Boat plumbing is a lot easier for the do-it yourselfer than plumbing at home, mainly because it doesn’t involve rigid pipes running inside solid walls. In fact, pipes are rarely used at all on boats, replaced by easier-to-handle flexible hose or tubing.
Here is an overview of a typical on-board water system.
Because water is heavy, tanks should be mounted low in the boat. Where space is available, it is a relatively simple matter to add extra tanks. Rigid polyethylene tanks are available in hundreds of shapes and sizes, or you might use a flexible bladder tank–essentially a water bag. Water tanks typically have three threaded ports, one for the outlet and one for the vent hose, both 1/2-inch, and one for the fill hose, usually 1 1/2-inch. Threaded hose barbs allow for hose connections. The inlet is connected to an on-deck fill. (Be sure the deck-fill has an O-ring to seal out seawater when it is closed.) The vent line leads to a vent fitting high in the boat– above the tank at every expected angle of heel. Be aware that if the vent is not also higher than the fill, it will overflow when you are filling the tank. The outlet connection leads directly to a pump or, in a multi-tank installation, to a manifold or Y-valve.
Use Teflon tape or thread sealant on all threaded fittings, and don’t over tighten fittings in plastic tanks. Secure hoses with stainless steel hose clamps.
Supply piping for a boat water system must be non-toxic, non-contaminating, taste-free, and FDA approved for drinking water. If the system is pressurized or will carry hot water, the piping needs to be suitable. The traditional choice for water system plumbing has long been clear PVC reinforced with polyester braid. This same type hose can be used for tank fill and vent connections.
In recent years semi-rigid polyethylene (PE) tubing, long used in RV plumbing, has surged in popularity for boat plumbing. It has much to recommend it. With quick-connect fittings, a PE tubing water delivery system assembles with the simplicity of Tinker toys. The opaque or at least semi translucent nature of the PE tubing discourages algae growth that can be a problem with clear hose. PE tubing also comes in colors–typically red for hot water and blue for cold–which looks nice and might make plumbing failures easier to trace. Because the tubing is less flexible than PVC hose and it must be cut to the correct lengths, a PE plumbing system will be slightly more demanding to install. However, the primary negative to PE plumbing is the cost of the fittings, which at this writing run $4 to $8 each. On the positive side, the tubing is actually cheaper than reinforced clear PVC hose.
Drain hoses connected to through-hull fittings should be stronger than clear vinyl hose. For this use, select reinforced rubber hose, sometimes called heater hose. This is the same type of hose used on engine plumbing, and it typically has about three times the burst strength of reinforced vinyl hose. Double clamp all hoses connected to through-hull fittings.
Water pumps on a boat can be either electric or manual. An electric pump pressurizes the entire water system. Most electric pumps have a pressure switch that activates when the pressure drops below a set value–usually around 30 or 40 PSI. Opening any tap on the boat releases pressure and causes the pump to kick on and run until it rebuilds the pressure to the cutout setting. The pump cycles on and off until the tap is closed. The inlet of an electric pump connects directly to the tank outlet (or multi tank valve), and the outlet supplies water to all faucets and appliances.
Manual pumps–hand or foot operated–supply a single spigot connected directly to the outlet side of the pump. A regulating valve is not required; water flow is controlled by the operation of the pump. The primary advantage of manual pumps is that they dramatically reduce water waste, a major concern for boats that spend long periods away from water supplies.
Some water systems include an accumulator. Large accumulators have pressurized bladders in them, but most small ones are just empty tanks teed into the line downstream of the pump. When the pump runs, it tries to fill the tank from the bottom, compressing the air trapped inside the tank. The pressure from the tank allows small amounts of water to be drawn without the necessity of the pump running, thus reducing pump cycling.
A marine water heater is simply a small, insulated tank downstream of the pump. You must have a pressurized water system to operate a water heater. The pump draws water from the storage tank(s) and fills the water heater tank. Inside the water heater is an electrical heating element and usually a coiled tube called a heat exchanger. When AC power is available, the electrical element (controlled by a thermostat) heats the water. Away from the dock, the hot engine coolant is routed through the coiled tube to heat the water in the tank when the engine is running.
