It goes without saying, boats are not connected to the sewer or water system like we experience at home. Instead, boats store, collect, and take in water for important onboard amenities. Boats have three types or “water systems”, fresh water, grey water, and black water. Let’s discuss how all three systems work.
Fresh Water- Fresh water is stored in plastic tanks built into the boat, commonly these tanks are under a bed or settee and can be anywhere from 10-100 gallons. On a modern sailboat, tanks are +/- 50 gallons and boats above 40’ have two or sometimes three tanks. Since the water tanks are at or below sea level, a 12 volt freshwater pump is used to pressurize the system and deliver water to the faucets as needed. This pump will come on when it feels the pressure drop below a certain level and turn off once the appropriate pressure is achieved. Without an onboard water maker or access to dock city water, these tanks are the only source of freshwater for extended trip.
Grey Water- Grey water refers to water after it has been used. The most common grey waters are from the sink and shower but any water source that is used in some fashion onboard is now considered grey water. For now, grey water is allowed to be drained directly overboard via the boats plumbing. As an example, sink water drains through a P trap and then exists via a thru-hull located below the drain. Sometimes two drains, like the sink and refrigerator, lead to a single thru-hull for reduced build cost and ongoing maintenance.
The other example of common grey water comes from the shower, but this water typically takes a slightly different path. Considering most shower drains are at or below sea level, it would be impossible for the water to use gravity to exit the thru-hull like the example above. Instead, most boats will have a dedicated shower pump the turns on and evacuates the water collecting at the bottom of the shower. Some boats will have an automatic pump with a sensor while others may have a manual switch.
It’s good to keep in mind that everything you put down the drain leads directly to the ocean.
Black Water- Black water comes from the head and simply put… is sewage. Unlike grey water, black water can only be discharged from the boat in certain situations. When the head is flushed, it goes through a hose and eventually makes its way to the black water tank or holding tank. Traditionally, the waste would first pass through a Y-value or diverter value that would send the waste to the holding tank or to the direct overboard thru-hull. That said, it’s common to now see gravity holding tanks that do not require a Y-valve. Explanation of both coming below.
In the US, it is legal to flush black water into the sea given you are more than three miles from any point of land. In this case, one could simple direct the Y-valve to the overboard position, open the head overboard thru-hull, and use the head. If your boat has a gravity holding tank, you simple open the tank outlet thru-hull and the waste will go from the head, straight thru the holding tank and overboard.
Since you are allowed to pump directly overboard while three miles offshore, you are also allowed to empty your holding tank of all waste. If equipped with a gravity tank, you simple open the valve at the bottom of the tank and gravity will take the waste and empty it overboard. If you are equipped with a traditional Y-valve and macerator, it works a little different. In this set up, the holding tank will have a hose that leads to a macerator pump and then to an overboard thru-hull. One would open the overboard thru-hull and engage the macerator pump to empty the tank.
FAQs
The most common culprit is a clogged vent hose or one that's too small for the pump's suction; as a result, not enough air enters the tank to replace the volume of the wastewater being removed. To determine if either of these is the problem, watch the tank (if possible) to see if the sides pull in while pumping.
Where does sewage go on a sailboat? ›
Treated sewage passes through a Type I or Type II Marine Sanitation Devise, or MSD. Depending on the boat set up, the treated waste is then stored in a Type III MSD (holding tank) or discharged directly overboard. Untreated boat sewage may be stored in a Type III MSD or discharge directly overboard.
Can you pump grey water overboard? ›
Per Annex IV of the International Convention for the Prevention of Pollution from Ships (MARPOL), grey water can be directly discharged into most marine environments without further treatment.
How do yachts get rid of toilet waste? ›
The most common setup in new production boats is to have all the waste go directly into the holding tank, which will have a pipe and deck fitting at the top for pumping out shoreside, like most inland waterways craft have.
Why is my water pump not pumping enough water? ›
The water flow can be reduced if the blades are damaged or worn out. To fix this, the impeller should be inspected and replaced if necessary. Air pockets in the water pump can also cause low water pressure. This can be fixed by purging the air pockets through the air release valve.
Why is my boat not pumping water? ›
Check the hoses and connections: Inspect all hoses and connections between the water intake, impeller, and engine for leaks or damage. Make sure all connections are tight and secure. Inspect the thermostat: A malfunctioning thermostat can prevent water from circulating through the cooling system.
What is grey water on a boat? ›
Water from onboard sinks, washers and showers is called graywater. Because boats are not connected to a permanent sanitary sewer system, graywater is discharged directly into the water without treatment.
How far offshore to pump out? ›
Untreated sewage discharges are prohibited within three miles from shore. In order to discharge within three miles, sewage must be treated using a U.S. Coast Guard-approved Type I or Type II MSD. Alternatively, sewage may be stored onboard in a holding tank (Type III MSD).
How often should I pump out my boat holding tank? ›
If you have easy access to free pump-out equipment, then I would fill the tank with water and pump it out once a month if it has seen use. However, if pumping out is inconvenient or costly, waiting longer should not be a problem.
What is black water on a boat? ›
Sewage discharge (also known as blackwater) contains pollutants including nutrients, metals, toxins and pathogens. Blackwater discharged from your boat can impair water quality, negatively affect aquatic ecosystems and increase risks to human health.
The Benefits and Drawbacks of Leaving Your Gray Tank Open:
They highlight the convenience of continuous drainage and the prevention of odor buildup as advantages. However, they also caution about potential issues with clogs and the need for regular tank maintenance when leaving the gray tank open.
Where does shower water go on a sailboat? ›
Because it goes back out into the environment, you must use biodegradable soap, which is usually labeled “no phosphates.” Water from the shower drains either to the bilge or to a dedicated shower sump, and from there it's pumped outside (usually above the waterline).
What are toilets called on yachts? ›
“The bathroom of a maritime vessel is known as the head because of its location aboard vessels in the bow or fore of the ship, as explained by the Naval Heritage and History Command. The term first appears in 1708 in Woodes Rogers' book, “A Cruising Voyage Around the World.” Source Ask.com.
Is bilge water black water? ›
Black water is toilet waste and this raw sewage often contains harmful bacteria and viruses. Grey water is waste water from on board sinks, showers and washing machines. Bilge water is self explanatory but is often contaminated with oil and fuel, and can be a pathway for invasive, non-native species.
Do sailboat toilets flush into the ocean? ›
The main feature of a boat's toilet is that it flushes directly into the water.
How do you clear a blocked marine holding tank? ›
Sometimes filling the holding tank with clean water and agitating the water by chopping the boat can break up materials for their removal. If this doesn't work, add a small amount of liquid detergent and repeat the agitation and flushing process.
Why won't my water pump cut out? ›
If your pressure control switch is faulty (usually a result of clogged tubing or burned contact points), or if someone adjusted the cut-out pressure to be above the pump's capacity, your pump will run non-stop.
What would cause a pump to stop working? ›
This can be caused by various issues, including a broken impeller, a loss of power, or a clogged filter. Pump failures can lead to severe consequences, such as flooding, water damage or complete failure of the piping system, so it is essential to take steps to prevent them.
