Question 13 AT01 - Assistance Towing Endorsement

The Correct Answer is D **Explanation for Correctness (D): The catenary comes clear of the water** When towing at a proper speed, the tow line is weighted (usually with chain or the weight of the line itself) so that it forms a substantial downward curve, or catenary, which rests partially or fully in the water. This submerged catenary provides crucial elasticity and acts as a natural shock absorber, damping out sudden jerks caused by waves or vessel movements. If the towing speed becomes too fast, the hydrodynamic drag on the lead vessel pulls the towed vessel forward with such force that the tension in the line significantly increases. This increased tension pulls the slack out of the line, lifting the catenary completely clear of the water. When the catenary is straight and clear of the water, the shock-absorbing capacity is lost. Any sudden movement will result in a sharp, potentially damaging, shock load being transferred directly between the vessels, which is a clear indicator that the speed is excessive. **Explanation of Incorrect Options:** **A) The tow line feels like it is "jumping" when touched:** While rapid, irregular motions ("jumping") of the tow line are certainly signs of excessive strain or improper synchronization (snatching), they generally indicate that the tow line is already too taut and experiencing shock loads. However, the root cause—the catenary lifting clear—is the primary observable indicator of *excessive speed* leading to this high tension. The complete absence of a submerged catenary (Option D) is the more definitive operational indicator of critically high speed/tension. **B) The vessels are not in step:** "Not being in step" means the lead vessel and the towed vessel are rising and falling due to wave action out of sync. This often results in snatching and shock loads, but it is primarily a function of the tow line length relative to the wavelength and the relative sizes of the vessels, rather than a direct indicator of excessive average towing speed. While higher speeds can exacerbate snatching, the synchronization issue is fundamentally related to length and wave period. **C) The towed vessel goes "in irons":** "In irons" is a term (often used in sailing) describing a vessel that is stopped head-to-wind and cannot maneuver. In towing contexts, this phrase is sometimes loosely used to mean the towed vessel is uncontrollable or not steering properly. This condition is usually related to poor rudder angle, improper trim, or issues with the bridle attachment, and is not a direct indicator that the *speed* of the tow is too fast.