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 Litres/Person/Day

Use Potable Water Wash Water

Drinking Water

Crew, Guests and Passengers

Cooking Water

Cooking and Food Washing

Dish Washing

Washing

Baths

WC’ S

Laundry

Cleaning

Galley

3.2 Litres

3.7 Litres

23.0 Litres

6.8 Litres

36.7 Litres

73.0 Litres

22.7 Litres

4.3 Litres

100.2 Litres

Add 15% to 25% margin for emergencies, excessive consumption,etc.

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.