Marine propulsion systems are incredibly complex units that have to function efficiently and smoothly without fail. Unlike car engines that can take some wear and tear, along with occasional breakdowns, marine engines must keep performing without any issue.
It cannot afford to a breakdown in the middle of a voyage, since the nearest source of aid might be thousands of kilometres (technically, nautical miles) away. Thus, to keep the propulsion systems functioning effectively, a combination of...
https://www.marineinsight.com/naval-architecture/marine-exhaust-manifolds/