Watermaker
From Wikipedia, the free encyclopedia
A watermaker is a device used to obtain potable water by reverse osmosis of seawater.
In fact, in the context of boating and yachting, although people popularly refer to `watermakers` the correct description is `desalinators`.
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 tanks for a long passage.
Depending on the design, watermakers can be powered by electricity from the battery bank, an engine, or hand operated. There have been claims of a towed, water-powered watermaker, but these are unsubstantiated.
Contents |
[edit] Water requirement
There is great variation in the amount of water consumed per day. At home in the USA each person uses 140 Lit. of water per day on average.
One Billion people (one sixth of Humanity) have no access to safe drinking water and 200 Million people live on less than 3 Lit. per person per day.
Typical cruising yachts use from 4 to 20 Lit. per person per day, the average probably being about 6 Lit.
The minimum water intake required to maintain body hydration is 1.5 Lit. per day.
The maintenance of comfort under normal circumstances requires 3% of mass body weight or typically about 2.3 Lit. per person of drinking water per day.
The popular brands of yacht watermakers typically make from 5 to 30 Lit. 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:
[edit] Pros
They make you independent of shore-based water supplies. Especially important if you are in a more remote part of the world. They provide safe water when shore-based water is of uncertain quality. Some of the designs are portable and can be converted to manual operation in an emergency. The hand held unit offered by one manufacturer can be used in a liferaft in addition to their normal duties aboard the boat.
[edit] Cons
They are expensive to buy. Costing from $2,000 for the manual type to $10,000 upwards for an engine driven type designed to be fitted to the inboard engine of the vessel.
Some types, but not all, are time consuming and expensive to maintain.
They are very power hungry, except the hand held emergency watermaker.
Some manufacturers have energy recovery systems incorporated in their designs which reduce the power consumption, however these are typically some 50% more expensive for the same size due to their additional complexity. As a guideline, assuming a 12 Volt DC system, the energy recovery incorporated in those watermakers have the effect of reducing the power consumption 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.
[edit] Technology
The technology relies on the principle of Reverse Osmosis. All watermakers designed for small boats and yachts rely on essentially the same technology; a high pressure pump to force 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 mollecules of sodium (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.
[edit] Atmospheric water generator
An Atmospheric water generator is also called a watermaker i.e. a machine that makes pure drinking water from the air.
