Watermaker
Encyclopedia
A watermaker is a device used to obtain potable water by reverse osmosis
of seawater. In boating and yachting
circles, desalinators
are often referred to as "watermakers".
s for a long passage.
Depending on the design, watermakers can be powered by electricity from the battery bank, an engine, an AC generator or hand operated. There is a portable, towed, water-powered watermaker available which also converts to hand operation in an emergency.
, each person uses about 55 Gal. of water per day on average Virginia GPCD. Where supplies are limited, and in emergencies, much less may be used.
Typical cruising yachts use from 4 to 20 litres per person per day, the average probably being about 6 litres. The minimum water intake required to maintain body hydration is 1.5 litres per day. The maintenance of comfort under normal circumstances requires 3% of mass body weight or typically about 2.3 litres per person of drinking water per day.
The popular brands of yacht watermakers typically make from 2 to 150 litres per hour of operation depending on the model.
There are strong opinions among small boat cruisers about the usefulness of these devices. The arguments may be summarised as:
The drawbacks for these non-electric designs are that manual operation is tiring for the operator and the towed watermaker only works while the vessel is moving through the water.
Some manufacturers of electrically powered watermakers have energy recovery systems incorporated in their designs which reduce the power consumption; however, these are typically some 50% more expensive for any similar size due to their additional complexity. As a guideline, assuming a 12V DC system, the energy recovery incorporated in those watermakers have the effect of reducing the electrical current used from perhaps typically 20A to about 8A.
The common comparison is that of a filter; however, as the holes in the membrane are smaller than molecules of sodium chloride
(salt) and indeed smaller than bacteria, and pressures in the nature of 68 bar
are required, the process is much more complex than the common water filter or the oil filter found in our automobile engines.
, a machine that extracts pure drinking water from the air by refrigeration
. These are, however not energy efficient in comparison to reverse osmosis technology. Their great advantage is that there is no water supply required as they obtain the water from the atmosphere. The drawback is that they require some amount of humidity in the air & a certain range of temperature. Contrary to the general perception, an AWG will function & produce water even in a desert (although may produce 1/2 its capacity) on account of the dew point
factor at night.
Reverse osmosis
Reverse osmosis is a membrane technical filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and...
of seawater. In boating and yachting
Yachting
Yachting refers to recreational sailing or boating, the specific act of sailing or using other water vessels for sporting purposes.-Competitive sailing:...
circles, desalinators
Desalination
Desalination, desalinization, or desalinisation refers to any of several processes that remove some amount of salt and other minerals from saline water...
are often referred to as "watermakers".
Varieties
Many different versions are frequently used by long-distance ocean cruisers. The devices can be expensive to buy and maintain, but are a huge advantage because of the reduced need to have large water tankWater tank
A Water tank is a container for storing water. The need for a water tank is as old as civilized man, providing storage of water for drinking water, irrigation agriculture, fire suppression, agricultural farming, both for plants and livestock, chemical manufacturing, food preparation as well as many...
s for a long passage.
Depending on the design, watermakers can be powered by electricity from the battery bank, an engine, an AC generator or hand operated. There is a portable, towed, water-powered watermaker available which also converts to hand operation in an emergency.
Water requirement
There is great variation in the amount of water consumed per day. At home in the United StatesUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, each person uses about 55 Gal. of water per day on average Virginia GPCD. Where supplies are limited, and in emergencies, much less may be used.
Typical cruising yachts use from 4 to 20 litres per person per day, the average probably being about 6 litres. The minimum water intake required to maintain body hydration is 1.5 litres per day. The maintenance of comfort under normal circumstances requires 3% of mass body weight or typically about 2.3 litres per person of drinking water per day.
The popular brands of yacht watermakers typically make from 2 to 150 litres per hour of operation depending on the model.
There are strong opinions among small boat cruisers about the usefulness of these devices. The arguments may be summarised as:
Pros
- The user is independent of shore-based water supplies, which is especially important in remote parts of the world.
- They provide safe water when shore-based water is of uncertain quality.
- Some designs are portable and can be converted to manual operation in an emergency.
- The hand-held unit offered by one manufacturer and the towed water-powered watermaker offered by another manufacturer can be transferred to a liferaftLifeboat (shipboard)A lifeboat is a small, rigid or inflatable watercraft carried for emergency evacuation in the event of a disaster aboard ship. In the military, a lifeboat may be referred to as a whaleboat, dinghy, or gig. The ship's tenders of cruise ships often double as lifeboats. Recreational sailors sometimes...
in an emergency.
Cons
- They are expensive: indicative costs are US$United States dollarThe United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
2,000 for the manual type, US$United States dollarThe United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
3,000 for the towed water-powered type, US$United States dollarThe United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
4,000 or more for an engine-driven type, designed to be fitted to the inboard motorInboard motorAn inboard motor is a marine propulsion system for boats. As opposed to an outboard motor where an engine is mounted outside of the hull of the craft, an inboard motor is an engine enclosed within the hull of the boat, usually connected to a propulsion screw by adriveshaft.-History:The first...
of the vessel, and about the same for an AC generator-driven type. - Some types (but not all) are time-consuming and expensive to maintainMaintenance, Repair and OperationsMaintenance, repair, and operations or maintenance, repair, and overhaul involves fixing any sort of mechanical or electrical device should it become out of order or broken...
. - They are very power hungry, except the hand-held emergency watermaker and the towed water powered type. Accordingly, these devices overcome the problem of large electric current demand.
The drawbacks for these non-electric designs are that manual operation is tiring for the operator and the towed watermaker only works while the vessel is moving through the water.
Some manufacturers of electrically powered watermakers have energy recovery systems incorporated in their designs which reduce the power consumption; however, these are typically some 50% more expensive for any similar size due to their additional complexity. As a guideline, assuming a 12V DC system, the energy recovery incorporated in those watermakers have the effect of reducing the electrical current used from perhaps typically 20A to about 8A.
- Like every additional piece of equipment, it is bound to fail at some time in the future and cause expense/anxiety.
Technology
All watermakers designed for small boats and yachts rely on essentially the same technology, exploiting the principle of "reverse osmosis"; a high pressure pump forcing seawater through a membrane which allows water but not salt to pass.The common comparison is that of a filter; however, as the holes in the membrane are smaller than molecules of sodium chloride
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
(salt) and indeed smaller than bacteria, and pressures in the nature of 68 bar
Bar (unit)
The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...
are required, the process is much more complex than the common water filter or the oil filter found in our automobile engines.
Atmospheric water generator
Another type of watermaker available is the atmospheric water generatorAtmospheric water generator
An atmospheric water generator , is a device that extracts water from humid ambient air. Water vapor in the air is condensed by cooling the air below its dew point, exposing the air to desiccants, or pressurizing the air. Unlike a dehumidifier, an AWG is designed to render the water potable...
, a machine that extracts pure drinking water from the air by refrigeration
Refrigeration
Refrigeration is a process in which work is done to move heat from one location to another. This work is traditionally done by mechanical work, but can also be done by magnetism, laser or other means...
. These are, however not energy efficient in comparison to reverse osmosis technology. Their great advantage is that there is no water supply required as they obtain the water from the atmosphere. The drawback is that they require some amount of humidity in the air & a certain range of temperature. Contrary to the general perception, an AWG will function & produce water even in a desert (although may produce 1/2 its capacity) on account of the dew point
Dew point
The dew point is the temperature to which a given parcel of humid air must be cooled, at constant barometric pressure, for water vapor to condense into liquid water. The condensed water is called dew when it forms on a solid surface. The dew point is a saturation temperature.The dew point is...
factor at night.