Section 2 Classification Guidance

2.1.1 The Hull design and construction requirements for tugs are all contained within the Rules and Regulations for the Classification of Ships, July 2022 and both vessels with the Type notation Tug or Escort Tug are to comply with the Rules and regulations of this Ruleset to be eligible for classification with Lloyds Register.

The content of each of these sections is generally self-explanatory with content referring out to other sections of the Rules and Regulations for the Classification of Ships, July 2022 to be complied with and/or listing additional requirements or exceptions.

Of particular interest in the above is Pt 4, Ch 3, 7 Towing arrangements and Pt 4, Ch 3, 8 Fenders (additionally Pt 4, Ch 3, 9 Escort operation, performance numeral and trials for Escort Tugs), these are discussed in the following sub-Sections.

2.2.1 The Rule requirements relating to the towing equipment and their foundations are contained within Pt 4, Ch 3, 7 Towing arrangements of The Rules and Regulations for the Classification of Ships, July 2022.

In addition, materials used in towing equipment should comply with the applicable class requirements for materials. Class certificates are generally required for the materials used for winch drums, drum shafts, winch brake components, winch supporting frames, towing hooks and towline guiding fittings installed upon classed vessels.

2.2.2 Documents to be submitted

Additionally, where deemed necessary by Lloyd’s Register, buckling and/or fatigue analysis, performed in accordance with a standard or code of practice recognised by Lloyd’s Register, may be required to be submitted for information.

2.2.3 Consideration of the design load

The DL (in the Rules and in the table) take into consideration the assumed dynamic effects through the application of the dynamic amplification factor (DAF) which is clearly designated in square brackets in Table 2.2.1 Design loads: tug (see also Ch 1, 1.3 Definitions 1.3.4).

2.2.4 Design requirements for towing winches

The Rules require that the scantlings for towing winches (including winch drums, drum shafts, brakes, support frames and connections to the hull structure) are to be determined by direct calculations using the Design Loads (outlined in Table 2.2.1 Design loads: tug)

2.2.5 Additional design guidance for towing winches

In addition to the Rule requirements outlined in Ch 2, 2.2 Towing arrangements for Tugs 2.2.4, the following design guidelines should be followed.

Towing winches should generally be arranged in such a position (noting the position of guiding fittings and towline path) as to minimise heeling moment due to the towline force.

The winch brake should normally act directly on the drum and should be operable (either manually or otherwise) in case of failure of the primary power supply system.

The towline attachment to the winch drum should be provided by means of a weak link or equivalent.

Towing winches should be provided with an emergency release system as described in Ch 2, 2.2 Towing arrangements for Tugs 2.2.10.

The dimensioning of the winch drum should take into account the rope bending specifications provided by the towline manufacturer.

Due consideration should be given to the proper spooling of the towline on the winch drum, as well as preventing the towline slipping over the flanges of the drum.

Towing winches may be equipped with an active pay-out and haul-in system automatic adjustment of towline. In such a case, the relevant requirements of Ch 2, 2.3 Towing arrangements for Escort Tugs 2.3.6 and Ch 2, 2.3 Towing arrangements for Escort Tugs 2.3.8 should be complied with.

It is recommended that the towing winch should be fitted with equipment to continuously measure the tension (mean tension, tension peaks and slack line events) in the towline.

In case a towline measurement system is installed on board, the measured data should be displayed on the bridge.

2.2.6 Guidelines on testing of towing winches

The following guidelines outline the appropriate testing regimes for towing winches installed on board tugs.

Towing winches, including the associated emergency quick-release devices should be load tested at the DL, as defined in Ch 2, 2.2 Towing arrangements for Tugs 2.2.3, or the BHL, as defined in Ch 1, 1.3 Definitions 1.3.5, whichever is the greatest. Generally, load testing should be conducted at a specialised facility equipped to generate the required line tension (e.g. maker’s premises) and witnessed by Lloyd’s Register.

In case a towing winch is of conventional, proven design, for which load testing has been previously performed in a manner deemed acceptable by Lloyd’s Register (evidence and results of load testing should be supplied), it may be sufficient to perform on board function testing in accordance with the guidelines specified below.

