The computational tool impact2d is specifically developed for dynamics simulation of boats and ships which operate at high forward speed. The tool combines 2D+t theory with a two-dimensional potential flow solver which incorporates a non-linear representation of the free water surface.

2D+t theory is a technique to approximate the three-dimensional flow around a moving body with several two-dimensional flow problems in earth fixed cross section which the body is passing. The technique requires the ship to be a slender body and is able to resolve the diagonal waves of a ship's steady wave system. As such, it is a good approximation for ships operating at Froude numbers above 0.5 because the transverse wave system will not effect the hull at such high speed, leaving the diagonal waves as the most relevant component.

The flow solver consists of a Boundary Element Method to solve the flow as boundary value problem and a Mixed-Eulerian-Langrangian scheme to track the free water surface in time and apply fully non-linear boundary conditions. As such it is able to resolve flow features like jet and spray evolution which are important for ships operating in the planing or semi-planing regime.  

A motion solver is integrated in the tool which allows for dynamic applications such as seakeeping, dynamic stability or even more complex setups like launching of planing boats from a moving mother-ship. A general drawback of the 2D+t technique are three-dimensional flow effects which typically occur at the bow, the chines and the stern of the ship. While finding the right trim and sinkage of a steadily moving planing hull might be challenging without a properly calibrated correction model (Soproni 2015), reasonable predictions can be expected for the motion simulations. Recent developments are focussed on prediction of maneuvering forces on planing hulls and inclusion of effects of level ice.