123. For an OSV operating within U.S. territorial waters, what type of fuel is generally used on auxiliary and main propulsion high speed diesel engines?

Distillate fuel oil is used in high-speed diesel engines on OSVs due to its cleaner composition, lower viscosity, and suitability for the engines' design and operating pressures. Residual and heavy fuel oils are not appropriate for these engines because they require extensive processing and are typically used in larger vessels with specialized equipment.