The proper functioning of the towing equipment should be verified by on board testing witnessed by Lloyd’s Register. Function testing should be performed both for normal operating conditions in accordance with the towing arrangement plan (see Ch 2, 2.2 Towing arrangements for Tugs 2.2.2) and for emergency conditions (emergency quick-release, failure of main power supply). The safe operation of the towing winch from all control stations should be demonstrated.

Towing winches should be function tested on board. The correct functioning of the winch brake, the load carrying winch components and the associated supporting structure should be demonstrated at a towline force equal to the bollard pull, as defined in Ch 1, 1.3 Definitions 1.3.1. The emergency quick-release should be function tested under normal power supply conditions with a towline force corresponding to the minimum thrust (engine(s) clutched in and running at idle speed), as well as in a dead-ship condition (without strain in the towline).

Winch operating modes which should be function tested include hauling in and paying out of the towline, as well as braking.

Hydraulic and electrical systems should be function tested on board in accordance with Lloyd’s Register’s requirements for machinery and electrical systems.

Operational tests should be performed by the crew in order to ensure the satisfactory operation of the towing equipment, in particular the emergency quick-release systems, as requested by the operating manual.

Records of operational tests are should be kept on board and made available to Lloyd’s Register upon request.

2.2.7 Design requirements for towline guiding fittings

In addition, towline guiding fittings used for guiding the towline when towing on a towing winch must be able to sustain the force exerted by the towline loaded under a tension equal to the BHL of the associated winch in the most unfavourable anticipated position of the towline without exceeding the above-mentioned stress level criteria.

Finally, where a towline guiding fitting (e.g. fairlead or guide pin) has been designed for a specific Safe Working Load (SWL), defined as the maximum static working load, the fitting should be able to sustain a force equal to 2 times the SWL without exceeding the above-mentioned stress level criteria.

2.2.8 Additional design guidance for towline guiding fittings

In addition to the Rule requirements outlined in Ch 2, 2.2 Towing arrangements for Tugs 2.2.7, the following design guidelines should be followed.

When considering the above design checks for the strength of towline guiding fittings, at the discretion Lloyd’s Register, where the yielding check of the towline guiding fittings is carried out by means of a three-dimensional finite element model, an increase of the permissible stress levels given above by 10 per cent (compared to a beam model) will be specially considered.

Sizing and radiusing of towline guiding fittings should be appropriate to prevent fretting or abrasion of any towlines.

All towline guiding fittings should be regularly checked and maintained to ensure their condition does not affect smooth carriage of the towline.

The placement of towline guiding fittings should be such that they do not cause undue friction or bending beyond the specified limits of the towline manufacture.

Adequate towline guiding fittings should be supplied and arranged to effectively lead and restrain the towline within the designed limits of its sweep.

Towing guiding fittings should generally be arranged in such a position (noting the position of towing equipment and towline path) as to minimise heeling moment due to the towline force.

2.2.9 Design requirements for towing hooks

The classification Rules require that towing hooks and their load carrying attachments (connecting the towing hook to the hull structure) must be able to sustain the DL without exceeding an equivalent stress level (based on von Mises criterion) of 0.80σ_y.

The supporting calculations to demonstrate this are to be provided to Lloyds Register and must consider the DL being applied in the most unfavourable anticipated position for the structure.

2.2.10 Additional design guidance for towing hooks

In addition to the mandatory Rule requirements the following additional guidance should be complied with.

Towing hooks should be provided with an emergency quick-release device operable from a position on the bridge with full view and control of the towing operation, as well as at a location near the hook where the device can be safely operated. Identical means of control for the emergency quick-release devices should be provided at each control station and are to be protected against unintentional use.

The force necessary to open the hook under load should not be greater than 150 N.

The applicable procedures for the emergency quick-release device should be communicated to the crew and vital information should be displayed next to the control desk or another appropriate location.

Towing hooks should generally be arranged in such a position (noting the position of towline guiding fittings and towline path) as to minimise heeling moment due to the towline force.

2.2.11 Guidelines on testing of towing hooks

The following guidelines outline the appropriate testing regimes for towing hooks installed on board tugs.

Towing hooks, including the associated emergency quick-release devices, should be load tested to the DL, as defined in Ch 2, 2.2 Towing arrangements for Tugs 2.2.3, at a specialised facility equipped to generate the required line tension (e.g. maker’s premises) and witnessed by Lloyd’s Register.

