The old ship's lifeboat system that was served it well for its job in an emergency. However, it was never to be used day in day out. This system was never designed to be used that way.
the system was crude and not up to standard in a modern boat.
The pipe runs are especially crude and the feed pipe comes off the bottom of the tank and know filter at the tank end as a first line of defence against dirt getting to the engine filter system.
The end result of the lack of proper filter system is this contamination in the filter on the engine.
The diesel in the container is black as is the filter body, so the first job next week is to drain the fuel tank and get it clear, then renew the pipe work and put an extra filter in line so that the engine as a better chance of not coming to the same result again.
The engine and fuel tank maintenance as not been done by the owner so he is learning the hard way that this has to be done at regular intervals to maintain his engine and keep it going.