP.

Towing winches

Usually, to improve maneuvring characteristics, towing winch is placed onto ship in themiddle plane and at a distance of 5% to 10 % of the ship ’s  length, aft from amidships.

Classification Societies Rules stipulate a number of requirements on towing winches:

- drum winch will be disconnected from the drive shaft and must be fitted with

 pneumatically or hydraulically band  brake (frână cu bandă), and compulsory with manual

 brake on the winch;

- capacity of the brake drum (brake holding load) considered on the first layer of

windings (first on the drum) is ;

- the control winch will be both in the wheelhouse and local;

- will be ensuring release option for the drum brake for any working condition of towing

winch, including in case of failure of the drive unit;

- it is advisable to provide a system for measuring and indicating the load (the force) in

the towing wire, wich must be readable both local and wheelhouse;

- will be ensuring correct wire winding on the drum by providing a specific mechanism

(cable shooter) (depanator de cablu);

- will take into account that usually the output cable on the drum must be at the stern to

the bottom of it, to not damage the ship stability and to induce lower forces in the ship’s body.

Towing hooks

To locate the towing hook on the ship, the requirements of Classification Societies Rules

are similar to those for the towing winch. To choose the towing hook, must consider the

nominal traction on hook:   (nominal traction must be equal to bollart pull). For

execution of the towing hook will consider the following requirements of ClassificationSocieties Rules:

- the strength of the hook will be calculate for a theoretical hook force given by relation:

, where c  is a safety factor greater than one, whose value is different from a

classification society to another;

- towing hook construction and fastening to the ship will ensure rotation of it into a

vertical and horizontal plane.

- the towing hook will be equipped with a fast releasing rope shutter (sistem de

declanşare rapidă a parâmei) able to function in emergency and with the hook under load. The

trigger can be actuated mechanically, pneumatically or hydraulically and its command will be

 both local and from the wheelhouse. Automatic triggering system must operate under load

hook and in case of some transverse floating wich can be dangerous for the ship stability

Towing boll ard or towing bitt

A towing bollard (or towing bitt) is a solid, welded construction, made of pipes, having

 portal shaped - "Π" - encased into the hull and which is placed between the towing winch and

stern of the ship, having the role of maintenance (guidance) of towing wires (ropes) from the

towing winch to the inside of portal. Tugs that can assist another vessel during towing or

other maneuvers are also equipped with towing bollard on the bow area, and the workforce is

considered to be .

Towing pins

These are vertical cylindrical elements located on stern of the ship, symmetric on themiddle plane, having the role of guiding / limiting of towing wires. They have a strong built,

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embedded in the hull. Can be fixed or with telescopic construction. The towing pins are

designed to prevent the towing wire to deviate laterally over the ship railing.

Gobeye

It is a guiding robust element, embedded in the hull, executed from round steel or cast as

a guide hawse (nară de ghidaj) - similar to those used for mooring ships. This guide is placed

into the middle plane, its role being to guide through it the towing rope fixed to the towing

hoock.

Stern roller

It is a guide element specific for combined ships (supply vessel / tug vessel) that can

 perform towing operations, anchor handling operations or harbor buoys handling operations.

Constructive, the stern roller guide consists of a welded cylinder with diameter from 1m to 4

m, having an horizontal axis located at stern and with axial bearing embedded in the hull. Its

role is to protect the stern and facilitate slip of towing rope.

Towing maneuver

Certain basic principles apply to towing.

One is that the attachments to the floating structure, drilling platforms or another shipmust always be sufficiently strong that they do not fail or damage the structure under the force

that parts (breaks) the towline. The actual breaking strength of wire rope is typically 10% – 

15% greater than the guaranteed minimum breaking strength. Actual breakage will usually

occur under a dynamic load rather than a static load. It is important that under overload, the

structure or vessel being towed remains undamaged.

A usual requirement is that the ultimate capacity of any towline attachment to the unit be

at least four times the static bollard pull and at least 1.25 times the breaking strength of the

towline from the largest tug to be used on that attachment. At least one spare attachment

 point, with pennant, should be fitted for towing ahead, to be used in case of emergencies.

A second principle is that the towing force must be able to be resisted through a

significant range of horizontal and vertical angles, thus imparting shear and bending, as wellas tension, on the towing attachment.

If a towline does break at sea, it is desirable that it fail at a known “weak link” so that it  

may readily be reconnected, even in high sea states. A typical arrangement when a single boat

is towing with a bridle is shown in Fig.12.

