* In the application of the formula, a decision should be made as to whether the trim and squat values should be added. In the standard case only, the squat value is used to determine the “actual channel depth.”
Project (Advertised) Waterway Depth = Waterway Depth - Overdepth Allowance
In addition to the factors affecting Waterway Depth included in this section, others that should also be taken into account include:
The draught of the target vessel that will be using the waterway is based on the anticipated ship traffic for the proposed waterway. These dimensions are selected by an economic evaluation of the ship traffic for the waterway.
Squat refers to the increase of a ship’s draught as a result of its motion through water. It is a hydraulic phenomenon whereby the water displaced creates an increase in current velocity past the moving hull causing a reduction in pressure resulting in a localised reduction of the water level and, consequently, in a settling of the vessel deeper in the water. For various reasons—having to do with hull design, trim and other physical and operational factors—squat may be different at the fore and aft.
Recently, a new equation was developed on the basis of extensive research by Waterways Development to specifically target commercial waterways with vessel traffic and conditions representative of most major Canadian waterways. This equation takes into account the vessel beam in relation to the channel width, contrary to earlier equations that supposed infinite width. This new parameter is of importance since most Canadian waterways have limited width. The equation, known as Eryuzlu Equation # 3 (Ref.: 4, this reference is attached to this manual as Appendix 4), is therefore recommended as the one providing the most reliable results in waterways of limited dimensions. The equation is written as follows:
Z = squat;
d = vessel draught;
D = channel depth;
vs = vessel speed;
g = gravity acceleration;
W = channel width;
B = vessel beam; and
Fw = channel width factor.
With Fw = 1, where W > 9.61 B;
a, b, c are common coefficients: a = 0.298, b = 2.289,
c = -2.972
Fw = 3.1/√W/B , where W < 9.61 B; and