Background
Shallow water affects both hull resistance and propeller performance. The resistance effect arises from the restriction of flow under the hull in shallow water or confined channels NavCad model this through the Environment entry. The propulsor effect changes in wake fraction and thrust deduction as water depth decreases was added in NavCad 2025.
Shallow Water Resistance Environment Data
To enable shallow water resistance prediction:
- Open the Environment Data entry: Edit | Environment from the menu.
- In the Shallow/channel group, enter the Water depth and select the Type (Shallow water or Restricted channel).
- For a restricted channel, also enter Channel width and Channel side slope.
- Enter Hull girth the maximum girth of the submerged hull body. An estimate is available from beam, draft, and section area.
- Run the resistance prediction. The shallow water added resistance appears as a separate component in the results.
Shallow Water Hull-Propulsor Correction
The NavCad hull-propulsor coefficient correction for shallow water adjusts the wake fraction and thrust deduction values used in the propulsion analysis to account for the altered flow field around the stern in shallow water. The correction activates automatically when shallow water is defined in the Environment ata.
The practical effect is that shallow water conditions will show modified propulsive efficiency predictions compared to deep water typically reduced wake fraction and altered thrust deduction as water depth decreases.
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