Fig.12. One tug - one tow typical arrangement

If the towline is subjected to a high impact overload, the short pendant between B and C

 breaks, the shackle at B is pulled back on deck by means of a fiber rope pendant, a new

 pendant fitted (BC), and the towline reconnected. To reduce shock loads in the towline, eitheran elastic fiber pendant catenary may be used or a length of chain installed in the belly of the

catenary (Fig.13).

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Fig.13. Towing configurations

During passage through restricted waters and during final positioning, the towline may be

shortened in scope to permit better control. If it is too short, however, the thrust of the

 propeller’s wash will react against the towed vessel. 

The inertia (momentum) of a towed structure, especially a large one such as an offshore

caisson, is tremendous. It tends to keep moving ahead long after pull has ceased. A constant

concern of boats when towing in congested traffic conditions or in ice is that if the boat is

stopped, the towed vessel or structure may overrun it. Further, due to the inertia of the towed

structure, it is difficult to slow it or change direction

Fig.14. Towing a drilling platform

In a narrow channel additional boats may be used alongside and also astern. The boats

located astern are being dragged backward; when needed, they can go ahead on their screws

and thus slow the towed structure. However, being dragged astern, there is a tendency for

them to be pulled down and swamped, so special stern sheets are usually fitted and special

attention paid to watertight closures on the boat, since otherwise the engine room door may be

left open, regardless of the published instructions.

When towing out in the open sea, the boats lengthen out their towlines to offset the wide

range of loads in the lines due to the waves and swells. When towing a very large structure in

coastal waters, a single lead boat may run ahead to verify route, confirm depths by forward-

looking sonar, and pick its way through underwater obstructions, or ice. Such a lead boat can

also warn other shipping. If the towed structure is a deep-draft vessel (some of the offshore

 platforms have drawn 110 – 120 m), then the towline, if attached to the structure below water

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near to the center of rotation, may have a steep inclination. This will tend to pull the stern of

the boat down into the water. Therefore, the towline may be led up to a pontoon or buoy,

which will resist the vertical component of the towing force. Such a buoy should be

foamfilled to prevent flooding in event of a leak or hole (Fig.15). Such a system may also be

useful when towing through broken ice to minimize the shock loads in the towline itself.

Fig.15. Towline arrangement for deep draft towRescue towing maneuver

Prepari ng to maneuver the tug vessel

Tug ship runs following preparations:

- bunkering and food supplies;

- boarding on board at least 2-3 trailers reserve (remorci de rezervă);) 

- if the weather is rough will take on board some floating objects which will serve for

trailer transmission an support (drums, buoys, plates, etc.)

- during the approaching of tug vessel to the towed ship, the trailer (arranged in loops)

sits on the deck;

- preparing the haulings (bandule) and hauling launchers (lansatoare de bandulă); 

- it will contact by radio, optical and acoustic means the ship to be towed;

In case of non-specialized towing operations ships, will be strengthened the stern bollards

 by fixing a resistant belt consists of wire ropes or chains, will be use various types of wire and

chain stoppers, stretching, and other necessary deck accessories.

Preparing to maneuver the towed vessel

Vessels requesting assistance in offshore tugs is clearly damaged and their damage can

not be remedied by onboard facilities.

Damaged vessel shall submit the following data:

- the position where she is and drifting direction;

- the damage that occurred;

- nature of goods transported;At the ship to be towed, perform following preparation:

- will stopping one of the anchors (se va boţa una dintre ancore) to use heres chain as a

trailer (if necessary);

- prepares a trailer that will be fixed with one end to the bow and the other end will be

led at stern by board wind; to this end will tie a long hawser (saulă); 

- prepare several haullings and check the haulling launcher;

- winches and capstans (cabestane) are prepared for use in trailer recovery;

- preparing a boat for water released for trailer transmission through it if that is needed.

 Note: if the damaged ship is near the coast, then must have to lay off an anchor to avoid

stranding the vessel.

The tug will be informed about the position of the damaged vessel in relation to thedirection of action of the wind, as follows:

- ship with stern castle will be in position with the bow in the wind;

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- ship with higher center superstructure will have the wind about one point of compass

 behind abeam;

- ships with high superstructures from bow to stern will be positioned with broadside on

wind;

- ship with bow castle will be in position with the stern in the wind;

When towage is carried on short distances, the towed vessel transmits the trailer to the

tug.Towing maneuver execution

Towing maneuver includes the following operations:

- nearing the tug to the vessel to be towed;

- transmission and connecting the trailer (the towing wire);

- departure and march with towed ship;

Towing methods:

- towage in slipstream on the sea (remorcajul în siaj pe mare);

- ear towage (board on board towage) (remorcajul la ureche)

- towing by pushing

Towage in slipstream on the sea

Is a towing method often used both on open roadsted 

and on large distances on the sea.The advantage of this method is that can be used as a towing vessel, regular merchant ship

(non-designed for towing).