In case a towing hook is of conventional, proven design, for which load testing has been previously performed in a manner deemed acceptable by Lloyd’s Register, (evidence and results of load testing should be supplied), it may be sufficient to perform on board function testing in accordance with the guidelines specified below.

The proper functioning of the towing equipment should be verified by on board testing witnessed by Lloyd’s Register. Function testing should be performed both for normal operating conditions in accordance with the towing arrangement plan (see Ch 2, 2.2 Towing arrangements for Tugs 2.2.2) and for emergency conditions (emergency quick-release, failure of main power supply). The safe operation of the towing hook from all control stations should be demonstrated.

Towing hooks should be function tested on board. The correct functioning of the hook and the associated supporting structure should be demonstrated at a towline force equal to the bollard pull, as defined in Ch 1, 1.3 Definitions 1.3.1. The emergency quick-release should be function tested under normal power supply conditions with a towline force corresponding to the minimum thrust (engine(s) clutched in and running at idle speed), as well as in a dead-ship condition (without strain in the towline).

Operational tests should be performed by the crew in order to ensure the satisfactory operation of the towing equipment, in particular the emergency quick-release systems, as requested by the operating manual.

Records of operational tests are should be kept on board and made available to Lloyd’s Register upon request.

2.2.12 Design requirements for towing equipment supporting structures

In addition, the supporting structures of towing equipment engaged for escort operations or when towing on a towing winch must be able to sustain the load exerted on the supporting structure under the action of the towline loaded under a tension equal to the BHL of the associated winch, as specified in Ch 1, 1.3 Definitions 1.3.5, in the most unfavourable anticipated position of the towline without exceeding the stress level criteria specified above.

Also, where a towline guiding fitting has been designed for a specific SWL, defined as the maximum static working load, the associated supporting structure should be able to sustain a force equal to 2 times the SWL without exceeding the stress level criteria specified above.

2.2.13 Additional design guidelines for towing equipment supporting structure

In case the yielding check of the towing equipment supporting structures is carried out by means of a threedimensional finite element model, increase of the permissible stress levels given above by 10 per cent (compared to a beam model) will be specially considered by Lloyd’s Register.

Care should be taken that if towing equipment supporting structure is also exposed to other loads (e.g. weather deck loadings ) in combination with the with loads from towing, then these additional loads should be superimposed into the strength assessment in order to produce the most conservative case for analysis.

2.2.14 Additional design guidelines for winch emergency release systems

The emergency release system should be operable under all normal and reasonably foreseeable abnormal conditions (these may include, but are not limited to, the following: vessel electrical failure, extreme list/trim angles, load applied at the limits of operating load, fleet angle, variable load (for example due to heavy weather), etc.).

Emergency release systems should allow the winch drum to rotate and allow the towline to pay out in a controlled manner.

An alternative source of energy should also be provided such that normal operation of the emergency release system can be sustained under dead-ship conditions for at least three complete emergency release system operations of the most demanding winch connected to it.

Where the winch design is such that the brake is applied by spring tension and released using hydraulic or pneumatic power, sufficient power should be provided to operate the emergency release system, in a dead-ship situation, for a minimum of five minutes. This may be reduced to the time required for the full length of the towline to feed off the winch drum at the minimum load as specified below if this is less than five minutes, noting that after the emergency release system has been activated it is considered good practice for the brake to first completely open and then automatically tighten slightly to ensure a controlled release of the towline.

The emergency release system should function as quickly as reasonably practicable and within a maximum of three seconds after activation.

Arrangements should ensure that when emergency release system is activated, there is sufficient resistance to rotation to avoid uncontrolled unwinding of the towline from the drum.

The emergency release system should be capable of operating at 100 per cent of the BHL of the associated winch.

Emergency release operation should be possible from the bridge and from the winch control station on deck. The winch control station on deck should also be in a safe location.

The emergency release control should be located in close proximity to the emergency stop button for winch operations and both should be clearly identifiable, clearly visible, and easily accessible and positioned to allow safe operability.

The emergency release function should take priority over any emergency stop function. Activation of the winch emergency stop from any location should also not inhibit operation of the emergency release system from any location.

Emergency release system control buttons are should be of the 'lock-in' type or require positive action to cancel.

