Heavy fuel oil could make machinery almost self-destructive

Excluding nuclear power, which ship fuel systems were among the most toxic and inefficient?

Some Soviet-era or Russian-region merchant machinery used very heavy fuel oil, leaving engines so burdened by thick fuel and deposits that surveyors regarded them as consuming themselves.

The worst system is not defined only by the nominal energy source. Fuel viscosity, contamination, heating, deposits, and machinery condition determine what crews must endure to keep the plant running. Accounts from ship-survey work describe particularly difficult heavy-fuel-oil installations. The example shows why an apparently economical fuel can become operationally costly when the engine and maintenance system cannot handle it cleanly.