Date (Y-M-D): 2000-11-20
Subject: The use of roll damping paravane systems (paravane stabilizers)
Casualty investigations into the capsize and sinking of a few Canadian fishing vessels have indicated that the loss of one of the roll damping paravanes may have contributed to their capsize. The purpose of this Ship Safety Bulletin is to caution the operators of vessels which are equipped with this type of roll damping system (see Figure 1) against the hazards associated with their use such as, reduction in vessel's stability, system failure from poor maintenance and operational hazards.
Paravane roll damping systems, commonly known as paravane stabilizers are roll damping devices only and are used for reducing rolling motion of the ship thereby improving the comfort of the ride and reducing crew fatigue. They DO NOT improve stability of the vessel.
Due to the additional weight of mast and boom structure and the rigging associated with the installation of a paravane roll damping system, the center of gravity of the vessel will be higher than for a similar vessel without the system. This causes a reduction, sometimes significant, in the stability of the vessel, what may be further aggravated by ice build-up on these surfaces in cold weather. Owners of vessels demonstrating marginal stability should seek professional advice before retrofitting the paravane system on their vessels.
As the failure of various elements of the paravane system may lead to the collapse of the system and endanger the crew or the vessel itself, it is of vital importance that all elements of the system are maintained in good working condition. Particular attention should be drawn to the anchoring points of the rigging including fore stay, after guy, paravane tow wire, and boom heel and safety wire attachment points.
All essential elements of the system should be regularly inspected for mechanical or corrosion damage or wear e.g. stays and safety wire for kinks or broken wires in strands, booms for signs of bending, boom heel hinges for cracks or excessive wear, etc. Damaged or worn parts should be readily replaced.
Handling of Paravanes
Care should be exercised while handling paravanes during retrieval operations. These operations can be quite dangerous, exposing the vessel to the risk of physical damage and crew members to the risk of serious injury, particularly for those arrangements where the paravanes are towed from a fixed point at the boom head.
Rough sea conditions can significantly increase the dangers associated with the handling of paravanes. Safe practice would therefore suggest to retrieve and secure the paravanes before the sea conditions become too rough for safe paravane handling. Careful attention to weather warnings and prompt action will ensure that the crew and the vessel will not be exposed to these risks.
Paravane (fish) fouling
Paravanes are subject to the risk of fouling/snagging on fixed fishing gear, debris, or other underwater obstructions. This may result in excessive forces being exerted on the boom and rigging. Due diligence will help to prevent the fouling of paravanes along with the use of updated nautical charts to identify underwater dangers that should be avoided to prevent paravane's fouling.
Incidents where the paravane breaks the surface, or broaches, may occur when the depth of tow is not sufficient or when the paravane is damaged or warped. While the paravane is out of the water, it is free to swing in the air and may strike the vessel or someone onboard.
Risk of paravane broaching can be reduced by ensuring that there is a sufficient length of tow line so that the paravane will remain submerged and by not operating with warped or damaged paravanes.
Incidents where the boom head dips into the water may occur when the set-angle of the boom (from horizontal) is too small for existing wave conditions. When this happens, excessive forces are exerted on the boom structure and rigging and may result in damage to the system and the vessel.
Ensuring that the boom is set high enough so that its head will not dip in the water while the vessel is under way would reduce this hazard.
Where the boom assembly is unrestrained from vertical movement, it may swing violently in rough seas before the paravanes are deployed or when they broach. This situation presents a danger to both the vessel and personnel onboard.
Restricting the vertical movement of the booms may reduce the risk associated with the boom swinging. This could be accomplished by incorporating some form of a "lock-down" mechanism, such as the hydraulic rams seen in some installations, boom tie-downs or incorporating "crutches" for the stowage of boom poles.
Figure 1 - Illustration of Paravane Roll Damping System
Keywords: Questions concerning this bulletin should be addressed to:
2. Fishing Vessel
3. Roll Stabilization
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