Fresh water system
Matter to be decided:
• Potable water
• Wash water
Pressure in the system: usually 10 to 40 psi
69 to 275 kPa
0.69 to 2.75 bar
Pressure set
is a unit consists of:
• Pump (usually displacement type)
• Accumulator tank
• Pressure switches: high and low pressure
Accumulator tank
Accumulator tank benefits:
• Absorbs the pulsations in supply from the
pump (works as air vessel)
• Extends pump life
• Reduces battery drain
Choice of the pressure set
• Decide how many outlets you require
• What flow is required from each outlet
(from manufacturer specification)
• Estimate how many outlets will be opened
simultaneously
• Decide your maximum normal flow
requirement
• Choose the pump according to that flow
and the chosen pressure
Carbon based water filter
• Filters, freshens and cleanses stored
water to give a fresh, clear, natural taste
• Activated carbon removes unpleasant
tastes, smells and colours, including
chlorine
• Removes suspended dirt, sediments and
fibres
• Silver impregnating inhibits bacterial
growth when not in use
Water heaters (Calorifiers )
• Heat Transfer – cooper coils with engine
cooling water, heat accumulator
• Electric Elements -The rating should not
exceed 1200-1800 watts, thermostat is required
• Calorifier Valves –
non-return valve
pressure relief valve
drain tap
• Insulation - polyurethane foam, some
companies quote a 0.5°C loss per hour
• Installation - The calorifier should be mounted
on the same level as the engine cooling water
source or below
Diesel Hot Water Heaters
Instantaneous water heater
• Electrical – 6kW for shower – 3 Litres/min
• LPG
If the choice is LPG read installation
requirements on boats. Web info:
•
•
•
http://www.insightmarinesurveyors.co.uk/gas.htm
http://www.gaslow.co.uk/pages/marine.htm
http:// www.yachtworks.net/propane_installations.htm
Fresh water tanks
Integral in mild steel, aluminium, GRP or wood
vessels then the tank internal surfaces need to
be coated with an epoxy based paint
approved for drinking water use.
Separate tanks. The tanks may be constructed
from any material if internally coated.
Usual practise is to use stainless steel (A1S1
316L) which, like purpose built GRP separate
tanks (with GELCOT on the inside) do not
require coating internally.
Water consumption
Use
Litres/Person/Day
Potable Water
Wash Water
Add 15% to 25%
margin for emergencies,
excessive consumption,
etc.
Drinking Water
Crew, Guests and Passengers
3.2 Litres
Cooking Water
Cooking and Food Washing
3.7 Litres
Dish Washing
23.0 Litres
Washing
Baths
73.0 Litres
WC’ S
22.7 Litres
Laundry
4.3 Litres
Cleaning
Galley
6.8 Litres
36.7
Litres
100.2 Litres
All tanks should be supplied with
the following:
• (a) Filling pipe work of adequate size,
• (b) Air ventilation pipe led as high above the main deck
as possible, incorporating a swan neck and mesh filter,
• (c) Manual sounding tube for dip stick use to check
capacity of tank,
• (d) Tank outlet to be of sufficient size and led from point
of tank via internal pipe if necessary,
• (e) Suitable fitting for remote sensing of tank levels
(electric, mechanical or pneumatic),
• (f) Inspection man-hole of suitable size to allow visibility
and access
• (g) To be appropriately baffled.
Fresh water tanks location
• double bottom or bilge area obviously to
maintain a lower VCG and maybe divided
fore and aft to supply the accommodation
in the ends of the vessel
Some rules and considerations
1. Install the pump as close as possible to the
water supply tank, consistent with a dry,
ventilated & accessible location.
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Some rules and considerations
2. Keep suction pipework as short and straight
as possible with minimum suction lift. Use rigid
pipe or reinforced hose that will not deform or
collapse under suction conditions. Ensure that
all connections are airtight.
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Some rules and considerations
3. The internal diameter of the suction pipe
should be at least as large as the nominal bore
of the pump ports.
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Some rules and considerations
4. Fit a suction line strainer between supply tank
and pump. Make sure that it is accessible, and
remember to inspect it periodically.
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Some rules and considerations
5. Avoid transparent / translucent pipework,
which is susceptible to algal growth./
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Some rules and considerations
6. Use discharge pipework of adequate size —
13mm (1/2”) internal diameter in small systems.
In larger vessels, use 13mm (1/2” branches to
taps etc. from a 19mm (3/4”) or 25mm (1”) main
pipe running the length of the vessel.
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Some rules and considerations
7. Check that pump cut-out pressure is suited to
all other system components, e.g. calorifier.
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Some rules and considerations
8. Always fit an accumulator tank — the larger
the better.
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Some rules and considerations
9. After refilling an empty supply tank, open one
outlet before switching on the pump. This allows
the pump to re prime itself rapidly..
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Design details to be considered when
developing a freshwater system are as
follows:
• Bolted connections should not be made through
the shell of potable water tanks,
• Pumps, manifolds (filling, transfer, and suction),
and gauges should be grouped,
• Potable water services should be grouped to
keep the number of branches from the main to a
minimum,
Service branch sizes should be based on the
number of fixtures installed.
• All risers exposed to the weather should have
means for draining to prevent freezing,
• Potable water piping should not be run through
bilges.
• All branch connection to the main freshwater
system should be provided - with stop valve,
• A non-return valve should be installed in the
supply to water heater, to prevent hot water from
backing up in the cold water piping,
• Gauge glasses should have guards, or be
otherwise protected against accidental breakage
In addition
• Additional requirements regarding freshwater
systems are contained in the regulations of the
Public Health authority involved. A thorough
understanding of these regulations should be
obtained before undertaking the design of a
freshwater system for commercial and
passenger vessels.
• In these cases fresh water supplied for drinking
and culinary purposes must meet purity
standard specified by the Department of
Transport. Water produced from most
evaporator/distillers will not meet these
standards and must be treated to ensure it is
biologically pure and neutral or slightly alkaline.