Common Structural Rules - Common Structural Rules for Bulk Carriers and Oil Tankers, January 2019 - Part 2 Ship Types - Chapter 2 Oil Tankers - Section 4 Hull Outfitting - 1 Supporting Structures For Components Used In Emergency Towing Arrangements
1 Supporting Structures For Components Used In Emergency Towing Arrangements
1.1 General
1.1.1
Emergency towing arrangements are to be fitted at both the bow and stern of every tanker with a deadweight of 20,000 tonnes or more, as required by SOLAS.
1.1.2
The design and construction of the towing arrangements is to be approved by the Flag Administration.
1.2 Documents to be submitted
1.2.1
Plans showing details of the supporting structure for the emergency towing arrangement, including the connection to the deck, are to be provided for approval. Information on emergency towing arrangement showing sufficient detail to enable the position and direction of load actions to be ascertained is to be submitted for reference.
1.3 Structural arrangement
1.3.1 Continuity of strength
The structural arrangement is to provide continuity of strength.
1.3.2 Stress concentrations
The structural arrangement of the ship’s structure in way of the emergency towing equipment is to be such that, abrupt changes of shape or section are to be avoided in order to minimise stress concentrations. Sharp corners and notches are to be avoided, especially in high stress areas.
1.4 Minimum thickness requirements
1.4.1 Deck plating
The deck in way of strong-points and fairleads is to have a minimum gross thickness of 15 mm.
1.5 Loads
1.5.1 Safe working loads
Safe working load of emergency towing arrangements is not to be taken less than:
- 1,000 kN for tankers having a deadweight greater than or equal to 20,000 t, but less than 50,000 t.
- 2,000 kN for tankers having a deadweight greater than or equal to 50,000 t.
1.5.2 Load case
The design load for the connection of the strong-point and fittings to the deck and its supporting structure is to be taken as twice the safe working load. Information on lines of action of the applied design load provided in emergency towing arrangement plan is to be taken into account.
1.6 Scantling requirements
1.6.1 General
The scantlings of the support structure are to be dimensioned to ensure that for the load cases specified in [1.5.2], the calculated stresses in the support structure do not exceed the permissible stress levels specified in [1.6.3].
The capacity of the structure to resist buckling failure is also to be assured.
1.6.2 Calculation procedure
These requirements are to be assessed using a simplified engineering analysis based on elastic beam theory, two dimensional grillage or finite element analysis using gross scantlings.
l.6.3 Permissible stresses
For the design load given in [1.5.2], the shear stresses and normal stresses, including bending stresses induced in the supporting structure and welds, in way of strong-points and fairleads, are not to be exceed the permissible values given below based on the gross thickness of the structure:
- Normal stress, 1.00 ReH.
- Shear stress, 0.58 ReH
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