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Comment by guidedlight | Hacker News Reader

What problem is solved by using aircraft-style toilets on Navy ships?

Well, the old way to do it is to use sea water flushing which leads to its own problems over the life of the ship with pipes corroding. New(ish) environmental regulations dictate that you can't just flush everything overboard anymore, it needs to be processed through a sewage plant. Despite probably being able to ignore most environmental laws, the Navy normally at least tries to abide by the current laws to be a good citizen and not pollute the oceans as well as having an easier time when visiting foreign ports.

The process plants run better on fresh water but fresh water is expensive and heavy on a ship so a vacuum system allows for less water per flush and really works pretty well if people don't flush stupid things.

Stupid things that my co-workers have fished from sewage plant besides the things mentioned in the article: Towels Screwdrivers Glasses Rags baby wipes/ flushable wipes Pens

As long as only body waste and a small amount of toilet paper are used, the systems are actually fairly reliable. Teaching people that that is ALL that can be flushed is an on going problem. The chemicals seem to be another issue, possibly a design issue but there are ways around that too. Urine crystals build up on the walls of the pipes and reduce the diameter for the waste water to flow. The vaccum systems typically have smaller diameter pipes then the old style "gravity" flush systems. There are companies that make continuous dosing systems that go in the end of the branch lines to help keep them clear.

A lot of issues with maintenance can be solved by design of branches in the piping system with isolation valves so the whole system doesn't have to be shut down to fix something. Even replacing a toilet means shutting off the branch or system since it opens a hole in the vacuum system and leads to loss of vacuum.

Some more information: https://www.boatus.org/clean-boating/sewage/msd-types/

Manufacturers: https://jetsgroup.com/jets-group/the-highest-standards/the-h... https://evac.com/

Actually, good design recognizes that people can't be trusted to follow instructions. Seems even Navy doesn't have enough discipline.

One thing of note: seems the whole system is designed for peace. While I can understand armchair designer (it is likely it will never see something like WWII action) this should be designed as a machine of war in case all hell breaks lose. I guess the backup plan is to have buckets and a bucket brigade...

If all that can be flushed is human waste and paper, then why not put it directly into the ocean? It's quickly and completely bio degradable (eaten by fish and micro organisms).

If the ship is at sea (>12 NM) it can be put directly into the ocean but when it comes close to land it needs to be mashed up and disinfected. Also there are some places called special sea areas that have different rules even if you are more than 12 NM. There are different rules for less then 3 NM and between 3NM and 12NM too.

Having one system for when the ship is out at sea and switching to something else causes even more engineering problems. Even if you're not processing the waste, the vacuum sewage system would still be used to collect the waste to discharge it.

MARPOL Laws: http://www.imo.org/en/about/conventions/listofconventions/pa...

https://www.dco.uscg.mil/Our-Organization/Assistant-Commanda...

Special Sea Areas: http://www.imo.org/en/OurWork/Environment/SpecialAreasUnderM...

When I was on ship, when it was trash day you'd watch them take every trash bag, slit it open, and toss it into the sea.

I wonder if toilets can't be adapted so as to prevent those inappropriate items from being flushed.

For example, suppose that you move part of the "processing" into the mechanism of the toilet itself, i.e. you use some kind of lever-operated press to pass your own output through a sort of a sieve; only soft items will pass, or items you break apart - but then you notice you've broken something apart which demotivates throwing those things in the toilet.

Just a thought.

There’s a substantial number of big passenger ships cruising the seas. One would think this was a solved problem.

Stealth.

Aircraft toilets always sound pretty damn loud to me. And their main reason to exist on planes is the lack of available water. Pretty sure that is not an aircraft carrier’s constraint.

Actually ships are very water constrained. Especially Nuclear as they can't risk sea water contamination to the reactor cooling.

Modern aircraft carriers have reverse-osmosis desalination systems on board. These can supply hundreds (thousands?) of tons of potable water per day.

Yes, fresh water is a valuable commodity at sea; on U.S. Navy ships, water-flushed toilets are flushed with sea water, not fresh — or at least that's the way it used to be, and I can't imagine it'd be different today. (Source: Three years' sea duty as an engineering officer in the aircraft carrier USS Enterprise, CVN-65.)

EDIT: See https://www.navy.mil/submit/display.asp?story_id=103122 for a 2017 press release describing how the Reactor Department produces fresh water aboard the aircraft carrier USS Abraham Lincoln (a Nimitz-class carrier, i.e., an old design). TL;DR: It's done with giant evaporators, that is, distilling units.

Fun fact: At sea, one of the big uses of fresh water aboard a carrier is the repeated washing down of the aircraft to reduce corrosion from the salt air.

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