The large hose hanging down is for bilge ventilation. Usually, the hose bringing in fresh air is up high and the one that's connected to a fan motor goes down low. This is to suck out gas fumes since they settle at the bottom (heavier than air). You're supposed to run the fans for 5 mins before you crank eng/s and when going slow but most people don't.

A lot of times the hose bringing in fresh air is connected to louvers (on the side of the boat) that face into the wind forcing air into bilge to feed engs and provide ventilation.
Louvers facing rearwards should be connected to lower hose/s to help draw out fumes when underway. That way you don't have to run the bilge fan when cruising..

Have no idea what was mentioned here but before you get after it I would check for transom rot and stringer rot. In one pic at the drain plug is that a rotted wood stain running out of it and down ?

You need indicator cables - the outer is tearing apart. Also is that a white silicone bead line around the transom assemblies to transom seal ? If so that usually is a sign of a water leaking transom and the boat owner bandaide to stop the water leaking and or stop it while its for sale.

Its had a 6 to 8 inch water line in the boat for while - brown staining all over in the engine compartment. Also in the bottom right corning check for rot in this pic. You see the brown water line in this pic as well, That bottom right corner looks like possible rot and where that hose area is coming thru.https://cimg8.ibsrv.net/gimg/www.off...fb2046e597.jpg
in the pic below