November 1995: Stability of fishing boats and other small vessels carrying cargo or passengers

Background

A number of vessels have recently capsized and foundered with loss of life due to loss of stability.

Information on stability

Maritime New Zealand concluded that the loss of the boat was caused by a combination of unapproved modifications increasing the top weight of the boat, overloading, carrying fish too high in the boat, and the Skipper’s lack of knowledge of the stability characteristics of the boat. These combined factors resulted in the capsize and loss of the boat in conditions which the boat should normally have been expected to weather.

Safe practice tips

Loss of stability occurs for a number of reasons and in a variety of circumstances:

• Bad distribution of weight resulting in a vessel becoming top-heavy, e.g. large quantities of fish, craypots or cargo being stowed on deck, with little or no weight stowed below.
• The creation of a capsizing moment by attempting to clear crayfish pots and nets by hauling with the lifting gear.
• Use of the vessel's lifting gear for purposes other than those for which it was designed, e.g. swinging heavy weights over the side causing excessive heeling and possible capsize of the vessel.
• Water finding its way into the vessel or water being unable to escape from the deck.
• Partially filled fuel and water tanks, particularly in vessels with tanks extending from side to side.
• Overloading which reduces the vessel's reserve buoyancy and seriously affects stability.

The following points should be remembered to ensure the stability of your vessel:

1. Fishing gear, spare gear and any heavy weights including cargo should be properly stowed and secured. They should be placed as low down in the boat as possible and stowed uniformly about the centre line. On all occasions deck loads of fish should be kept as small as possible. The greatest possible amount of fish should be stowed in the hold or freezer to maintain a low centre of gravity.
2. Particular care should be taken when hauling catches and recovering heavy gear or when the trawl catches on an obstruction, as this may have an adverse effect on stability. Heavy weights suspended from lifting gear at sea should be secured to prevent them swinging from side to side.
3. Be careful when filling tanks at sea because slack tanks cause a rapid loss of stability. At any one time keep the number of partially filled tanks to a minimum, the aim being to have as many tanks as possible either completely full or empty. When the main deck is prepared for carrying a deck load by division with pond boards, there must be slots between them to allow easy flow of water to the freeing ports. Freeing ports provided with closing appliances should always be capable of functioning and should never be bolted or blocked off. Ensure that all portable divisions in the hold are in place before loading fish in bulk. Any fish on deck must be restrained from moving and arranged so that it does not cause the vessel to list.
4. In all conditions of loading, ensure that your boat has adequate freeboard (distance from main deck to water level). Make sure your boat is not overloaded with fish, cargo and/or passengers beyond the certified limits. This may seriously reduce your freeboard which, in turn, can mean more water on deck in the event of bad weather.
5. All doorways, hatchways, ports and other openings through which water can enter the hull or deckhouses must be properly closed while the boat is at sea and particularly in adverse weather conditions and all appliances for ensuring watertightness must be maintained in good condition.
6. In the case of fishing vessels, hatchcovers, doors and any ports should be kept properly closed when not in use during fishing.
7. During bad weather, secure all closing devices on vent pipes to fuel tanks and to spaces below the main deck.
8. If excessive or unusual heeling or yawing occurs, reduce speed and head into the sea as a first precaution.
9. Reliance on automatic or fixed steering is dangerous as this prevents speedy manoeuvring which may be required in bad weather.
10. Do not add top weight to your boat, e.g. by extending the size of the cabin or deckhouse or fitting additional deck machinery without ensuring that this will not adversely affect the stability of the vessel.
11. Do not remove any permanent ballast from your boat or any substantial weights fitted low down in the boat without seeking advice on the effect it will have on your vessel's stability.

Detecting a Stability Problem

Lack of stability may first be detected by unusually heavy rolling, the slowness of the vessel's roll, a tendency to list either with wind or wave motion, the deck edge regularly submerging in a seaway and a reluctance to come back to an upright position after applying helm.

A recognised surveyor of ships should be consulted whenever substantial alterations to a boat are contemplated or a naval architect if there are any doubts regarding a vessel's stability characteristics.

Major modifications on commercial ships must be re-approved and surveyed by a recognised surveyor with records of the approval work and construction forwarded to Maritime New Zealand.

Contact us for more help

If you have any questions about this safety bulletin, please contact our Wellington office.

Phone:

New Zealand (toll free):
0508 225 522

Calling from outside New Zealand:
+64 4 473 0111

Email:

enquiries@maritimenz.govt.nz
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