November 2018: Safety of vessels that are fitted with hinged fins as anti-roll devices

This safety update is issued to raise awareness of the potential risk of using anti-roll devices that are fastened to the hull bilges with hinges.

This safety update is for

  • New Zealand ship owners, operators, masters and crew
  • Maritime NZ recognised surveyors
  • Maritime NZ maritime officers, investigators and technical advisors


Hinged fin anti-roll device

Hinged fin anti-roll devices have recently been installed on a number of fishing vessels. The hinged fin anti-roll device is used to prevent the boat from rolling while underway. The device is usually a tubular steel arm that extends from the side of the ship and into the water at right angles to the hull.

The device is fastened to the hull bilges with hinges. The purpose of the device is to reduce the vessel’s rolling motion when lowered. It is held in place in the working position by a vertical sliding arm.


Risk to safety

The hinged fin anti-roll devices may provide a more comfortable working platform by reducing the rolling motion, but they do not improve a vessel’s stability. In some circumstances, an anti-roll device can hide a deteriorating stability condition and provide a false sense of safety. A malfunction of the device may also create an immediate stability risk.

The design of the attachment point for the heel of the fin may affect the main structure of the vessel and its watertight integrity. Operators must ensure that the anti-roll fins are of a robust design and have gained design approval from their Maritime NZ recognised surveyor.

Possible risks of using this type of device include:

Hull damage

Hull damage may occur if the fin hits something while underway. The risk is higher on composite or wooden hull vessels. Hull damage may lead to sinking.

Sudden vessel heel

Damage to a fin or loss of a hinge may cause the fin to twist. If this occurs, particularly at speed, it may cause the vessel to heel sharply and suddenly. Crew may lose their footing and/or be thrown into objects or even overboard.

Reduced stability

The dragging effect of the fins may decrease vessel stability in heavy seas, increasing the risk of capsizing.

Loss of control

A twisted fin may suddenly turn the vessel abeam to the sea or affect the ability to steer in other ways.

Hazardous working practices

Repair or recovery of a damaged fin or sliding arm may require improvisation. This may lead to risk of injury to crew members.

Bar crossing

Making a bar crossing with a hinged fin deployed/down may be extremely dangerous. Broaching is always possible during a bar crossing. The fin could hinder the recovery of the vessel from the broaching situation. It could also lead to capsize.

Harbours and wharfs

Leaving fins deployed/down while in a harbour or alongside could cause danger to other vessels as the fins would be submerged and unseen.


What you should do

Check that the device has been custom designed and approved by a Naval Architect for structural strength and design.

Before installing the device, review the operating instructions and consider the risks carefully. Think about the effect the weight of the device will have on stability.

Make sure you understand how the device may affect your vessel. Think about the risks of using the device and consider if it makes sense for your operation.

Develop safe operating procedures and train the people who will be using the device to use it safely. Add the procedure to your operator plan and the training to your training schedule.

If you do install the device, or have already installed one, you as owner, master or operator, have legal responsibilities for vessel safety.

These include:

  • considering any risks and taking steps to eliminate or minimise them
  • ensuring the design has been approved and surveyed by a Maritime NZ recognised surveyor
  • having operating procedures in place so that the device is used safely
  • training the crew on how to use the device and making sure they understand the device’s operating limits so that they do not put the vessel in danger
  • ensuring crew follow the procedures and are aware of the risks.

Check with local harbour authority as to the use of the device when in harbour limits.


Further reading

Further information on vessel stability and the use of stabilisers is available from the following sources:

Vessel stability

Transport Canada - Ship Safety Bulletin No 04/2010 []

Original source content - Safety bulletin 39, November 2018: Safety of vessels that are fitted with hinged fins as anti-roll devices.


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