Aspen C90 Owner's Manual page 8

Sea W ater B all V alves
There are two raw water valves on the boat both in the Starboard
Lazarette (inside hull side fwd). The smaller one ½" is for the head
and the aft deck wash down. The larger one 1.5" is for the engine
cooling water.
Raw Water Valve OFF
½ Inch raw water valve is run typically at 45 degrees to reduce its pressure
while underway and stop head overflow
as running the boat with valves closed will damage the engine and
impellers.
Engine Cooling Water Ball Valve Off
Be sure to close valve when cleaning the raw water strainer
Raw Water Valve On, 45 degrees
.
These valves are typically left on
Engine Cooling Water ON