Collisions frequently occur at sea, leading to serious human injury, and damage to property and the environment. Furthermore, the increasing number of offshore platforms means that collisions between vessels and offshore structures are a frequent type of accident. Platforms are at a greater risk of collisions than ships, because they have no avoidance capability when operating. Recently, the expansion of offshore wind farms in response to new green energy requirements has led to wind-turbine installation vessels (WTIVs) being in common use. WTIVs are similar to fixed jack-up rigs, and they are self-propelled because they must be able to quickly relocate during wind-farm operation. Therefore, it is important to consider the operational characteristics of WTIVs when calculating their collision risks. This study develops a new method for analysing WTIV collision frequency and then compares the proposed method with the existing methods. It also discusses the implications of the methods for ship-WTIV collision-frequency analysis.