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Fishing vessel stability

AMSA 507
26 February 2018

Stability is the force of buoyancy from the underwater parts of a vessel combined with the weight of its hull, equipment, fuel stores and load. These forces are affected by changing weather conditions and ocean swell. The stability of your vessel changes throughout your trip.

You must load your vessel evenly without overloading it. Stability is unique to each vessel and its operations.

To maintain correct stability of your vessel, you must:

  • plan and prepare your load properly before your trip
  • make changes and take corrective action throughout your trip.

Hazards to look out for

A major hazard must be identified in your vessel's safety management system including what measures are in place to avoid or reduce the risk of instability.

These are some common hazards which can lead to instability and how you can avoid them:

Modifying a vessel or installing new fishing gear

Additional or heavier equipment may affect and change the stability of your vessel. Any previous stability assessment you had conducted may also not be valid.

If you want to make modifications to your vessel contact us, your recognised organisation, or an accredited marine surveyor.

Overloading

You can overload your vessel by:

  • loading too much catch in hold
  • loading extra catch on the deck
  • carrying too much fishing equipment.

Work out how much catch you can safely carry and leave plenty of safety margin for weather, fuel and depth changes.

Reducing water on deck

Avoid collisions where breaking waves or ocean swells could cause water on deck.

A deck full of water is often the first stage in a capsize. A wave on deck drops tonnes of water weight which converts to a strong rolling force due to free-surface effects.

Accidental flooding

Valves and leaks in the engine space or down flooding through hatches doors and vents can introduce a hazard that no one notices.

To avoid this, make sure:

  • bilge alarms and pumps are working
  • doors and hatches closed and free from obstructions.

Secure fishing gear and your load

Stow your vessel's load, gear or catch:

  • on the centreline
  • balanced evenly across port and starboard
  • as low as possible. 

Secure your load so that it can withstand wave impact, rolling and wind loading without shifting.

Stabilisers

Stabilisers do not necessarily provide added stability—they only slow the rolling motion of the vessel.

Stabilisers can be major hazards when:

  • lowering, lifting or manoeuvring the arms
  • and deploying and recovering the plate or lifting surface.

These hazards must be planned for and in the vessel's safety management system.

Trawling, dredging and towing

If your vessel is overloaded or travelling in rough seas, you increase the risk of the following:

  • tow-line tension pulling the stern lower in the water, reducing the freeboard aft
  • the load’s downward weight taking the vessel lower in the water
  • tension on the lines transferred through the towing point or blocks lifting the vessel’s centre of gravity.

You can avoid this before the starting each tow or trawl by:

  • considering the ocean currents and swell direction
  • make sure the tow point is as low as possible.

Contact us, your registered organisation or an accredited marine surveyor before modifying the tow-point position.

Fouling or snagging fishing gear

Fouling or snagging fishing gear cause dangerous stability hazards, including:

  • reduced freeboard
  • steep angles and rolling forces from tension on the lines.

Be careful when trying to free fishing gear because of the load and stability changes of your vessel.

Lifting and pulling on board

A vessel's centre of gravity changes when you are lifting a catch using a winch or block. This can make the vessel unstable.

When lifting, consider:

  • your load—don't lift too much
  • the condition of the vessel
  • the ocean swell size and direction.

Author 

Australian Maritime Safety Authority

Documents 

Last updated: 24 April 2018
Last reviewed: 24 April 2018