Towing is an old and well-developed procedure. Rescue and salvage towing generates a necessary sense of urgency. Conditions of a tow, weather, war zones, and other factors commonly make towing a time-critical operation. While certain ships and watercraft are designed to offer towing services, all ships can take a tow in an emergency.
Towing is a routine operation for tugs. Good practice of seamanship is necessary to accomplish the mission without endangering the tow, tug, personnel, or operational schedules. While nearly all transocean and coastal tows are completed uneventfully, emergency conditions must be expected. Proper preparations must be made for emergency conditions. Good planning, preparation for emergency situations, and correct shiphandling are necessary elements of towing.
Present day towing has evolved from the learning and often relearning of several obvious lessons that are commonly overlooked or forgotten in the zeal to accomplish the mission. The following lessons remain valid throughout the history of engine-powered towing. They also distinguish between simple barge towing and open water coastal and/or ocean towing. When planning and tasking a towing operation--
- Do not keep tugs waiting unnecessarily while
preparing or disposing of tows after the mission has been accomplished.
Also, when the draft of the towing tugs is too great for the depth
of water at either terminal, prearrange the delivery or take-over
of the tow before the deep sea tug arrives outside.
- Do not use large tugs to do work that available
smaller and less powerful or less seaworthy tugs can do. Estimate
the required towline pull and horsepower of the towing vessel
before assigning a tug.
- Do not use tugs or other unsuitable craft to
do work beyond their capacity (also consider the towline pull).
- Do not use tugs on tasks for which they have
insufficient endurance unless provisioning or refueling them en
route has been arranged.
- Do not unnecessarily use tugs designed or especially
suited for duty in combat zones in rear areas. The large tugs
are well suited for duty in combat zones. The large salvage tugs
are suited for combat towing and for emergency salvage or firefighting
in combat areas.
- Do not use tugs in forward areas that have insufficient
stability, reserve buoyancy, armor to ward off attacks by enemy
planes, or subdivision to enable them to survive even moderate
- Do not use tugs unnecessarily for standby duty
on salvage or rescue operations. Tugs should not be ordered to
stand by unless there is a definite possibility that their services
may be needed and they can render the service likely to be required.
- Do not remove tugs unnecessarily from areas where
tugs equipped for rescue (salvage or firefighting) may be required.
- Do not use tugs unnecessarily for tows that other craft scheduled to make the same passage could do or that a ship may be more easily made available for than a tug.
There are three general types of towing missions:
- Administrative towing missions are routine in
nature. They reposition floating equipment within the confines
of the terminal harbor areas; dock, undock, and assist large ships
in port arrivals/departures; and perform short-range missions
in protected waters where only light towing gear and equipment
is required. Administrative towing usually requires towing
gear and equipment normally found aboard as part of the tug's
basic issue items. These items are wire rope bridles and pendants,
shackles, wire rope clips, and swivels. This equipment is well
suited for short duration towing in waters protected from the
effects of coastal and ocean seas.
- Special towing missions generally transit unprotected
coastal waters and the open ocean. These missions require considerably
larger and stronger tugs using heavier and stronger towing gear
to withstand the violent stresses encountered in open coastal
and ocean seas. Normally, these tugs have greater towing power
(larger engines and overall heavier equipment and construction)
and are equipped with towing machinery, such as single- and double-drum
wire rope towing winches; tow wire guides, rollers, and pinions;
cranes or winch/boom assemblies to handle the tow rigging; and
a small workboat for boarding and inspecting the tow while en
route. Towing gear for these missions include heavy chain bridles
and pendants (anchor chain), plate shackles, retrieving wires,
emergency towing bridles, towlines (hawsers), flooding alarms,
pumps, and anchors. Large floating equipment, such as floating
cranes (BD) and floating machine shops (FMS), are equipped with
their own towing gear. Such heavy gear cannot be carried as basic
issue items aboard tugs because of weight and cube.
