why do large boats have spouts near water level that continuously dump out water?
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Bilge Pumps (pumping over excess water in the bottom from leaks)
AC Pumps (Pumping water in an out for cooling)
AC condensation drains. Your car does this, but it just dumps the water onto the ground.
Engine pumps (water in and out for engine cooling)
Generator engine pumps (water in and out for engine cooling)
Grey and black water draining – Shouldn’t ever see that at dock (big fines), but they do open up at sea. Dishwater, shower water, toilets etc.
Large boats and ships have a whole lot of systems that use water. It could be any of those systems, although some of the systems that use really large amounts of water aren’t going to have a discharge visible above the waterline (thinking things like variable ballast) some of the systems have to be above the waterline for service connections to take over when the ship is moored (thinking things like sanitary connections) and some are almost always going to discharge into the water because the volume is small and the use is infrequent when moored like engine cooling water. Fresh water usually isn’t discharged directly overboard not for environmental reasons, but because there’s usually not a need to discharge it overboard. You run the freshwater plant (still, RO, whatever) until you’ve filled the tanks that store the water they produce, then you shut the plant down until the level gets down to wherever they’ve decided it’s time to run the plant again. The flushing water from the other side is discharged overboard but the amount of bad stuff leftover from purifying the seawater being added to the ocean in various places as the ship or boat moves along is course is relatively miniscule. There are certain things you can’t discharge overboard although I wouldn’t say they’re never discharged but there are big fines if anyone is discovered pumping something like waste oil overboard
They shouldn’t be consistently dumping water out but that is the intended purpose of it. Boats go on water and try as you might, inevitably some water ends up inside the boat. This all flows to the lowest point inside the boat. If you didn’t get it out, eventually you’d have enough water to destroy/sink your boat. Back in the old days they’d use buckets to dump it over the side trying to keep as much out because obviously you’d don’t want water inside your boat.
Today we have electronics and such, so we don’t have to do it manually. Instead we have what is called a bilge pump! So it sits at the lowest point in the boat in an area thats designed for the water to flow to it. When you turn the pump on, it pumps the water from inside the boat to outside the boat. This keeps minimal amounts of water inside the boat instead of it accruing over periods of time.
It’s over the water line by design. If it was under the water line then the water would flow into the pump which could be designed to keep it from entering, but then when it worked it would have to push the water inside with more force than the water on the outside coming in. It’s just easier to put it above the water line so there’s no water resistance coming in and it can flow unimpeded besides gravity.
Often times a boat like mine it is automatic. When the water reaches a certain height this triggers the pump to turn and it runs until it goes below a certain height. This isn’t some crazy big expensive boat, but a little 19 foot wakeboard boat. Bilge pumps are standard equipment on most boats these days. Since mine is a little river boat that only sits like 6 inches out of the water, having a little water get into the boat over the side isn’t that rare. It’s not a concern though because whenever my boats in the water I keep my pump on so it doesn’t accrue too much and it pumps when needed.
If a boat is continuously pumping water out, that is an issue though. That would mean the boat was taking on more water than it could pump out and it would eventually sink. That boat is immediate need of either A figuring out why it’s taking on so much water and fixing it. Like is there a hole in the boat letting water leak in? Or B if there isn’t a major issue letting water in then it means the pump isn’t big enough and can’t flow out the amount of water necessary. They need to either install another bilge pump to help it or they need to upgrade the one they have to a bigger more capable unit.
You’re seeing sea water discharge. Sea water is sucked up from sea chests at around the bottom of the hull, circulated to use for cooling systems such as reduction gears and engines, and then discharge overboard.
When you say “continuous”, I assume you mean even when the engine(s) isn’t running. That’s most likely for the A/C. Since you said boats and not “ships”, I assume you’re talking about pleasure boats you’d see in a marina. Those boats often have an onboard air conditioner that when operating pulls water in, cools the ac then pumps it overboard. You know how central air for a home has a big unit outside with a giant fan? Same thing, but on a boat there’s no room for the big fan cooled unit, and no need for it since a boat has endless cooling water available to it. You may also see another constant stream of water if the boat has a generator and it’s running. Same reason. Cooling water. No need for a radiator since you can just pull in lake or river water. And since the generator is mounted in an enclosed engine compartment, air cooled wouldn’t work. Most of the other answers you got are correct, the engines of the boat also suck up water and expel it out the exhaust but you won’t see it on most boats because that’s happening underwater. Unless the boat has through hull exhausts. Source: My boat has a/c, a generator and through hull exhausts.
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