Free Surface Effect for Existing Vessels common practice

[green_mango]

Hi, What's the standard practice towards free surface effect when using MaxSurf. Do you just use the maximum, actual filling level or FSM according to IMO A.749(18). Generally speaking I think the maximum should always be used for that extra factor of safety. But I've come across a situation where the vessel barely passes the maximum [maybe about 10% over the required in the weather criteria], so I was wondering if there was a case where IF the vessel fails the maximum but passes the actual filling level and the IMO one should that be taken as a pass or should additional measures be taken to improve stability.

 

[TANSL]

Normally, when tanks are full (which they shouldn't be at more than 96% of their capacity), given the very large volume, there are no problems with the free surface effect. In other situations, such as when the liquid surface inertia is the same but the volume is much smaller, free surfaces can cause problems.

Several loading scenarios with different consumption rates must be studied to determine if any of them present problems due to free surfaces.

These detrimental effects are avoided with long, narrow tanks or tanks equipped with lightweight longitudinal bulkheads.

Fortunately for serious designers, Maxsurf won't provide solutions to these problems. It will only give you the results for the loading condition you specify. Your knowledge of naval architecture will determine how to address the problem.