FIGURE L-1. Six Independent Ship Motions.
timately, use of synthetic towlines was restricted in the U.S. Navy.
The problems with nylon hawsers have resulted in major studies of mechanical properties of rope construction
and chemical properties of the materials Basically, the strength of such ropes has been found to be affected by
sunlight, chemicals, salt water and-above all-the cyclic load history of the rope. Current research may result in
better ropes and more reliable methods of predicting their strength, thereby permitting re-introduction of
synthetic ropes into towing. This work is a major ongoing effort, and will not be discussed further in this
L-3 EFFECTS OF TUG AND TOW MOTIONS ON TOWLINE DYNAMICS
This section briefly describes the project to quantify towline dynamics. The behavior of a wire stretched in water
between variably-distant endpoints is discussed first, because the hawser effects on the tug and tow must be
known in order to solve the ship motion problem. The ship motion problem is then discussed
L-3.1 WIRE TOWLINE BEHAVIOR . Methods for predicting five degrees of ship motion in response to wave
action have been in use for some time. The sixth degree, and the most important to towing-surge-normally was
not addressed. Surge has been included in the most recent work The special towing problem of examining the
motions of two ships connected by a towline required a significant es