You seem to think it has a hose from the thruhull from the motor
but you didn't actually say so. I would start by tracing the hose to its origin. If it is the motor
, you will be able to tell right away what it could be doing, if from nothing else than the engine
manual/diagram and at least a basic understanding of marine
I was crew on a boat I had never been on and water started blowing in to the cockpit
all of a sudden - like 3-4 gal in just a couple of minutes. Emergency! The skipper
had never bothered to even look at that specific part of the boat (I literally could not believe this) and had no idea where it was from. Turns out is was from a bilge pump
he didn't know he had. AND, the engine
and water was coming out of the fresh water tank
from the badly-in-need-of-replacement cap. He knew the engine overheated regularly but never mentioned that to me before we left. He thought it was normal. I left the boat at the next stop.
It could be a bilge pump
outlet on your boat. I'd recommend you do a complete survey
of all thruhulls and know what they are for and make a diagram and put it in a safe place to look at when you need to. If you haven't done that already you should also thoroughly inspect the hose clamps and hoses as to their condition. If in doubt replace asap.
Just some thoughts. It would be good to check out all of this stuff. It will also lead you to find other stuff you didn't even know you have. I always do until I have surveyed 100% of a new boat.