On larger scale high performance RC boat the rudder often serves as the water inlet. The rudder is heavier and the inlet is small, but due to the high speed there is still going to be sufficient water moving into it.
Some smaller high end boats also use rudder that also serves as water inlet (even though it is less common due to cost concern):
It is recommended that you change the water outlet (heated water leaving the system) to a visible location like what is shown in this photo. This allows you to easily monitor cooling and make sure nothing gets stuck along the water cooling path.
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