How much additional height is added to Safety Height based on mast head height?

The additional height added to Safety Height based on mast head height is correctly identified as 25 feet. This standard is established in marine navigation practices to account for the height of a vessel's mast when determining safe clearance for obstructions such as bridges and power lines. The rationale behind this specific figure is to ensure that a vessel can pass safely under such structures without risk of collision or damage, considering various factors including the vessel's loading condition and the influence of wave action.

Using 25 feet as an additional height helps to create a buffer that accommodates not only the fixed height of the mast but also potential variances that might arise due to environmental factors. This guideline assists navigators in making informed decisions when plotting routes, particularly in areas with known vertical constraints. In contrast, the other options do not align with regulatory standards or commonly accepted practices in maritime navigation for determining ample safety clearance from overhead obstructions.