Water heaters have four threaded ports. The tank inlet connects via a tee- connector to the outlet hose from the pump. A check valve is required in this line or in the heater to prevent hot water from migrating back toward the pump. The outlet connection supplies heated water to the hot side of all faucets, also using tee-connectors. The other two ports are for the heat exchanger connection, which varies depending on engine installation. Use only metal fittings to plumb a water heater, never plastic. If a pressure- release valve isn’t integral, the heater will have a fifth port for this essential component.
Faucets are the ultimate terminus for water system lines. Manual pumps require simple spigots, but in a pressure water system, boat faucets differ from those found ashore only in styling and that they may be fitted with hose barbs. Mixer faucets require two connections, one from the cold side to the supply line from the pump and the other from the hot side to the water-heater outlet.
Shower connections are identical to faucet connections. The only difference is that rather than delivering the water through a spigot, the water is delivered through a pipe or hose to the shower head. A nice owner addition to almost any boat is a deck shower, easily installed by simply teeing into cold- and hot-water supply lines.
Sink drains typically connect with reinforced rubber hose to a through-hull fitting. On a sailboat, sinks are best located near the centerline of the boat so heeling doesn’t put them below the waterline. Because head sinks are often well outboard, they may be plumbed to drain into the bowl of the toilet to avoid the risk of flooding. There are collateral benefits of running fresh water through the head.
Shower pans too often drain into the bilge to be pumped overboard by the bilge pump. However, this arrangement eventually leads to unpleasant bilge odors, and it risks jamming the bilge pump with hair.
Shower pans should be isolated from the bilge and include a discharge pump, either automatic or connected to a switch. The through-hull discharge outlet must always remain above the water.
Since few boats carry sufficient fresh water to allow washing the decks with it, wash-down pumps are not connected into the freshwater system. Nevertheless, a wash-down pump is a great convenience for hosing the deck and knocking mud off the anchor chain.
The inlet fitting of a wash-down pump is connected to a submerged through-hull fitting, and the outlet side is connected to a deck-mounted faucet or male hose connector. A dedicated through-hull is not required; if you are installing a deck wash pump; use a Y- or tee-connector to tie into an existing inlet line. Use heavy-duty rubber suction hose, wire reinforced to keep the hose from collapsing. Debris will damage or destroy a wash-down pump, so it is essential to have a strainer in the intake line.
On-board air conditioning in some climates is fast becoming a necessity rather than a luxury and can mean the difference between an uncomfortable and enjoyable cruise. Whether buying an air conditioning system for the first, second, third or tenth time, outfitting a boat with the latest gear should be part of the fun, not a chore.
Do I need one?
Don’t be fooled by the common misconception that air conditioners simply cool the air – there’s a lot more to it. In colder climates, quality A/C systems can also provide year-round heating. In addition to cooling, air conditioning systems also control humidity, which is high when in close proximity with water. Marine air conditioning removes moisture from the air prevents dampness, rot, mold and mildew.
What kind of system is best for my boat?
There are many air conditioning products available on the market, but when determining which type of system to buy, the size of your yacht is very important. Utilizing the vast amount of water provided by the sea, most marine air conditioning systems use water cooling methods rather than air and this allows us to build a more compact unit to suit small on-board spaces. Self-contained systems are the best choice for smaller boats up to 40ft due to the lower cost and easy DIY installation, which is usually under a bunk or settee. Larger yachts up to 80ft should consider split-gas air conditioning systems, which have the condensing unit in the engine room and air handler in the living space. For larger boats and super yachts, chilled water systems are the ideal option and can be tailored to specific needs.
Which one should I get?
We all want to save a few bucks, especially at this time of year, but the cheapest option is not necessarily the best. Remember that buying an air conditioning system is not something that should happen often, so do your research. High-quality, innovative engineering is a must as is a manufacturer’s history in producing rugged systems that can withstand the harsh marine environments and work efficiently with the boat’s power source. Check out the brand’s reputation and whether it has a geographically broad service network– you never know when and where you might need it. For example, Dometic Marine has an extensive worldwide distributor and dealer network for its premium brands, to ensure that service and support are available anywhere in the world.