Controls for emergency use should be protected against accidental use.

Wherever practicable, control of the emergency release system should be provided by a hard-wired system, fully independent of programmable electronic systems.

Programmable electronic systems that operate or may affect the control of emergency release systems should generally be considered as safety critical/ essential systems.

The emergency release system reset function should be always available from the bridge regardless of the activation location and without manual intervention on the working deck.

2.2.15 Guidelines on testing of winch emergency release systems

For each emergency release system or type thereof, should be verified either at the manufacturer's works or as part of the commissioning of the towing winch when it is installed on board. Where verification solely through testing is impractical (e.g. due to health and safety), testing may be combined with inspection, analysis or demonstration will be considered by Lloyd’s Register on a case-by-case basis.

The performance capabilities of the emergency release system should be documented and made available on board the ship on which the winch has been installed.

The full functionality of the emergency release system should be tested as part of the shipboard commissioning trials to the satisfaction of the Surveyor. Testing may be conducted either during a Bollard Pull test or by applying the towline load against a strong point on the deck of the tug that is certified to the appropriate load.

For novel designs the emergency release systems should also be load tested with the towline at an upward angle of 45 degrees with the horizontal plane at a towline force of not less than 50 per cent of the design bollard pull.

2.2.16 Design requirements for towlines

The design requirements for towlines are contained within Table 13.7.1 Equipment requirements in Pt 3, Ch 13, 7 Equipment of the Rules and Regulations for the Classification of Ships, July 2022.

2.2.17 Additional design guidelines for towlines

In addition to the Classification Rule requirements the following design guidelines should be followed.

The breaking strength of towlines should be in accordance with appropriate industry standards for marine operations, but not less than the appropriate DL.

In addition, the breaking strength of towlines used on a towing winch should not be less than the BHL of the associated winch (see Ch 1, 1.3 Definitions 1.3.5).

The towline should be protected from being damaged by chafing and abrasion. To this end cargo rails, bulwarks, and other elements, supporting the towline should be sufficiently rounded with consideration to the bend radius limit of the towline in order to ensure that that the towline breaking strength is maintained.

The total length of the towline applied on a towing winch is to be such that under normal operation at least half a layer remains on the drum. In no case should less than three turns remain on the drum during normal operation.

2.3.1 The Rule requirements relating to the towing equipment and their foundations are contained within Pt 4, Ch 3, 7 Towing arrangements of The Rules and Regulations for the Classification of Ships, July 2022.

2.3.2 Materials used in towing equipment should comply with the applicable class requirements for materials. Class certificates are generally required for the materials used for winch drums, drum shafts, winch brake components, winch supporting frames, towing hooks and towline guiding fittings installed upon classed vessels.

2.3.3 The guidelines outlined in Ch 2, 2.2 Towing arrangements for Tugs are also applicable to Escort tugs in relation to normal towing services i.e. towing and pushing operations other than escorting as defined in Ch 1, 2.1 Typical tug operational profiles 2.1.4.

2.3.4 Documents to be submitted

Additionally, where deemed necessary by Lloyd’s Register, buckling and/or fatigue analysis, performed in accordance with a standard or code of practice recognised by Lloyd’s Register, may be required to be submitted for information.

In case the final values are not yet available, estimated values may be submitted as preliminary information for the purposes of an initial design review. In case the discrepancy between the final values and the preliminary values, the drawings may need to be re-reviewed against the final values.

2.3.5 Consideration of the design load

The DL (in the Rules and in the table) take into consideration the assumed dynamic effects through the application of the dynamic amplification factor (DAF) which is clearly designated in square brackets in Table 2.2.3 Design loads: escort tug (see also Ch 1, 1.3 Definitions 1.3.4).

2.3.6 Design requirements for escort winches

The Rules require that the scantlings for escort winches (including winch drums, drum shafts, brakes, support frames and connections to the hull structure) are to be determined by direct calculations using the Design Loads (outlined in Table 2.2.3 Design loads: escort tug)

2.3.7 Additional design guidance for escort winches

In addition to the Rule requirements outlined in Ch 2, 2.3 Towing arrangements for Escort Tugs 2.3.6, the following design guidelines should be followed.

