The demand to sail at high forward speeds in both calm water and in a seaway remains high. For various patrol, search and rescue or military operations attaining high forward speeds is essential. In head and bow quartering seas, the main factor for voluntary speed reduction is the occurrence of large vertical peak accelerations. The occurrence of large vertical peak accelerations imposes limits to the operability of planing monohulls sailing in head seas. A challenge for designers of fast monohulls is to explore different possibilities to increase the operability of planing monohulls sailing in head seas. To achieve this a reduction of the vertical accelerations is required. The operability can be considered improved if the level of accelerations can be reduced compared to a trip at an equal but constant forward speed. This implies that it is possible to sail at a higher speed without increasing the discomfort on board. A solution for increasing the operability of planing monohulls sailing in head seas has been found in proactive control. Vertical peak accelerations have a very short duration. Unacceptably large vertical peak accelerations have a low frequency of occurrence. These two aspects are the incentive for a proactive control system. What makes proactive control unique is the fact that the control is based on predicted vertical peak accelerations. The response of the ship for the next few seconds needs to be simulated real-time while sailing. These predictions should be carried much faster than real-time, since there is little to effectuate control because of the high relative velocity between ship and incoming waves. In this dissertation proactive control of the forward speed, also termed automated proactive thrust control, has been presented. The purpose of this study is to show the level of reduction of the vertical accelerations possible with automated proactive thrust control.