Understanding Boat Plumbing and Water Systems
by John C. Payne 18 Sep 22:47 UTC
From John C. Payne, one of the foremost international authorities on marine electrical systems and electronics, comes an easy-to-understand yet thorough treatment of boat plumbing and water systems and the technical issues facing every boat owner, whether sail or power.
Concise, compact, and fully illustrated for easy reference, Understanding Boat Plumbing and Water Systems: 2nd Edition has been fully revised throughout. This guide offers a comprehensive coverage of the following major topics:
• Freshwater and saltwater systems
• Hot water systems
• Galley plumbing
• Watermakers
• Bilge pumps
• Shower (gray) water systems
• Sewage (black) water and MSD systems
About the Author
John C. Payne is a professional marine electrical engineer and surveyor, with a career spanning more than forty years in commercial shipping, the offshore oil industry, and yachting. He is a qualified technical writer and author of fifteen marine electrical and electronics books and numerous magazine articles. John has been involved with everything from submarine sonar systems and oil rig operation manuals to military helicopters. Currently, he is a commissioning manager for some of the world's largest and most complex offshore oil production and drilling installations. He has built, restored, and cruised several yachts and lives aboard his own boat in New South Wales, Australia. He is a member of the ABYC and the Cruising Association.
Excerpt
Fresh Water Systems Part 1
Water is the one essential on board any sailing boat. It is a scarce and finite resource and has to be carefully managed. Any boat installation is a scaled back version of a shoreside water utility. Electrical theory often uses the water analogy for explaining systems principles and they have much in common. Other systems that are allied to this include hot water and water makers. The basic elements of a boat fresh water system include water storage and reticulation. A typical basic pressurized fresh-water system is illustrated below.
Water Storage
Water storage tanks have traditionally been manufactured from stainless steel. Depending on the boat manufacturer, they are of varying capacity and location, and retrofitting additional tanks is often challenging. The use of thick-walled high-density PE tanks is now becoming very common. They have fewer leak and corrosion problems than stainless-steel tanks, and they are much lighter in weight. Some boats may use flexible water bladders, and they suit nonstandard shapes and areas. The basic storage system consists of one or, ideally, two water tanks with a water filler cap on deck, with a 1½-inch (38-mm) reinforced hose connecting to the tank. There is also a ½-inch (12-mm) vent overflow that uses reinforced hose connecting to the upper part of the hull with an overboard breather fitting. This arrangement allows air to escape when the tank is being filled with water and in some cases allows excess water to overflow overboard when the tank is full. Ideally the tank should have an access hatch for inspection and cleaning, although on my own boat the previous owner who installed the tank neglected to do so. In addition, a drain valve should be fitted at the lowest point in the tank to allow flushing of sediments, my drain valve has a pipe going to the bilge. Lastly the tank should ideally have some form of contents level monitoring.
Water Tank Level Monitoring
The monitoring of the onboard water tank is essential. A simple electrical gauge that provides the necessary information can be installed, and these have become more sophisticated and smarter. The majority of simple tank sensors in use operate by varying a resistance that is proportional to the tank level using a float assembly. The are a variety of other sensor technologies including optical, radar, ultrasonic and capacitance. For my own boat I recently installed the innovative Gobius system with externally mounted sensors on my fuel, black water and freshwater tanks. The Gobius sensors are installed on the outside wall of the tank and can measure through plastic, fiberglass, and also metal, including stainless steel up to a certain thickness (around 3 mm). The system has two active components: the exciter and the accelerometer. A vibration with a one-second duration is created by the exciter on the tank wall. The accelerometer measures the vibration caused by this force and then transmits the signal to a processor. The algorithm within the processor calculates a value each time the sensor measures. When fluid is over the sensor tank area, this causes vibration values to alter when the fluid level is detected. Head to gobiusc.com for details. The Tank Tender from Hart Systems is a pneumatic system and has been well proven over the years on cruising yachts. It can monitor up to ten water and fuel tanks. It works by using air pressure, which is pumped through a nylon tube from the instrument to the tank being measured. When the air pressure in the tube inside the tank equals the liquid pressure at the tank bottom, the gauge displays this pressure in inches of tank liquid. The measurements are very accurate. Check them out at tanktender.com.
About Water-System Piping
Flexible hosing is commonly used for onboard water systems and is reinforced to prevent it from collapse due to water-suction pressures as well as bursting due to water system pressure. Hoses are usually reinforced with a woven polyester braid. When used in potable-water installations, the hoses should be of high-quality food-grade material that has been approved by the FDA or the equivalent, as this approval signifies that the hoses are made from nontoxic compounds. Approved hoses should not be able to support microbiological growth. Ideally, the hose should have a temperature range to suit both hot and cold water and must be capable of withstanding the water-system pressures. Ratings and approvals are usually printed on the piping exterior.
Water-System Pipe Installation
When water piping is installed, the longer the run, the larger the pipe that is required. Increasing the size of the pipe reduces the friction losses that occur inside the pipe. The runs should be as straight as practicable, without any sharp bends or kinks, as these create resistance to water flow, not unlike electrical resistance. All potable-water piping, when installed low down, below water level or within bilge areas, should be installed above the maximum anticipated bilge water level. Consideration should be given to potential contamination and the effects of oil and other bilgewater material on the piping and any system connections and fittings. There are water-system fitting acronyms that include BSP (British Stand Pipe), which is used in the United Kingdom and many other locations, and NPT (National Pipe Thread), which are tapered pipe threads used in the United States; pipes made according to one system or the other need to be either adapted or converted in some cases. While piping is somewhat resistant to freezing, it can still occur. It is always best to have a drain valve installed at the lowest point in your system, and, before winter sets in, drain down the system. Freezing can burst the piping and seriously damage the connection fittings.