What maintenance is required?
When an air conditioning system has been installed and is working, the last thing a boat owner wants to worry about is carrying out endless maintenance checks. If the air conditioning unit is properly manufactured to a high standard, then only minimal maintenance will be required to ensure maximum performance and longevity of the system. Throughout the season the seawater strainer should be checked and emptied regularly to maintain good water flow, and the air filter should be cleaned or replaced periodically to maintain good air flow. For boat owners with self-contained systems, some DIY summer and winter preparation is recommended such as checking the thru hull and heat exchanger for any debris pulled in with the seawater as well as making certain the condensate pan is draining properly. Also check the system’s hoses, coils and other piping for leaks. In winter, you should run a little biodegradable antifreeze through the unit. Maintaining a split-gas system takes a little extra effort because the components are located in different parts of the boat, but the principles remain the same. In addition, check to ensure there are no refrigerant leaks between the components. A chilled water system will require regular service checks by on-board or local service engineers due to the complexity of the system.
What about electrical requirements?
The electrical consumption of air conditioning units depends on the size of the air conditioner but most run on alternating current (AC) power and come in different power configurations. Check out the specification sheets for the running current information for the unit and advice on how to select the right circuit breaker, but also make sure a generator, inverter or shore cord can handle the inrush current of the compressor when an air conditioner starts. Soft start technology reduces the in-rush of current caused by large compressor motor loads, therefore reducing and balancing the strain of the boat’s power source.
When we talk about a helm pump, we must also talk about both passive and power steering as that is the part of the system that interacts most with you and the rest of the steering system. Most passive (non-power assisted) systems are set up to be between 5 & 10 turns lock-to-lock on the steering wheel and if we translate into to mechanical advantage, it goes like this—We’ll use total rudder arc at 70 degrees (about 1/5th of a full circle and seems most typical in most steering installation guides) for this example– If it takes 7 full 360 degree turns of the steering wheel to give full stroke or full rudder travel, then you have about a 36:1 gear (actually hydraulic) ratio between the two.. All else being equal, most steering systems fall in the 20:1 to 40:1 ratio range. Think about it—you just went through 7 x 360 degrees of helm pump rotation (2520 total rotational degrees) , but the rudder only rotated 70 degrees of total arc; hence a 36:1 ratio, “on paper”(we’ll get to that later) between you (the steering wheel) and the rudder. Bet you never thought about it that way before!
Also need to mention that with passive steering you have both pressurized 3-line systems and non-pressurized 2-line systems. There are some that think
“pressurized” has something to do with power steering, but it does not. Hynautic (no longer as they were bought by Teleflex) invented the 3-line pressurized system for one reason—to make it simple to bleed and fill and to allow a less critical installation as to elevations of components, etc.. “Gravity” was not a concern with the pressurized systems. But with that, they added something that most don’t
know. It usually has a much higher steering effort because of an added complexity of more lines and valves. It comes down to internal friction that is created when pushing fluid through hose, pipes and fittings.
In a pressurized 3-line system, you typically have between 15 & 25 PSI at all times in the reservoir, “third line and the low pressure side of the pump. In a 2-line non- pressurized system (although you may still have a 3rd line), the reservoir and / or low pressure side on the system is at atmospheric pressure and relays on gravity and height to keep the flows right between multiple stations. That’s also why you can use clear vinyl tubing for supplying fluid between stations and or reservoirs.
