Safety practices related to small fishing vessel stability


Safety practices related to small fishing vessel stability


Ari Gudmundsson
Fishery Industry Officer (Vessels)
Fishing Technology Service
Fish Products and Industry Division
FAO, Rome

Rome, 2009

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ISBN 978-92-5-106202-9

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FAO and UNEP 2009

Gudmundsson, A.
Safety practices related to small fishing vessel stability.
FAO Fisheries and AquacultureTechnical Paper;No. 517. Rome, FAO. 2009. 54p.


This document introduces some basic principles on the stability of small fishing vessels and provides simple guidance on what fishing vessel crews can do to maintain adequate stability for their vessels. It is not intended to be a complete course on fishing vessel stability The publication is aimed at fishers and their families, fishing vessel owners, boatbuilders, competent authorities and others who are interested in the safety of fishing vessels and fishers. It may also serve as a guide for those concerned with training in matters of safety of fishing vessels. It is recommended to translate and adapt the content for each target audience, in order to be consistent with the local weather conditions, types of vessels, fishing gear being used, etc.


Preparation of this document (Download pdf 568 kb)

1.  Introduction 

2.  Definitions (Download pdf 535 kb -pdf 426 kb - pdf348 kb - pdf767 kb)

     Light ship weight
     Displacement mass
     Centre of gravity
     Centre of buoyancy
     Transverse stability
     Why a fishing vessel remains upright
     Metacentric height
     Unstable equilibrium
     Neutral equilibrium
     Stiff and tender vessels
     Suspended weight
     Free surface effect
     Watertight and weathertight integrity
     Built-in buoyancy for undecked vessels
     Righting lever
     Stability curves (GZ curves)
     Dynamic stability
     Changes in the stability curve during the voyage

3.  Precautions (Download pdf 466 kb - pdf 603 kb)

     Enclosed superstructures and means of closing
     Securing of heavy material
     Stowage of the catch
     Effects of fishing gear on stability
     Free surface effects
     Following and quartering seas
     Crossing sand bars and beach landings
     Determining stability of small vessels with rolling period tests

4.  Alterations to vessels (Download pdf 102 kb)

5.  Stability criteria for small fishing vessels (Download pdf 78 kb)

6.  Stability documentation (Download pdf 446 kb)
     Stability notice
     Hydrostatic curves
     Cross curves
     Operating conditions
     Stability curve

7.  References (Download pdf 277 kb)

Annex 1 Examples of symbols used in stability documentation

Annex 2 Terms and symbols

Annex 3 Test on fishing vessel stability

Annex 4 Documentation consulted