About Semirigid Piping
The use of semirigid PE (polyethylene) piping has grown. It has the advantages of having good chemical resistance and good flexibility, being nontoxic and easily connected and disconnected, and covering a wide temperature range. It has a rating of 100 psi (7 bar) at 180°F (82°C) and 160 psi (11bar) at 72°F (22°C). The Whale Quick Connect system and the John Guest Speedfit are the best-known systems. These systems are excellent, and I used the Whale system on my own boat water system refit. Used together, they create a color-coded semirigid pipe system in which pipes are red for hot, blue for cold, and green for saltwater such as a washdown system. This piping uses push-in fittings to join or terminate pipe into fittings. The push-in fittings comprise a collet, a grip ring, and a rubber O-ring seal. To install, a special cutting tool is required for preparing the tube ends. This tool is essential for clean tube cutting; hacksaws are not good enough. Simply slide the prepared tube into the fitting, and push until the end of the tubing seats firmly against the internal stop. When installing a push-in fitting, ensure that the pipe is not kinked, and, where tight bends are required, install a bend. Like electrical cables, piping has minimum bend radii that should be adhered to. It is important to observe what your PE fittings materials are. The various thermoplastics include Acetal, PE, PP (polypropylene), and PSU (polysulfone). The latter should not be exposed to pipe dopes, lubricants, cleaners, thinners, hydrocarbons, and paints, so keep it installed away from bilgewater. Manufacturers include Whale (whale.navico.com), John Guest Speedfit (www.johnguest.com), PEXtite (pextite.com).
About Piping And Hose Support
Many of these measures are the same as in supporting electrical cables; piping requires protection from mechanical damage and heat damage. Use pipe clips to support the tubing, and fix them at maximum intervals of around 24 inches (610 mm). Smaller intervals are better; I prefer every 12 inches (300 mm). Clips closest to fittings should be no more than 6 inches (150 mm) from the fixture. Where piping or tubing transits bulkheads or any other point, install grommets or sleeves to prevent any chafe and do not run tubing or hoses close to any heat source. If you do choose to install flexible hoses for water distribution install away from sunlight. Ensure that hose clamps are properly sized and secured correctly without overtightening. I recommend you install hose clamp end guards from Clamp Aid to the stainless-steel tails to prevent accidental cuts. Go to www.clamp-aid.com.
About Water Pressure Pumps
The primary purpose of the water pump is to pressurize the water distribution system from the water tank and supply to all the outlets. A pump is selected based on the number of outlets to be supplied and the flow rate required. If the pump is incorrectly rated for the system, the flow will drop off when another outlet is opened. Diaphragm pumps are most commonly used and are robust and designed for multi-outlet high-pressure water systems. They are more tolerant of dry running conditions, are self-priming, and are relatively quiet in operation. Pressure switches are usually built into the pump. These multi-chambered pump units have improved suction, less water pulsation, and have a more stable water flow.
About Water-System Strainers
The water strainer is installed in the water suction line to the pump. The primary purpose is to protect the pump from damaging sediment and particles being suctioned from the water storage tanks. It is essential that the stainless-steel element be inspected and regularly cleaned. Blockages are most frequent on commissioning of a new vessel or after refilling an empty tank. I have seen numerous vessels in which the element has been removed because the boat owners were tired of cleaning blockages. The result will be early pump failure. It is good practice to clean the system and eliminate the cause. After cleaning the element, ensure that a good seal is made with the transparent inspection cover, as a poor seal is a common cause of air being drawn into the system but do not over tighten. Ensure that the seal is in good condition.
About Water System Accumulators
The accumulator is an important part of a water system. The basic principle is that air will compress under pressure and the water will not. The accumulator is a tank filled with air that fills to approximately 50 percent with water when the pump operates. After the pump stops running, the compressed air provides pressurized water, stored within the accumulator. It serves two functions, the first being a pressure buffer or cushion that absorbs fluctuations or spikes in pressure. This pulsation is an inherent characteristic of diaphragm pumps. The effect is to operate quietly, and the pump pressure switch is able to reach the cutoff pressure, which increases the life of the pump, the motor, and the pressure switch. The second function is pump cycling. The life of the pump is extended, as the accumulator will prevent the pump from operating as soon as the water outlet is opened. If a large accumulator is installed, the pump will operate less; where large-demand systems are installed, larger accumulators are required.
Troubleshooting Water Systems
The following are typical and common faults that you might encounter;
The water pump does not run. The pump circuit breaker has tripped off, if so the water pump is possibly seized or there is a faulty pump connection. The pressure switch can also be faulty.
Pump runs, but no water is pumped. The water tank suction isolation valve is closed; the water tank is empty, the water inlet filter is clogged, if fitted the check valve is seized, the pump diaphragm is damaged, or there is debris trapped in the diaphragm, there is a leak on the pump suction side drawing air in, or if installed an outlet valve is closed.
Excessive or frequent pump cycling. The system has a pressure leak, a water outlet is leaking or there is an accumulator charge problem.
Pump will not switch off. The water tank is empty, the pump diaphragm is ruptured, there is a major leak on the discharge line, the pressure switch is faulty.
This article was extracted from Understanding Boat Plumbing and Water Systems and The Marine Electrical and Electronics Bible 4th Edition by John C Payne.