- Rescue/salvage towing missions have two forms: planned and opportunistic. Planned rescue and salvage towing requires generally the same conditions of a special towing mission. An additional hazard is trying to tow equipment that is not seaworthy because of battle damage, grounding or other non-operational status. Opportunistic rescue and salvage towing occurs when any ship or tug is in the immediate area of a vessel requiring towing assistance to remove it from immediate danger. This type of towing uses any means at hand to remove the stricken vessel from danger. The nature of the operation makes it extremely hazardous to the towing vessel as well as the towed vessel.
The command requesting tow of craft must provide the craft in seaworthy condition with flooding alarms, navigation lights, electrical power for alarms and lights, salvage gear (anchors and pumps), and towing gear (bridle, pendant, and retrieving wires). For suspect or deficient seaworthiness conditions, both the tow and towing command must agree on the risk of tow.
The command accepting the tow must provide tug and towing gear to connect to the towed craft's towing gear. The tug and gear must be seaworthy for the particular mission route and have the appropriate size, horsepower, and control to safely and successfully accomplish the towing mission. On accepting the tow, the towing command accepts full responsibility. Before accepting, seaworthiness must be verified. The tow should be refused if it is considered not fit for sea. Towing is accepted only after the tug's officers complete a comprehensive evaluation and survey of the tow.
Towing seaworthiness means suitable condition for the mission. This concerns all the various technical implications of the tow and towing vessel, including--
- Vessel design and specifications.
- Structural condition and stability.
- Age, maintenance history, and status.
- Reinforcement requirements.
- Hull and superstructure closures.
- Adequacy of towing gear.
- Dewatering facilities.
- Chafing gear.
- Firefighting and damage control facilities.
- Repair parts.
- Tow-boarding facilities.
- Emergency towing gear.
- Waters to be transited.
- Hazards of the route.
A certificate of seaworthiness for ocean tows must be completed. The certificate indicates the general characteristics of the tow, type of cargo, towing gear, lights, and emergency gear aboard the tow.
Hulls not considered seaworthy for open ocean should be transported as deck cargo on heavy-lift, SEABEE, or float-on/float-off ships. Only under extreme emergency situations should open ocean towing be attempted when the tow is not considered seaworthy.
All ships can tow in an emergency; however, only properly designed and outfitted tugs make good towing ships. Characteristically, a tug's superstructure is set forward, allowing the towing point to be close to the ship's pivot point. The towing point is located far from the rudder and screws so that it allows the towline to sweep the stern rail. High horsepower, slow speed, large rudder, towing machine, power capstans, towing points, and a clear fantail characterize a good tug.
All ships can tow and be towed in an emergency. Ships not equipped for towing can use the anchor chain, wire straps, nylon lines, or any combination necessary. A good catenary ensures spring in the towline. Slow speed transfers the lowest dynamic load from the towing ship to the tow. Large ships can easily overpower the tow and excessively strain the towline. The towing ship should keep engine revolutions low for the highest torque and lowest strain and surging.
Administrative point-to-point towing is routine and ensures that both the tug and tow are seaworthy and prepared for the transit.
Rescue towing requires prompt action, often under pressing circumstances of a war zone, salvage operation, or inclement weather.
If a continuous watch is required on the tow, a riding crew is placed aboard the tow. The riding crew provides security, fire watch, damage control, line handling, communication, flooding watch, and defense. It provides the nucleus for fire fighting, damage control, and defensive actions.
Under normal conditions, and after proper securing for sea, most tows can be done without a riding crew. However, there are exceptions. It is far better to secure the tow properly than to provide a riding crew as a substitute security.
Barges, floating cranes, dredges, pontoons, pile drivers, dry docks, and ships can be towed without riding crews. Any hull considered seaworthy can be towed unmanned. A seaworthy hull has watertight integrity, structural soundness, proper position of the centers of gravity and buoyancy, and good stability characteristics. All cargo and equipment is secured.
Long-distance and valuable tows without a riding crew should be periodically boarded and inspected. Since the operation is often difficult and hampered by weather and sea condition, the inspection should be well planned and executed promptly and efficiently.
