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Commercial towing vessels depend on tow lines, also known as hawsers. They also depend on Mark Tool to keep those lines protected from chafing and from the harmful effects of seawater.
Whether used for offshore oil and gas operations, dead-ship towing or salvage, the towing hawser is the key element in the tug-tow connection. Hawsers used for conventional tugs are essentially a thick cable of wire rope. The condition of these lines is critical; they must be inspected on a regular basis, lubricated regularly and shielded against excessive wear.
Towboat pulling a production platform
The U.S. Navy Towing Manual has detailed information about inspecting wire rope and determining when you should replace tow hawsers due to wear or damage. It singles out steel as the preferred hawser material due to its strength (with target sleds being one exception where synthetic fiber lines are sometimes preferable).
Steel wire rope is also a safer choice because it doesn’t stretch as much as natural and synthetic fiber lines. That means it presents less danger to workers when it fails under high loads, which causes loose ends to “snap back.”
However, not all steel is created equal. To be sure your hawsers can withstand harsh marine conditions (including the corrosive effects of salty seawater and aquatic biofouling), it’s critical that the proper construction methods and materials go into construction.
Traceability (the ability to trace a rope’s construction history) is an important part of this. That’s why American-made wire rope can be identified by special core marker materials built into the heart of the tow line.New towing equipment (including wires, pennants, stretchers, ropes, towing plates, shackles, rings and bridles) should come with approved test certificates.
Traceability and proper construction are critical. So are maintenance and care. For example, washing the towline with fresh water and lubricating after each tow can help slow down corrosion. The core of an unprotected tow line will remain saturated with salt water, however. That’s why Mark Tool provides marine-grade polyurethane UreGuard tow line protectors made of durable polyurethane. These sheaths are 95A durometer and will outlast any conventional marine chafing gear or marine chafing boards.
UreGuard protectors are made with tapered ends and end washers that serve as bearings, holding the rope while also allowing free rotation.
UreGuard towline protectors are made of two halves bolted together with high-grade, non-corrosive bolts for easy installation. The tapered ends of the Mark Tool towline protectors act as bearings to prevent premature line parting and lost tows.
A tug master should always know the condition of his tug, towing hooks and fittings. Steel towlines and ropes should have a safe working load at least two to three times the bollard pull of the tug. Ancillary equipment, including wire towage protectors and thimbles, should be regularly inspected.
Unprotected “Bird Caged” wire tow line.
Popped core wire tow line.
Regular tow line inspection means looking for signs of ultraviolet or chemical degradation, worn or fused strands, overstretched sections and kinking (including popped cores and “bird caging,” illustrated above). It also means having the sleeves and protectors you need for your main and secondary tow lines. Mark Tool tow line protectors are available in lengths of 5-10 feet or can be manufactured to your specifications. We’ll be happy to custom-build them to fit any size cable or rope.