Winches should be provided with an emergency quick-release device operable from a position on the bridge with full view and control of the towing operation. Means of control for the emergency quick-release device should be protected against unintentional use.

Escort winches should generally be arranged in such a position (noting the position of towline guiding fittings and towline path) as to minimise heeling moment due to the towline force.

The winch brake should normally act directly on the drum and should be operable (either manually or otherwise) in case of failure of the primary power supply system.

The dimensioning of the winch drum should take into account the rope bending specifications provided by the towline manufacturer.

Due consideration should be given to preventing the towline slipping over the flanges of the drum.

Escort winches intended to be used in conditions where dynamic oscillations of the towline are likely to occur, such as in open sea areas or other areas exposed to waves, should be equipped with an active pay-out and haul-in system. This system should automatically and reliably pay-out the towline in a controlled manner when the towline force exceeds a 23 pre-set (adjustable) level equal to 110 per cent of the rated towline force F_t,R ,and as the towline force is reduced, actively haul-in the towline to prevent slack-line events thereby maintaining a pre-set or adjustable towline force consistent with the rated towline force.

Pay-out and haul-in speeds and pull capability should be chosen taking into account the anticipated escort services and the dynamic characteristics of the escort tug.

Escort operations in conditions where dynamic oscillations of the towline are likely to occur should not be based on the use of the brakes of the winch drum.

Escort operations performed by escort tugs with the service restriction notation protected waters and any escort operation in calm water conditions, such as in ports and sheltered waters, may be based on the use of the brakes of the winch drum. As a minimum, the winch brake holding load (BHL) should be equal to or greater than two times the maximum steady towline force F_t,MAX.

Escort winches should be fitted with equipment to continuously measure the tension in the towline. The measured data should be displayed in the wheelhouse next to the control desk or another appropriate location.

The escort towing system should be designed so as to enable the proper spooling of the towline when hauling in. Generally this can be achieved by a suitable design of the fairlead or staple guiding the towline between the escort winch and the assisted ship.

Where a spooling device is fitted, it should be designed for the same design load and stress criteria as the towline guiding fittings, see Ch 2, 2.2 Towing arrangements for Tugs 2.2.7.

2.3.8 Guidelines on testing of escort winches

The following guidelines outline the appropriate testing regimes for escort winches installed on board escort tugs.

Escort winches, including the associated emergency quick-release device should generally be load tested to the DL, as defined in Ch 2, 2.2 Towing arrangements for Tugs 2.2.5, or the BHL, as defined in Ch 1, 1.3 Definitions 1.3.5, whichever is the greatest. Generally, load testing should be conducted at a specialised facility equipped to generate the required line tension (e.g. maker’s premises) and witnessed by Lloyd’s Register.

In case an escort winch is of conventional, proven design, for which load testing has been previously performed in a manner deemed acceptable by Lloyd’s Register (evidence and results of load testing should be supplied), it may be sufficient to perform on board function testing in accordance with the requirements specified below.

The proper functioning of the towing equipment used for escort services should be verified by on board testing witnessed by Lloyd’s Register. Function testing should be performed both for normal operating conditions in accordance with the escort towing arrangement plan, seeCh 2, 2.3 Towing arrangements for Escort Tugs 2.3.4, and for in emergency conditions (emergency quick-release, failure of main power supply). The safe operation of the escort winch from all control stations should be demonstrated.

Escort winches should be function tested on board. The correct functioning of the winch brake, the load carrying winch components and the associated supporting structure should be demonstrated at a towline force equal to the bollard pull, as defined in Ch 1, 1.3 Definitions 1.3.1. The emergency quick-release should be function tested under normal power supply conditions with a towline force corresponding to the minimum thrust (engine(s) clutched in and running at idle speed), as well as in a dead-ship condition (without strain in the towline).

Winch operating modes which should be function tested include hauling in and paying out of the towline, braking and the active pay-out and haul-in system when fitted.

Hydraulic and electrical systems should be function tested on board in accordance with Lloyd’s Register’s requirements for machinery and electrical systems.

Operational tests should be performed by the crew in order to ensure the satisfactory operation of the towing equipment used for escort services, in particular the emergency quick-release systems, as requested by the operating manual.

Records of operational tests should be kept on board and made available to Lloyd’s Register upon request.

