My Springer tug, about the same size as your Carol, has no ventilation into the hull. It runs on a Speed 600 motor, direct drive, on two 6 volt SLA batteries in parallel. It turns a 40 mm 3 blade prop. The motor and the ESC get just barely warm to the touch after 1.5 hours' running time, at various speeds.
My Jim Wilder tug has a slightly larger diameter motor of unknown pedigree, which turns a bit slower in direct drive, but on a 12 VDC SLA battery. The prop is about 2", with 3 blades. The cabin has 2 small portholes on each side, with no "glass" in them, so there is some air circulation. The vent arrangement on top of the cabin is arranged to mainly feed air to the smoke generator. Again, no noticeable heating of the motor, ESC or battery.