Feature 1 | CRUISESHIP TECHNOLOGY
Figure 2. (includes Tables 3 and 4) Maximum squats in open water conditions.
there also are a few user-friendly short-cut formulae. Figure 1 indicates that she would go
aground at the stern in open water at a forward speed of 17.08knots. Te equation that I used is:
Table 2 Table 3 Maximum Squat = (CB x V2 ) / 100metres
in open water conditions. My short-cut formula over-predicts a few
cms on the high and therefore safe side. Figure 1 indicates that Queen Victoria
would go aground at the stern in a confined channel at a forward speed of 12.08knots. Tis lower speed when grounding shows the influence of adjacent riverbanks producing greater squats.
Maximum Squat = (CB x V2 ) / 50metres
in Confined Channel conditions. Again, this is a short-cut formula that I
have developed. It errs a few cms on the high and therefore safe side. Figure 1 portrays how the squats at each
sometimes refer it to being in restricted waters ie. restricted in water depth only. When a vessel is operating in water
with breadth restraints such as riverbanks or canal sides, she is said to be in confined channel conditions. As a ship proceeds along a river or canal the forces will be reflected from these banks back onto the vessel. Squat in confined channels can be over twice that measured in open water. Te width of influence is where the ship
changes from being in a confined channel to being in open water conditions. It can be given as a multiple of the vessel’s breadth moulded, perhaps later transposed to a distance in metres. Width of influence
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changes with ship type and block co-efficient. See later notes.
Victoria’s squat curves . Figure 1 shows parabolic squat curves for when the Queen Victoria is in open water and in confined channel conditions. See maximum squat values in Table 3. Te (Cb) used is 0.600. It was assumed that when static, there
was a 1.75m under-keel clearance even keel, extending from her Bow to her Stern. Tere are many complicated detailed
formulae suggested by researchers for predicting maximum ship squat. However,
forward speed in a confined channel produce twice the squats for when Queen Victoria is in open water. Because the Cb < 0.700, all these maximum
squats are at the stern, Figure 2 illustrates what happens if the H/T
was changed to 1.20, to 1.30 and to 1.40 in open water conditions. See maximum squats in Table 3 and Table 4. Te higher the value the H/T, the less will be the corresponding squats. Maximum squats will vary directly with the inverse of H/T. Again, the Cb is 0.600. Figure 3 portrays the maximum squats
between the conditions of open water and confined channels for the Queen Victoria. Tis time H/T is 1.20, for example say (water
The Naval Architect February 2009
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