2.3.9 Design requirements for towline guiding fittings

In addition, towline guiding fittings should be able to sustain the force exerted by the towline loaded under a tension equal to the BHL of the associated winch in the most unfavourable anticipated position of the towline without exceeding the above-mentioned stress level criteria

Finally, where a towline guiding fitting has been designed for a specific Safe Working Load (SWL), defined as the maximum static working load, the fitting should be able to sustain a force equal to 2 times the SWL without exceeding the above-mentioned stress level criteria.

2.3.10 Additional design guidance for towline guiding fittings

In addition to the Rule requirements out lined in Ch 2, 2.2 Towing arrangements for Tugs 2.2.7, the following design guidelines should be followed.

When considering the aforementioned design checks for the strength of towline guiding fittings, at the discretion Lloyd’s Register, where the yielding check of the towline guiding fittings is carried out by means of a three-dimensional finite element model, an increase of the permissible stress levels given above by 10 per cent (compared to a beam model) will be specially considered.

Sizing and radiusing of towline guiding fittings should be appropriate to prevent fretting or abrasion of any towlines.

All towline guiding fittings should be regularly checked and maintained to ensure their condition does not affect smooth carriage of the towline.

The placement of towline guiding fittings should be such that they do not cause undue friction or bending beyond the specified limits of the towline manufacture.

Adequate towline guiding fittings should be supplied and arranged to effectively lead and restrain the towline within the designed limits of its sweep.

2.3.11 Design requirements for towing equipment supporting structures

In addition, the supporting structures of towing equipment engaged for escort operations must be able to sustain the load exerted on the supporting structure under the action of the towline loaded under a tension equal to the BHL of the associated winch, as specified in Ch 1, 1.3 Definitions 1.3.5, in the most unfavourable anticipated position of the towline without exceeding the stress level criteria specified above.

Also, where a towline guiding fitting has been designed for a specific SWL, defined as the maximum static working load, the associated supporting structure should be able to sustain a force equal to 2 times the SWL without exceeding the stress level criteria specified above.

2.3.12 Additional design guidelines for towing equipment supporting structure

In case the yielding check of the towing equipment supporting structures is carried out by means of a threedimensional finite element model, increase of the permissible stress levels given above by 10 per cent (compared to a beam model) will be specially considered by Lloyd’s Register.

Care should be taken that if towing equipment supporting structure is also exposed to other loads (e.g. weather deck loadings ) in combination with the with loads from towing, then these additional loads should be superimposed into the strength assessment in order to produce the most conservative case for analysis.

2.3.13 Additional design guidelines for winch emergency quick-release systems

The emergency quick-release device should be capable of releasing the towline under the maximum anticipated load regardless of the angle of the towline and the tug’s trim and heel. This device should be operable from a position on the bridge with full view and control of the towing operation.

The emergency quick- release system should be operable under all normal and reasonably foreseeable abnormal conditions (these may include, but are not limited to, the following: vessel electrical failure, extreme list/trim angles, load applied at the limits of operating load, high fleet angle, variable load (for example due to heavy weather), etc.).

Means of control for the emergency quick-release device should be protected against unintentional use.

The time delay between the initiation and actual start of the emergency quick-release (pay-out of the towline) should be as short as reasonably practicable.

The speed of paying out should be such that the tension in the towline is reduced as fast as reasonably possible, taking into consideration that paying out should be in a controlled manner. To that end effective means to prevent spinning (free, uncontrolled rotation) of the winch drum should to be provided as spinning of the winch drum could cause the towline to get stuck and disable the release function of the winch.

After a quick-release event the winch brakes should be able to operate normally (automatically), while the winch motor should be engaged manually (not automatically).

The applicable procedures for the emergency quick-release device, including time delays and release speed, should be communicated to the crew and such vital information should be displayed next to the control desk or another appropriate location.

2.3.14 Guidelines on testing of winch emergency release systems

For each emergency release system or type thereof, should be verified either at the manufacturer's works or as part of the commissioning of the escort winch when it is installed on board. Where verification solely through testing is impractical (e.g. due to health and safety), testing may be combined with inspection, analysis or demonstration will be considered by Lloyd’s Register on a case-by-case basis.

The performance capabilities of the emergency release system should be documented and made available on board the ship on which the winch has been installed.