Towing procedures:

a) Towage bow before  - the towed vessel may use their own steering system and the

drag is lower than the stern tow before towage method (Fig.16);

 b) Towage stern before - is rarely used and towage is carried on short distances and in

tight spaces. When the vessel towed was a water hole in the bow, then it will proceed to the

towing system with stern before (fig.17).

towed vesseltrailer tug

vessel

 Fig.16. Towage bow before method

towed vessel

trailertug

vessel

 Fig.17. Towage stern before method

Disadvantages if the slipstream tow the stern before:

- can not use the steering of the vessel towed;

- drag through the water is very high;

- higher tensions appears on trailer;

- speed reserve is low during the tow.

Towage in sli pstream on the calm sea

Towed vessel has functional steering system.

Towage procedure (Fig.18):

- nearing the tug at a side distance of 30-35 meters on a road parallel to the longitudinalaxis of the towed vessel;

- (1) position correspond with the moment of trailer transmission with hauling launcher;

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- establishing trailer with safeguarding on towed vessel (distance of 60 meters between

ships)

- departure with "very slowly" speed (progressive stretching of the trailer), increased

speed after the trailer is spread.

 Note: Towage in slipstream on short range (harbor maneuver) is performed as shown in

the previous case, but the distances between ships are smaller (usually 20 to 30 meters, on

weak wind, the distance can be 5 to 10 meters).60 meters

30-35 meters

wind

 

Fig.18. Towage in slipstream on the calm sea

Towage in sli pstream on the rough sea

Ship to be towed is into the wind with bow and is ready to give or receive trailer. Tug can

not usual convey the trailer.

100 meters

drifting towed vessel 

80-100 metersapprox.

100 meters

towing vessel 

“STOP THE ENGINE!”

trailer transmission with

hauling launcher

wind

 Fig.19. Towage in slipstream on the rough sea

SITUATION 1:

- nearing of the tug is made with "VERY SLOWLY AHEAD!" speed (position (2), (3));- at 80-100 meters from bow of the towed ship, is given the "STOP THE ENGINE!"

command and is launches the hauling;

- trailer length is about 400-600 meters.

SITUATION 2:

- damaged ship will launch on the water a buoy connected with a hawser line (saulă) of  

200 feet long, which will link from 30 to 30 meters lifebuoys and the end of hawser line is

connected to the trailer;

- tug maneuvering on stern of the damaged vessel at a distance of at least 100 meters

will "fish" buoy, implicitly the trailer and will travel on bow of the damaged vessel.

Ear towage (board on board towage)

The method is used to tow small vessels on short distances. Ear towage is done on calmsea and, with high priority, inside the ports.

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Fig.20. Ear towage (board on board towage)

Linking of towing ship to the damaged ship is done by taking into account:

- damage suffered by the vessel to be towed;

- the position of the vessel to be towed;

- wind direction and his strength;

To tow a vessel with damage to the steering and propulsion system, on the port area, on

the calm sea, must execute the following operations:

- nearing the tug alongside to the damaged ship until the stern is reach, then will put therudder left (right) to nearing the itself bow to the damaged ship;

- when the bow of the tug is up to 5 to 10 meters from the damaged ship the engine is

stopped;

- the "cross" connections are made (previously was handled the haulings for placing the

contact ropes on position);

- mooring balls (fenders) will be placed between ships to protect both ships;

- the departure of the convoy will be made with " VERY SLOWLY BEFORE " speed

and then gradually increasing speed.

Attention!

On the wind and mounted sea ear towage is not recommended because damage can

occurs to vessels engaged.Towage at sea by pushing

It is a method (process) rarely used in open sea and can track the following purposes:

- transport of barges in the harbor road (rdă portuară); 

- transport of various floating objects over short distances.

towing vessel 

barge

 Fig.21. Towage at sea by pushing

For more effective loading - unloading operations in ports, specialists have developed

couplings "tug - ocean barge." System of towing.

The Breit Ingram system: tug's bow are a pear shape and engages with stern barge,

 being a unitary system with a solid coupling; disconnection of the barge is done by pushing its

 by a hydraulic piston; the system develop an economical speed of 14 knots.

The Carpot system: the two bodies are coupled by sliding cones; develop an economical

speed of 10 knots.The Catug system: the two bodies are coupled by means of hydraulic rods; develop an

economical speed of 14 knots.