Section 4 Guidance on non-convention cases
Clasification Society 2024 - Version 9.40
Clasifications Register Guidance Information - Guidance Note on the Required Lengths for Double Bottoms of Special Service Craft, October 2017 - Chapter 1 Guidance note on the required lengths for double bottoms of Special Service Craft - Section 4 Guidance on non-convention cases

Section 4 Guidance on non-convention cases

Parent topic: Chapter 1 Guidance note on the required lengths for double bottoms of Special Service Craft

4.1 LR recommended practice

4.1.1 As has been highlighted in the preceding Sections, there are scenarios where no double bottom requirements will be applicable for an SSC vessel. In such cases, LR recommends that the practices outlined in this Section (based on craft Rule length (LR)) are followed. These recommendations do not supersede any other Flag State or IMO instruments. For reference, Table 1.4.1 LR recommended practice reference is provided.

4.1.2 Where LR > 50 m, a double bottom should be fitted in the hull (or hulls in multi-hull craft), extending from the collision bulkhead to the forward watertight bulkhead for the machinery space.

4.1.3 Where 61 m < LR < 80 m, a double bottom should be fitted outside the machinery space and is to extend to the collision bulkhead and the aft peak bulkhead. Where no aft peak bulkhead is fitted, the extent of the double bottom should be as far aft as is practicable.

4.1.4 Where LR ≥ 80 m, SOLAS requirements are to be applied.

4.1.5 It is recommended that where the vessel is not complying with the above-mentioned double bottom arrangements, the design is subject to a damage survivability assessment. This check should consist of applying SOLAS bottom damages as detailed in SOLAS Ch. II-1 Reg. 9.8.2, and ensuring that none of the stipulated damage scenarios results in:
  • the margin line of the vessel being immersed at any point along its length (wave action need not be considered);
  • flooding of spaces responsible for providing emergency power and lighting, internal communication, signals or other emergency devices;
  • rendering emergency power and lighting, internal communication, signals or other emergency devices inoperable in other parts of the vessel.

The results of any such damage investigation should be provided to LR for consideration at the Plan Approval stage.

4.1.6 In all cases, the relevant Flag State should be consulted to ensure that the proposed arrangements are acceptable to them. Evidence of such acceptance is to be provided to LR for consideration at the Plan Approval stage.

Table 1.4.1 LR recommended practice reference

Vessel Rule Length LR (m) LR recommended DB length LR recommended survivability assessment if recommended DB is not fitted (See Note 1)
LR ≤ 50 m - At the Owner’s, Builder’s or Surveyor’s discretion, a survivability assessment (as detailed in Ch 1, 4.1 LR recommended practice 4.1.5).
50 m < LR ≤ 61 m As Ch 1, 4.1 LR recommended practice 4.1.2 ‘from the collision bulkhead to the forward watertight bulkhead for the machinery space’ A survivability assessment (as detailed in Ch 1, 4.1 LR recommended practice 4.1.5).
61 m < LR < 80 m As Ch 1, 4.1 LR recommended practice 4.1.3 ‘outside the machinery space and is to extend to the collision bulkhead and the aft peak bulkhead’ A survivability assessment (as detailed in Ch 1, 4.1 LR recommended practice 4.1.5).
LR ≥ 80 m SOLAS Ch.II-1 Reg. 9: ‘A double bottom shall be fitted extending from the collision bulkhead to the afterpeak bulkhead, as far as this is practicable and compatible with the design and proper working of the ship.’ SOLAS Ch. II-1 Reg. 9 Damages and damage stability criteria
Note 1. To be prepared by the Designer, Owner or Builder and submitted to LR for consideration.
Copyright 2022 Clasifications Register Group Limited, International Maritime Organization, International Labour Organization or Maritime and Coastguard Agency. All rights reserved. Clasifications Register Group Limited, its affiliates and subsidiaries and their respective officers, employees or agents are, individually and collectively, referred to in this clause as 'Clasifications Register'. Clasifications Register assumes no responsibility and shall not be liable to any person for any loss, damage or expense caused by reliance on the information or advice in this document or howsoever provided, unless that person has signed a contract with the relevant Clasifications Register entity for the provision of this information or advice and in that case any responsibility or liability is exclusively on the terms and conditions set out in that contract.