The full functionality of the emergency release system should be tested as part of the shipboard commissioning trials to the satisfaction of the Surveyor. Testing may be conducted either during a Bollard Pull test or by applying the towline load against a strong point on the deck of the tug that is certified to the appropriate load.

For novel designs the emergency release systems should also be load tested with the towline at an upward angle of 45 degrees with the horizontal plane at a towline force of not less than 50 per cent of the design bollard pull.

2.3.15 Design requirements for towlines

The design requirements for towlines are contained within Table 13.7.1 Equipment requirements in Pt 3, Ch 13, 7 Equipment and Pt 4, Ch 3, 9.2 Towing arrangements 9.2.1 of the Rules and Regulations for the Classification of Ships, July 2022.

2.3.16 Additional design guidelines for towlines

In addition to the Classification Rule requirements the following design guidelines should be followed.

The breaking strength of towlines should be in accordance with appropriate industry standards for marine operations, but not less than the appropriate DL.

In addition, the breaking strength for towlines used for escort services on an escort winch should not be less than the BHL of the associated winch (see Ch 1, 1.3 Definitions 1.3.5)

The towline should be protected from being damaged by chafing and abrasion. To this end cargo rails, bulwarks, and other elements, supporting the towline should be sufficiently rounded with consideration to the bend radius limit of the towline in order to ensure that that the towline breaking strength is maintained.

It is recommended that the total length of the towline applied on a towing winch is to be such that under normal operation at least half a layer remains on the drum. In no case should less than three turns remain on the drum during normal operation.

2.3.17 Additional recommended equipment for Escort tugs

Escort tugs should be equipped with a calibrated heeling angle measurement system (inclinometer).

The measured heeling angle should be displayed in the wheelhouse next to the control desk or another appropriate location where the readout is prominent.

2.4.1 The Rule requirements relating to the tug fendering are contained within Pt 4, Ch 3, 8 Fenders of The Rules and Regulations for the Classification of Ships, July 2022.

2.4.2 Design requirements for Fenders

The Rules stipulate that ‘An efficient fender is to be fitted to the ship's side at deck level extending all fore and aft’.

2.4.3 Additional design guidelines for Fenders

The following additional guidance should be applied with respect to the fendering arrangements for tugs.

A robust and efficient fendering system should be fitted in all areas intended for pushing. The purpose of the fendering system is to distribute the pushing force and limit its dynamic component on the hull structure of both the tug and the assisted ship.

The design of the fendering system, in particular the contact area and stiffness distribution, should result in an acceptable pressure distribution on the supporting structure of the tug (and the assisted ship) under the maximum anticipated loads during pushing operations.

The DL takes into consideration anticipated dynamic effects through the application of the DAF (designated in square brackets in the formula) in but not bouncing effects.

Note, within the context of this guidance note, it is considered that during pushing operations the contact between the tug and assisted ship is maintained and that no bouncing (e.g. under wave action) is taking place as it is understood that pushing operations are normally halted when bouncing starts to occur due to operational difficulties in keeping position within the pushing area of the assisted ship as well as controlling the associated impact type loads.

Therefore forces resulting from bouncing loads are not considered, if this assumption is not valid for the design and the operational profile of the vessel then these dynamic forces are should be included in any fendering calculations. Calculations of the additional forces and their application to the design should be forwarded to Lloyd’s Register at the earliest possible convenience for timely consideration.

2.5.1 For Escort tugs, Lloyd’s Register offers the specific notations EPN (F,B,V,C) and CFD EPN (F,B,V) to denote the escort performance numeral of the vessel. In the case of EPN the escort performance numeral is obtained by full scale testing and for CFD EPN it is obtained through CFD.

Where escort performance numerals are predicted using computational fluid dynamics, the escort performance numeral ‘C’ is omitted

2.5.2 Rules references and guidance

The EPN notation is described in Pt 1, Ch 2, 2.3 Class notations (hull) 2.3.21 of the Rules and Regulations for the Classification of Ships, July 2022.

The EPN trial requirements are detailed in Pt 4, Ch 3, 9.3 Performance numeral and trials of the Rules and Regulations for the Classification of Ships, July 2022.

