OK, I have heard enough.
I was hoping that one of our self-described nautical experts would have explained this by now.
When the hull of a boat sits lower in the water as the boat speed increases it is called "squat" or "hydraulicdynamic draft increase"(see
http://translate.google.com/transla...ute/ima/suh.htm&prev=/search%3Fq%3D.The US Corps of Engineers refers to it as "squat" in
http://www.usace.army.mil/publications/eng-regs/er1110-2-1457/entire.pdfGuidelines for channel design and construction.
The most comprehensive discussion I could find on the subject is in "Mathematical and Computational Techniques for Predicting the Squat of Ships
Tim Gourlay Thesis submitted for the degree of Doctor of Philosophy
THE UNIVERSITY OF ADELAIDE Department of Applied Mathematics February 2000
http://216.239.51.100/search?q=cache:cxU1248uzoYC:academic.amc.edu.au/~tgourlay/theweb.psI first learned of this phenomenon many years ago in an article about an accident the Queen Elizabeth 2 had in 1992 near Cuttyhunk, US. The pilot knew how much water the QE2 drew at rest. They took a high speed shortcut across a portion of the bay which should have had minimal clearance. But due to the "squat" at speed, she scraped bottom and caused several million dollars in damage.