Using an inflatable boat to transport the inspecting party to and from the tow is recommended. This boat should be equipped with an outboard engine whether or not it is veered aft on a line. This greatly enhances its maneuverability and permits its recovery if the veering line parts.
When preparing a crane, dredge, pile driver, or other floating equipment designed for operation in sheltered waters, it may be necessary to remove high weights; to secure booms, ladders, deck structures, ballast, and trim; and to perform other unique functions due to the hull's design.
Senior marine deck and engineering officers (MOS 880A2/881A2) should thoroughly analyze the configuration and modifications to the hull and recommend it for open ocean towing. Nothing is derived from taking a marginal tow to sea only to lose it.
Inspection must be complete and comprehensive. Tows should be properly trimmed, not over-loaded, and secured for sea. Deficiencies must be identified and corrected before acceptance.
All secured gear is inspected to ensure it is properly tied down. Turnbuckles with wire rope tie-downs are used with good holding results. Manila line lashings effectively hold light gear. After all gear is secured, tie-downs and lashings are inspected to ensure all are taut and holding. Retightening of turnbuckles and lashings may be necessary during long-range tows or prolonged periods of time. This requires the tug's crew to board the tow at sea, an inherently dangerous task.
When large units of high weight must be secured for sea, it is advantageous to weld them to the deck. Welding requires extra time and effort, but the additional safety and security justifies it.
Tows are generally not dry-docked for inspection before being accepted. Suitable hull inspection consists of divers and internal observation and measurements. If a number of checks along the sides, between light and full load waterlines, show adequate thickness of the original hull side plating, the bottom of the craft to be towed is assumed to be sound. A thorough internal inspection should be made. Note the bottom framing, plating, and welds in the forward one-fifth of the craft's overall length. If no evidence of serious deterioration or displacement of hull plating exists, the craft is considered structurally sound.
If the inspection uncovers serious rusting or displacement of the frames, plating, bottom, or weld seams (particularly in the forward one-fifth of the craft's length), the craft should be dry-docked and necessary repairs made. While in dry dock, magnetic particle checks (or their equivalent) of bottom, side, butts, joints, decks, and inner bottom should be made. All defective welds and plating should be repaired or replaced. Structural reinforcing and load distribution may be accomplished with wood timbers.
Craft should be examined thoroughly before towing to avoid special dry-docking of craft. Thickness and magnetic particle checks made during cyclic maintenance and resulting repairs should provide suitable supporting data to avoid special dry-docking.
All flooding alarm systems should be inspected for proper installation and operations. Navigational lights should be tested. Batteries, including hydrometer reading, should be inspected and tested. There must be sufficient battery capacity to support the systems for the duration of the mission. All flooding alarms and navigation lights should have automatic lamp changers.
Packing glands in the stern tube should be checked. The shafts should be properly locked. If a riding crew is aboard, shafts may be allowed to freewheel. The craft's rudder must be locked mid-ships to prevent erratic behavior of the tow.
Commanding officers of the towing ship and the towed craft should agree to the conditions of risk in towing the craft. Risk conditions are based on the seaworthiness and structural condition of the tow, expected sea and weather conditions for the route, and the specifications of the towing ship.
In acceptable risk, the hull, equipment, towing gear, and towing ship are seaworthy and structurally sound.
In calculated risk, tow deficiencies are accepted. The probability of tow safely reaching destination varies with deficiencies.
The commanding officer of the towing ship administers the tow, even when the tow has a riding crew with an officer in charge. In assuming this responsibility, the commanding officer of the towing ship inspects administrative conditions on the tow, with particular attention to-
- Personnel accounting.
- Sanitation facilities.
- Safety, security, and lifesaving equipment on
- General stores, provisions, equipment, and gear.
- Defensive capability.
If the tow is not satisfactorily prepared, the commanding officer of the towing ship will so inform the tow's command to correct deficiencies.
Whenever possible, towing operations should be planned to take advantage of the best weather conditions. Appropriate weather activities should be requested to provide 24-hour forecasts every 12 hours along the intended route, commencing 24 to 36 hours before departure and continuing until arrival. Requests for special weather forecasts should include the intended route and estimated speed.
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