Ch. 5 Flashcards
Describe the important aspects of the hull of a tug used for shipwork.
A tug for shipwork will have a heavily constructed hull with low freeboard. It should be stiff enough so that a strain on a line leading to the side will not capsize it. The bulwarks are tumbled home so that they will not be damaged when the tug goes alongside a ship even if they are both rolling a bit.
Is the hull reinforced?
Yes, the bow of a conventional or ASD is heavily reinforced since this is the area that comes in contact with the ship when the tug is pushing full ahead against the vessel. The bow should have large fendering to distribute force over a large area.
Why are deck structures set so far inboard on harbor tugs?
The wheelhouse is set inboard to prevent it from coming into contact with the ships side at the ships flare or overhang.
What is a bullnose?
A bullnose is a large closed chock near the bow of a tug to provide a fairlead for the tugs headline and springline. It should be large enough for the large working lines and the splices to pass through freely.
What is a staple?
The staple functions as the tugs towing point and is subject to extraordinary strain. The staple is the primary focal point of the tugs bollard pull when on the towline. The staple itself must be heavily constructed and mounted in such a manner that connects it to the tugs internal frames.
Where are the bitts located on a conventional american tug?
H bitt installed fore and aft in the fore deck, Another H bitt installed athwartships aft of the deck house and quarter bitts installed to augment the forward and aft H bitts.
What are the structural for the bitts and deck fittings?
Must be large enough on which to belay the large working lines, and strong enough to withstand the heavy strains imposed upon them. The bullnose forward cruciform bitt and the quater bitts must be set inboard enough so they will not come in contact with the ships hull and cause damage.
What type of mast should be installed on a harbor tug?
A “dipping mast” should be installed so that it can be lowered when working under overhanging obstructions on the ship.
What structural characteristics of a ship can make it difficult or dangerous for a tug assisting it?
Poorly located chocks and bitts installed too far forward or aft or beneath overhanging obstructions could damage or endanger the tug. External hull fitting on the ships side, sponsans, pipes, and rubrails can also be a hazard.
What are pocket or recessed chocks and why are they useful?
“Pocket chocks” are set into convenient locations in the ships side in such a way that they have a bar or pin for the tugs lines to be secured to.
What are three functions of tugs fendering?
Absorb and dissipate energy, enhance or reduce traction, create spacing between tug and ship.
