8.
HYDRODYNAMISKA EFFEKTER
8.1
Marine Accident Reporting Scheme (MARS) Report No. 200026
Squat Confusion As a pilot operating in shallow waters an important part of my discussion with a ship's Master is about squat and how it affects his ship. Squat tables are becoming more common but there are still many vessels that do not carry this information. It may interest the reader to hear some of the comments I have received when I have asked about squat...... On a 120m LOA fast feeder container ship: "We do not have any squat Mr. Pilot." When I expressed some surprise at this and suggested that I would expect about 1.5m, maybe more, on a vessel of this type, I was met with an emphatic "No Mr. Pilot, if we had that much squat the deck would be under the water !" On a 110m LOA fast feeder container ship: "Yes we have squat tables but I don't think they are right. I have been reading the midships draught and it does not change no matter what speed we do." On a 160m LOA 9m draught bulker: "We have no tables but we have a squat gauge." I said that I had not heard of such a device and asked the Captain how it worked. That was not known and on further questioning it appeared that this gauge was actually showing trim....."Yes Mr. Pilot - Squat !" It would appear that this subject still causes confusion. Squat: The decrease in clearance beneath a ship which occurs when the ship moves through the water and is caused both by bodily sinkage and by change of trim. The effect is accentuated in shallow water and is reduced with a reduction in ship’s speed.
Fig 30
Risk for bottom contact
8.2 NAVIGATION AND VESSEL INSPECTION CIRCULAR NO. 2-97,CH-1 (USCG) Guidance. The maneuvering poster and other maneuvering information required in IMO Resolution A.601(15) is more detailed than the information required by 33 CFR 164 or 46 CFR 35. Squat characteristics and additional engine information must be displayed along with the general turning circle information. The pilot card, required to be filled out by the vessel master, provides the pilot with quick reference to important propulsion, loading, and maneuvering information. H. Minimum Under-Keel Clearance. (1) Background. Beginning January 21, 1998, tank ship owners or operators must provide tank ship masters with written under-keel clearance guidance. Prior to transiting port, the tank ship master shall plan the ship’s passage using the owner or operator’s written guidance and estimate the anticipated underkeel clearance. The tankship master and the pilot shall discuss the transit plan including the anticipated under-keel clearance. Tank ships or tank barges that are 5,000 GT or more and are fitted with double bottoms covering the entire cargo tank length are not required to comply with this regulation but are encouraged to do so.
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