Tuesday, June 7, 2011

Top 10 Towing Vessel Material Failures—Part III

Excerpted from “Top Ten Deficiencies Found on Vessels.” Full text available on http://homeport.uscg.mil/. Navigate to missions/investigations/safety reports.

See Part I here and Part II here.

Most of the failures that cause a towing vessel’s diesel generator to stall or trip off the line are related to the diesel end of the generator set. The most common failure items are voltage regulators and wires.

Control Air Valve
Mechanical linkage has been known to come loose, most commonly between the pilothouse control and the air supply.

Propeller and Shaft
Eliminating the occasions where a propeller was fouled by a floating object or a line, there are numerous instances of actual propeller loss. When a blade was lost, we see that overspeed and/or shutdown often follows, but not always.

When the entire propeller is lost, shutdown of its drive engine always follows promptly. Assuming a twin-screw vessel, the immediate consequence is reduced maneuverability until the speed drops to a point where single-engine maneuverability can be achieved.

A broken propeller shaft (especially a break in the tail-shaft section) has the same effect as a lost propeller, but with the added possibility of the shaft sliding aft, such that the propeller jams the rudder.

Hull Plating
Sometimes when cracked or defective hull plating is found, the origin of the defect cannot be determined. Given the age of some of the vessels, it can be assumed that the defect occurred naturally, without a collision, allision, or grounding.

Owner/operator recommendation: Inspect the underwater hull and bottom plating when the rudders, propellers, and shafts are inspected.