Your Ship Is Leaking!

Virtually anytime I see a large boat or ship, there’s water pouring out of a hole or pipe not far above the waterline. From tankers to destroyers, carriers and more - they’re all pumping out water.

I’ve always assumed that this was water from the bilge being pumped out, but my question is this: where the hell is that water coming from?

I understand that ships may not have been 100% watertight for the first couple of thousand years, but nowadays? C’mon. Welded steel, fiberglass, plastic shells, all painted and sealed? There can’t be that much condensation, spillage, rainwater, etc., can there?

CPO Dad isn’t around anymore to ask, so I ask you swabbies of The Dope: What’s the poop on the pee from the hole in the hull?

Most likely engine cooling water that is on its way out.

  1. Cooling water - ships typically use a cooling jacket which has external water from the ocean which cools a radiator (or the like) which contains non-salt water.

  2. Waste water - just because it’s clear does not mean there is not poopy in it. Most toilet waste is diluted with ocean water before being pumped out, like 100 gallons to 1 or the like. Also, water from the kitchen, desalinization, etc

  3. The propeller shaft, even though it is sealed, still takes on a little water. As it is rotating it can never be 100% tight even though some systems incorporate pressured air to keep the water out, some still make it in.

  4. And, last but not least, someone has a leaky ship and they are just using the bilge pumps to keep the water out. If it’s a small leak like a crack in the hull somewhere it might be “controlled” and not deemed a risk so they will just pump it out until they are scheduled to go in for repairs.

That is so kewl. I’ve always wondered about that water discharge as well, and never knew this.

For your answer, you should read the boat or ship manufacturing process.

Could be ballast water too: File:Ship pumping ballast water.jpg - Wikipedia

I wouldn’t imagine that it’s cooling water for the engines.

That’s simply because the volume of water is far too little.

I can’t speak for diesel engine ships, but I do know that steam turbines require prodigious quantities of seawater to cool them.
There is a scoop built into the underside of the hull that pulls in seawater into the main condenser. The seawater travels through hundreds of thin tubes, with turbine exhaust steam passing across the outside of these tubes, condensing. After cooling the vapor, the seawater goes back out through a second opening in the hull.

These openings are huge. The shutoff valves for a main condenser are often the largest valves on the ship. It is not unusual for a main condenser inlet or outlet valve to be three feet across.
And the outlet valve is often larger than the inlet valve by an inch or two–to account for the expansion of the seawater as it cools the steam.

There are dozens of other heat exchangers on a typical ship, doing things like cooling oil, providing air conditioning, or even condensing freshwater in the evaporator units. These hull openings are all below the waterline, I believe.

Speaking of which, evaporator units suck in seawater and emit brine + drinking water. Presumably the brine goes out through some hull opening or another.

Ships leak, even new ones (probably especially brand new ones, as they haven’t chased down all the things that haven’t been done up enough or packed well enough). The hull its self is probably pretty water tight but its had dozens of valves and sea-cocks drilled through it and numerous bolts or rivets driven through it.

A question: all this plumbing on board a ship that transports sea water…what’s it made of? Plastic or some kind of PVC? I’m thinking in terms of the corrosive nature of sea water versus most types of metal. Perhaps stainless steel?

As it happens there are three independent plumbing systems in modern ships (according the a naval engineer friend of mine): One for fresh water meant for consumption, one for fresh water not meant for consumption and one for salt water.

On Navy ships, I only saw SS used for special cases such as systems that handled reactor coolant.

Seawater piping appeared to be bronze or monel.

The OP should google “stuffing box”.

When a prop shaft exits the hull and needs to spin, the inevitable consequence is water intrusion, because the shafts exits below the water line.

A good, modern, new stuffing box will leak a little. As it wears, it leaks more. Most ships at sea have hard, long lives, The stuffing box will never be 100% watertight on all those ships.

Brass is a popular ‘through hull’ fitting. Stainless steel is used and sometimes plastic/rubber/etc. When selecting the metal, the decision is sometime limited by the issue that occurs with dis-similar metals (corrosion).

Would have been a great thread title. Or a novelty song.

When in port the main engines will be shut down on most ships.
In port it will not be poop water. That is held insanitary tanks or pumped ashore.
The evaporators will not be running in port. The temperature in low pressure evaps are to low to sanitize the water produced.
But there are plenty of heat exchangers that will be running when in port. HVAC, refridg, aux engines, and so forth.

The setrn tube on a shhip will drip. As the shaft turns in the tube friction is involved. Having a small amount of water always passing through will provide cooling and lubrication.

Any pump with a packing gland will have a small drip where the shaft goes into the pump housing.

Do US Naval vessels have to take on fresh water supplies when in port for drinking water or can they produce their own through desalination? I’ve heard that on the nuclear powered ships, particularly aircraft carriers, that they can and do remain at sea up to six months. How do they re-provision?

They make their own freshwater. Our evaporators could produce 400,000 gallons per day. That said, they still need other consumables such as food, jet fuel, spare parts, and so on. Google “underway replenishment” for details.

They can produce their own water, but I don’t know if they typically do. When pierside in major ports, electricity, telephone, water, and sewage services are available if desired.

However, being pierside is a great time to take generators and desalinization plants offline for maintenance.

For propulsion-fuel, absolutely. For food, not so much. For jet fuel, even less.

The USN excels at this.

All Navy ships make fresh water underway. When pier side, we’ll frequently take on fresh water if we are not running the engineering plant.

Ignorance has been fought this day.

My thanks to you all.

I would also expect that for a ship with heated areas inside, and cold water like the North Atlantic outside, there would be a fair amount of condensation. That would have to run down somewhere inside the ship, and eventually need to be pumped out.