Sanitary System

Function

• the SANITARY system handles waste water from wash basins, sinks, showers baths, galley equipment as well as waste water from other equipment throughout the vessel.

• Sanitary system is often called the “GREY” water system

Sanitary water content

• Most sanitary water discharges are a fresh water mixture containing residues of cooking oil, fat, soap and/or detergents

• Usually sewage and sanitary systems are maintained separate in terms of tanks, piping and equipment due to health, pollution, and smell considerations.

Regulations

• The discharge of sewage or sanitary water directly into the sea is, like oil, becoming subject to increasingly tighter controls.

• The main Regulations enforcing control are coming from individual countries with respect to their territorial waters.

• The first guidelines is produced by Ministry for the Environment in 1999 and constantly amended

Sanitary water discharge• While the Regulations don’t restrict the

discharge of sanitary water, there are potential adverse effects on the environment created by shower water, galley waste and dishwasher discharge.

• Sanitary water discharges into a tidal stream when an isolated boat is moored short term are not considered to be a problem

• Where many boats are moored in a sheltered bay with very little tidal flow, or an isolated boat is moored long term in sheltered shallow water, the effects are more noticeable

Options:

1. Direct discharge (but United States Coast Guard which are limiting sewage and sanitary water discharge — insisting that holding tanks and or waste treatment equipment is to be fitted to all vessels.)

2. Holding tank and reuse of the grey water for flushing toilets

3. Holding tank and discharge while boat is moving in well circulating waters

4. Use of sewage holding tank

In the smallest of craft

• It is usual that no holding tank is fitted therefore sanitary waste water is simply pumped overboard or if there is sufficient head allowed to drain by gravity.

• It is advisable wherever possible to fit a holding tank for use, at the minimum, when the vessel is in harbour or confined or still waters, when full, the contents of the holding tank may either be pumped ashore through usual sewage/sanitary collection points or discharged in deep water at sea.

• Each line is fitted with a non—return valve to prevent reverse flow and flooding

• Each piece of equipment is connected to the system via a water trap to prevent smells from the sanitary tank

• Equipment drains with insufficient head may require small pumps to be fitted to aid evacuation (e.g. shower trays).

• Care should be exercised when designing the system if to be drained by gravity to ensure that fall/run of pipes are adequate for all degrees of movement of the vessel whether static (trim or heel) or dynamic (pitch or roll).

• Sanitary holding Tanks should be fitted with, at the least, alarms to indicate when they require pumping out, or ideally an alarm combined with the option of an automatic pump out system, either pumped into the sewage or waste treatment plant for processing or overboard.

• Any mechanical or electric tank evacuation pump should be backed up with a manual pump for emergency use when there is no power.

• The evacuation pump system may be shared with the sewage system if necessary providing suitable direction and non—return valves are fitted to prevent unhygienic contamination.

If the simplest of systems is fitted to a small yacht—direct overboard

discharge

• It is important to ensure that the sitting of individual sea—cocks does not cause problems in producing excessive suction when the vessel is moving due to vicinity of propeller race, bow thrusters, other SW, suctions, etc. As well as more seriously the intake of exhaust gases through sanitary outlets causing smell and toxic pollution of living spaces on board the vessel.

What is a water trap?

“S” - trap

Min 300mm

Or

“P” - trap

Failure of water seals in traps

1. Self-siphonage2. Induced siphonage3. Compression4. Evaporation5. Oscillation6. Capillary attraction7. Poor warkmanship8. Momentum

Self-siphonage

• Full bore flow will cause brake of the water seal

• The smaller the bore and the longer the pipes, the greater will be the possibility of the effect

Induced siphonage

• Water flawing past the lower branch pipe tends to draw the air out of the branch pipe and so induce siphonage.

Main branch pipe

Compression

• Compression can occur when previous flow of waste water flows down

Evaporation

• Loss of water seal by evaporation is possible when the sanitary fixture is left without use for a long time

Oscillation

• Water seal can be lost due to varying pressure conditions (wind gusts or atmospheric pressure)

Vent

Varying pressure conditions

Capillary attraction

• Pieces of fabric or hair stacked on the weir can drain water from the trap and break the seal

Momentum

• Water seal removed by momentum caused by long drop

Other considerations

• Materials – expansion allowance (PVC pipes has a high coefficient of expansion)

• Inspection and cleaning eyes to be provided

• Size – fixture’s waste pipe maximum 40mm, main branch pipe size depends on number of fixtures is serves