ISO 13798:2020

Ships and marine technology - Ship's mooring and towing fittings - Recessed bitts (steel plate type)

This document specifies the types, nominal sizes, dimensions and materials, as well as construction, manufacturing and marking requirements, for steel plate type recessed bitts to meet normal towing requirements.

Navires et technologie maritime — Corps-morts et ferrures de remorquage de navires — Bittes d'amarrage encastrées (type plaques d'acier)

General Information

• Status: Published
• Publication Date: 27-Aug-2020
• ICS: 47.020.50 - Deck equipment and installations
• Technical Committee: ISO/TC 8/SC 4 - Outfitting and deck machinery
• Drafting Committee: ISO/TC 8/SC 4/WG 4 - Ship's mooring and towing fittings
• Current Stage: 9060 - Close of review
• Completion Date: 04-Mar-2031

Relations

• Revises: ISO 13798:2012 - Ships and marine technology - Ship's mooring and towing fittings - Recessed bitts (Steel plate type)
• Effective Date: 30-Sep-2017

Overview

ISO 13798:2020 - Ships and marine technology: Ship's mooring and towing fittings - Recessed bitts (steel plate type) defines requirements for steel plate type recessed bitts, the recessed mooring/towing fittings installed in a ship’s side shell where deck height makes conventional bitts impractical. The standard covers classification, nominal sizes, dimensions, materials, construction, manufacturing/inspection and marking to meet normal towing requirements.

Key topics and technical requirements

• Types & nominal sizes: Two manufacturing types - Type A (steel pipe) and Type B (steel plate). Nominal post diameters include 200, 250, 400A and 400B. Detailed dimensions and particulars are provided in the standard’s Table 1 and Figure 1.
• Materials: Type B uses weldable steel plates with yield ≥ 235 N/mm²; Type A uses weldable steel pipes with yield ≥ 215 N/mm².
• Strength assessment (Annex A): Strength is evaluated by simple beam theory. Load cases consider combined bending and shear from a towing force P at the upper position; reference rope diameters for load consideration are specified (e.g., 30, 35, 40, 60 mm depending on nominal size). Stress limits: bending ≤ 85% yield, shear ≤ 60% yield, combined ≤ 100% yield. A 2 mm wear allowance is deducted where rope rubs; corrosion margin is accounted for in stress criteria.
• Manufacturing & inspection: Surfaces (including welds) must be free of visible flaws; rope-contact surfaces must be smooth to avoid abrasion; external anti-corrosion coating is required.
• Marking & SWL: The Safe Working Load (SWL) must be noted in the shipboard towing and mooring plan (per IMO guidance) and permanently marked on the fitting (e.g., “SWL XXX t”). Actual on-board SWL must consider local reinforcement and shall not exceed the SWL in the standard.

Practical applications and users

ISO 13798:2020 is used for:

• Design and specification of recessed bitts during newbuild and retrofit work (naval architects, shipbuilders)
• Procurement and manufacturing of shipboard towing fittings (deck machinery manufacturers, fabricators)
• Survey, inspection and certification by classification societies and maritime authorities
• Ship operators and masters for safe mooring/towing planning and marking per IMO Circular MSC/Circ.1175

Practical benefits include consistent safety margins, reduced rope damage from well-designed recess boxes, and clear SWL marking to support safe towing and mooring operations.

Related standards

• IMO Circular MSC/Circ.1175 - Guidance on shipboard towing and mooring equipment
• ISO 2408 - Steel wire ropes - Requirements
• IACS UR A2 - Shipboard fittings and supporting hull structures associated with towing and mooring
• OCIMF Mooring Equipment Guidelines (MEG)

Keywords: ISO 13798:2020, recessed bitts, ship mooring, towing fittings, steel plate type, SWL, strength assessment, maritime equipment.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 13798
Second edition
2020-08
Ships and marine technology —
Ship's mooring and towing fittings —
Recessed bitts (steel plate type)
Navires et technologie maritime — Corps-morts et ferrures de
remorquage de navires — Bittes d'amarrage encastrées (type plaques
d'acier)
Reference number
©
ISO 2020
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
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Published in Switzerland
ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Classification . 1
4.1 Type . 1
4.2 Nominal sizes . 1
5 Dimensions . 2
6 Materials . 2
7 Construction . 2
8 Manufacturing and inspection . 2
9 Marking . 2
Annex A (normative) Basis for strength assessment of recessed bitts (steel plate type) .4
Bibliography . 6
Foreword
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This document was prepared Technical Committee ISO/TC 8, Ships and marine technology, Subcommittee
SC 4, Outfitting and deck machinery.
This second edition cancels and replaces the first edition (ISO 13798:2012), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— the definition of SWL (3.1) has been reworded;
— the leader line in Figure 1 has been amended.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved

Introduction
The recessed bitt is a type of ship’s towing fitting installed on the side shell of the ship.
Recessed bitts are normally provided to easily attach the towing lines where the height of the mooring
deck is too high.
...