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 TB 55-1900-232-10
full scope until sufficient water depth is available.
3-4.2 TOWING SPEED. Important factors in determining a safe towing speed are: material condition of the tow, sea
states, towing direction relative to the surface waves, wind velocity and direction, hull type of the tow, tug horsepower
and available powering assistance from other tugs or the tow's power plant.
The towing speed should be chosen to minimize the probability of damage to the tow. Special care should be exercised
when towing damaged vessels and flat bottomed craft to avoid excessive seakeeping motions and pounding When
necessary, the towing course and speed should be chosen relative to the sea state and the wind direction to keep the
towed vessel motions within safe limits
Barges generally should not be towed faster than about 8 knots under mild sea conditions. Small service craft and some
dry-docks should be limited to about 6 knots. Deterioration of weather conditions requires appropriate speed reduction to
ensure continued safe towline loading. When towing larger surface ships, the speed limitation usually is a function of the
tug's capabilities.
3-4.3 TOWLINE SCOPE. The towline scope employed during a tow depends primarily on four factors'
a. Type of towing rig employed
b Water depth
c Catenary required to absorb changes in towline tension
d Scope required to keep the tug and tow "in step".
To estimate the towline scope required, it is first necessary to estimate the steady towline tension which will be required
to maintain the desired towing speed. Having an estimate of the total tow resistance, it is then possible to compute the
catenary which will be associated with a chosen towline scope and towline rig. Paragraph 5-4 4 presents a simple
formula for estimating the catenary. For hawser scopes greater than or equal to 1,000 feet, Figures 5-4 through 6-12 will
provide catenary depth directly, given hawser tension. Catenary and scope also can be used as indicators of tow hawser
tension and changes in tension. The AAJ technical manuals have tables that permit easy interpretation of scope,
catenary and tension. The scope should then be chosen to provide an adequate catenary for the absorption of changes
in towline tension, without exceeding the water depth. Dragging the towline on the sea floor will damage the hawser
through abrasion and could lead to fouling the towline on a sea floor obstruction in addition to losing control over the tow.
If the surface wave pattern has a predominant wavelength, an attempt should be made to adjust the towline scope so
that the tug and tow ride on crests of the predominant wave components at the same time. Adjusting the towline in this
fashion may keep the tug and tow "in step:' thus minimizing changes in towline tension caused by seakeeping motions
Refer to Paragraph 3-5.2.
3-4.4 TOWING WATCH. With the tow streamed, the towing watch shall be set to observe the tow, towing machine,
towline and the tow's seakeeping performance. The tow watch shall routinely advise the Officer of the Deck of conditions
observed. On board newer tugs, much of the information Is displayed in the pilot house and control stations.
SECTION V
3-5 SHIP HANDLING AND MANEUVERABILITY WITH A TOW
With the tow underway, the tug begins to slowly accelerate to towing speed. Rudder orders are
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