Boat Impact Energy Calculator

REF: EN-312-PHYSICS

Use this tool to calculate the total kinetic impact energy generated by a vessel during berthing or a collision. This calculation is essential for marine engineers and dock owners to correctly size marina fenders, seawalls, and mooring structures. The formula accounts for the vessel's displacement, approach speed, and the hydrodynamic added mass (the volume of water that moves alongside the hull).

INPUT PARAMETERS
> SYS_UNIT:
Typical range: 1.1 to 1.8
> OUTPUT_BERTHING_ENERGY
0.00 FT-LBS

The Physics of Berthing Energy

When a vessel docks, the kinetic energy it carries must be absorbed by the fendering system to prevent structural damage to both the boat and the pier. Because energy scales with the square of the velocity, even small increases in approach speed dramatically increase the force of impact.

Calculation Variables Explained:

  • Vessel Displacement: The actual operating weight of the vessel. Heavy boats possess massive inertia and require much larger energy-absorbing fenders.
  • Approach Speed: Typically calculated between 0.5 to 2.0 knots for standard berthing. Because speed is squared in the kinetic energy formula ($E = \frac{1}{2}mv^2$), doubling your docking speed quadruples the impact energy.
  • Hydrodynamic Added Mass Coefficient (Cm): When a boat moves sideways through the water, it pushes a large volume of water with it. Upon impact, this "entrained water" continues pushing against the hull. This factor usually ranges from 1.1 (for sleek hulls) to 1.8 (for flat barges). 1.2 is a safe default for standard yachts.
Engineering Note: This calculator provides the raw total kinetic energy. In professional dock design, engineers apply additional modifiers like eccentricity (hitting at an angle) and berth configuration to finalize fender sizing.