Background
Propeller tunnels (also called propeller pockets) recesse into the bottom of a planing hullparametric hull form definition because the effective planing bottom geometry differs significantly from the outer hull envelope. The tunnel change the effective deadrise seen by the planing flow.
Setting Up a Tunnel Hull in NavCad
In the , This activates tunnel geometry data entry fields:
- Recess depth: The vertical depth of the tunnel into the hull, measured from the bottom shell slope to the top edge of the tunnel at the transom.
The propeller's immersion depth relative to the tunnel geometry affects the prediction. Enter the tunnel recess depth to allow NavCad to correctly compute the .
Verification
After setup, run the Savitsky prediction and check the trim angle and resistance curves for physical reasonableness. Tunnel hulls often show lower running trim and higher top-end predictions compared to equivalent open-bottom hulls
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