Recommended is Belhammer Marine (https://www.suzuki-kikoh.com/bhMarine/pdf/bhm-cat.pdf).
This is not usable for parts that use friction such as cone clutches and multi-disc wet clutches, but it can be used for internal combustion in general for parts other than friction transmission, and measures against tidal mixing are largely applicable, and it can be expected as an emergency trouble avoidance at sea.
In addition, the recommended amount of addition is about 5% of the amount of oil for the first time in large engines (large capacity), and 2.5% can be added at the time of oil change after the next time to bring out the effect.
Currently, only 1 liter is available for sale, but 20 liters can be produced and sold in about 2 weeks.