8.1 Introduction

Slamming (water impact) loads are important in the structural design of all high-speed vessels. Further, the occurrence of slamming is an important reason for a shipmaster to reduce the ship s speed. It is also an important effect in calculating operational limits (see section 1.1). The probability of slamming is found by defining a threshold relative impact velocity for slamming to occur (see eq. (8.142)). An often-used criterion is that a typical shipmaster reduces the speed if slams occur more frequently than three out of 100 waves passing the ship. It may be misleading to talk about a threshold velocity. There is no threshold for slamming as a physical process. Further, the conventional way of defining a threshold velocity does not reflect the effect of the structural shape. For instance, for a high-speed vessel with slender lines in the bow, the procedure may say that slamming occurs on the bow part of the hull, although, in reality, it is not a problem. In order to come up with better criteria, it is necessary to study theoretical models for or perform experiments on water impact against wetdecks and hull structures typical for high-speed vessels. This is also necessary in order to develop rational criteria for operational limits due to slamming. The criteria should be related to slamming loads used in the structural design or, ideally, to structural response due to slamming.

Wetdeck slamming (Figure 8.1) is important for multihull vessels. The wetdeck is the lowest part of the cross-structure connecting...