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?
Min 300mm
“S” - trap
Or
“P” - trap
Failure of water seals in traps
1.
2.
3.
4.
5.
6.
7.
8.
Self-siphonage
Induced siphonage
Compression
Evaporation
Oscillation
Capillary attraction
Poor warkmanship
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)
Varying pressure conditions
Vent
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