By default the planing template accelerates the boat to full speed in 0.1 seconds, which is clearly not realistic. We do this in order to reach the steady equilibrium in as little compute time as possible, assuming the result at steady equilibrium the goal. But you can change that (knowing that it will take longer to compute):
The displacement template computes the ramp up time using an acceleration of 1 m/s^2, but you can override the ramp up time there as well.
Remember that if you’re running the CFD at full-scale but trying to compare it to the model tests, time in the model test scales by the square root of the scale factor. If you really want to compare the CFD and model tests, it’s best to run the CFD at model scale (and remember to change the water to fresh water in Orca3D Properties). Then compare the resistance in the CFD to the raw data from the model tests. That way you remove any questions about how the model data was expanded to full-scale. But one of the advantages of CFD is that you can run the simulations at full-scale and avoid expanding the data to full-scale altogether.
In general, the transient phase as the boat is getting up to speed is not very realistic, since the acceleration is constant. A more realistic approach is to do a self-propelled run, with a ramp up on the propeller RPM. Then the propellers are accelerating the boat, just as in the real world. Of course this takes longer to compute.