The CFD EPN requirements are detailed in Pt 4, Ch 3, 9.4 Computational Fluid Dynamics Predicted Performance of the Rules and Regulations for the Classification of Ships, July 2022. Further details on the suitable calculation of EPN through CFD are detailed in the Lloyd’s Register ShipRight Procedure titled Guidelines for CFD Escort Tug Performance.

2.6.1 Design requirements for Anchoring Equipment

The Classification requirements for anchoring equipment are governed by the equipment number for the vessel. For tugs this is calculated in as detailed in Pt 3, Ch 1, 7.1 Calculation of Equipment Number 7.1.6 of the Rules and Regulations for the Classification of Ships, July 2022.

Having calculated the vessels equipment number and in order to be entitle the vessel to the figure 1 in its character of classification, equipment is to be provided in accordance with the requirements of Table 13.7.1 Equipment requirements of the Rules and Regulations for the Classification of Ships, July 2022.

The requirements of the table vary depending on any service restrictions associated with the vessel.

Attention is also drawn to Pt 3, Ch 13, 7.1 General 7.1.2 of the Rules and Regulations for the Classification of Ships, July 2022 which permits equipment differing from that listed if it is considered suitable go the particular service on which the ship is engaged.

Anchors are to be of an approved design and the mass and number of anchors, length of wire rope or chain are to be in compliance with the requirements outlined in the aforementioned table.

2.6.2 Additional design guidelines for anchors

The design of all anchor heads should be such so as to minimise stress concentrations, and in particular, the radii on all parts of cast anchor heads should be as large as possible, especially where there is considerable change of section.

Anchors which must be specially laid the right way up, or which require the fluke angle or profile to be adjusted for varying types of sea bed, will not generally be considered for normal ship use.

The number of anchors and chain cables which should be carried should generally be in line with the aforementioned Table 13.7.1 Equipment requirements of the Rules and Regulations for the Classification of Ships, July 2022. However for vessels with the type notation tug which are limited to operations within protected waters or extended protected waters Lloyd’s Register will specially consider a reducing the required number of required anchors and chain cables to 1.

Lloyds Register may further specially consider a reduction of the number of anchors and chain cables as depicted in Table 2.2.5 Reduced number of anchors and chain cables based on redundancy principles. Basis of this consideration will be the service and operational restrictions of the vessel and the levels of redundancy on board, for example:

Lloyd’s register will specially consider the case where a spare anchor is supplied as an alternative to a second bower anchor. In such cases special provisions, such as a crane and suitable storage space for the spare anchor, should be present on board.

For tugs with a service restriction notation denoting that they are restricted to operations within protected waters or extended protected waters, effectively operating in a fixed and limited area, Lloyd’s Register will specially consider the case that the spare anchor is stored ashore.

2.7.1 All mechanical and Electrotechnical systems are to be in compliance with the relevant requirements within the Rules.

Which Rules are applicable to the vessel is dependent on the mechanical and electrical outfit of the vessel.

2.8.1 The requirements for Fire protection, detection and extinction are contained within Pt 6, Ch 4 Fire Protection, Detection and Extinction Requirements of the Rules and Regulations for the Classification of Ships, July 2022.

2.8.2 Both the Class Rules and statute stipulate that tugs of 500 gross tons or more, on international voyages, where provision is made within International Conventions, are to be provided with the fire safety measures required by the International Convention for the Safety of Life at Sea, 1974, as amended.

In addition, the Class Rules stipulate that tugs of 500 gross tons or more employed on national voyages are to comply with the fire safety measures prescribed and approved by the Government of the Flag State.

2.8.3 For tugs of less than 500 gross tons The Rules and Regulations for the Classification of Ships, July 2022 also contain relevant requirements in Pt 6, Ch 4, 2 Fire detection, protection and extinction. The content of this section is within the spirit of the International Convention and Protocol requirements for ships of Convention size. However it is to be noted that the content of this section are “intended to apply to new and, as far as reasonable and practicable, or as found necessary by the relevant Administration, to existing cargo ships of less than 500 GT.”. As such, consideration will be given to the acceptance of fire safety measures prescribed and approved by the Government of the Flag State instead.

Ch 3, 3.1 Fire safety for tugs of less than 500 GT of this document includes Lloyd’s Register supported fire protection, detection and extinction minimum standard guidance.