FIGURE 2-19. Nested Rig in Protected Waters.
a. Side-by side. Figure 2-20 shows side-by-side tugs towing a single tow. Each towline should have its own connector
and chafing fairlead. There is no universally preferred method of two tug towline arrangement. Most operators
prefer to tow "side-by-side," with equal hawser scopes; this avoids the risk of sweeping over the other's towline. A
few operators prefer different scopes to minimize the risk of tug collision. In such cases, the more powerful tug is
designated lead tug, with a longer hawser scope. The lead tug may use a longer lead chain to increase the catenary
depth. This reduces the chance of interference, should the following tug suffer some untoward event that results in
its crossing the lead tug's towline
Stern Steering Tug. At times when a tug has a tow at short scope in restricted waters, steering assistance is needed.
This assistance can be provided by another tug, astern of the tow. Usually, the steering tug's main effect is to
restrain the movement of the tow, primarily in yaw. Use of U.S. Navy towing ships for this function is rare and
normally restricted to harbor tugs. Use of steering tugs varies widely, depending upon local practice, tug design and
pilot preference. No attempt is made herein to provide information on steering tug connections.
2-5.4 MANAGEMENT OF TOW LOADS.
Management of tow loads involves design of the towing system before commencing the tow, adjustment of the hawser
scope during the tow and modification of course and speed to reduce dynamic effects of wind and sea conditions. Each
of these functions is discussed in detail in Chapter 5.