The ram is really the key part or “foundation” of the steering system (in so many words, the “RAM” carries the load). The helm pump (at the other end) is just the fluid “pumper” and does not carry the load except while actually turning the rudder. Once the rudder is static, regardless of its actual position, the ram and steering lines (up to the check valves in the helm pump) are carrying the load, or pressures, developed in the system (the rudder is always being pushed, one way or another, from the vessel movement and / or water movement around or past it. Even a very small & inexpensive helm pump could turn a very big rudder on a large vessel quite easily, but this is not always a practical solution. As to selecting a RAM as to its base quality, to us this is a no-brainer. Brass, Bronze, and Stainless Steels alloys are the only acceptable materials that should be used for the construction of any RAM that even gets close to saltwater, or is used on any type of vessel larger than a run-about. Aluminum has no place in Hydraulic Steering RAM construction except (maybe) for fresh water use and super light duty applications.
The internal & external size of a ram is measured in a few ways—Common terms:
- BORE: The piston bore diameter—Inches or in millimeters—common sizes might be 1.25”, 1.5”, 1.75” and 2”
- STROKE: The total travel of the ram – 7” and 9” seem to be most common, but ram strokes come from about 5” to about 12”
- DISPLACEMENT: This is the mathematical computation of the bore and stroke measurements less the volume of the rod itself. This is the most important number as it tells you the relationship you will have with the helm pump as to how many turns the pump will have to make in order to move the ram a full stroke. An example—A 1.5” bore ram with a 7” stroke might have an internal displacement of 10 cubic inches; A typical helm pump may have an internal displacement of 2 cubic inches ( or 35 cc’s) per revolution.. This would mean that it takes approx. 5 complete turns of the helm pump to move the ram its 7” of travel. But in reality, always add about 10% to compute turns vs the real number you will end up with. Why (?) , because of internal hydraulic slippage that is always part of any hydraulic system that uses fluid to move something
Virtually all modern yacht engines are diesel engines however there are some other engines which are found on smaller yachts and high speed yachts (see gas engines, turbines at the bottom of the post).
All yacht engines have common requirements which will allow them to operate reliably for long periods:
1. Enough Air – Yacht engines require lots of fresh air for combustion. Engine compartments must be able to provide this even if it is forced in via fans. The ideal situation is to pull air into the engine room via the top deck, where the air is not as salty in ocean conditions, through fans that are variably controlled to provide positive pressure on demand, and with flaps that can shut off the supply of air in the event of fire.
2. Clean Fuel – With water and particulate matter filtered out. Most used yacht engines are equipped with pre filters such as Racor, to filter water and particles down to 10 microns before the engine filters which take it down to 2 microns. Another nifty product is the RCI purifier, which can take large amounts of contamination out of the fuel even before it hits the filters with cartridge elements. Fuel quality for yacht engines is more questionable the further yachts travel from populated areas, therefore it is imperative to have good fuel cleaning equipment on board.
3. Proper Loading – Yacht engines perform and operate best with correctly sized propellers which are kept clean. Engines must turn up to rated WOT (wide open throttle) and propellers should match this engine parameter closely. If not, there is a chance that the yacht engines will not load properly and have a life reduction.
4. Clean Oil – Yacht engines require oil and lubricants to be changed at regular intervals. Most modern yachts have built-in pumps with hoses and valves making this an easy task.
5. Efficient Cooling Systems – The cooling system and raw water pump must be serviced on a periodic basis. Note that new methods allow for descaling procedures without taking apart the units.
It is often argued that modern large diesel engines, especially with high horsepower ratings, are not designed to operate at slow speeds.
There is lots of debate among professionals in this regard. The common agreement is that engines of any type must be broken-in correctly when new or overhauled and that they should be run up to high speeds at least periodically every day of operation (to blow out soot).
It is a very good idea to have oil analyzed (even transmissions) every oil change, similar to a blood work-up – as one can often catch problems early before they get detrimental.
Yachts for sale which were built before 2000 would most likely find either Detroit Diesels (GM) or Caterpillar.
Detroit Diesel Yacht Engines
Detroit Diesel (GM’s) is a two-stroke diesel engine, which means that it completes its combustion and exhaust cycle in two strokes. The advent of clean emission mandates forced these engines into obsolescence.
Mechanically controlled and governed up until the mid-1990′s with the DDEC series, these yacht engines pioneered the electronic controls which are now commonly found on most modern diesel engines.
Most commonly found in yachts prior to 1998, the 6V71 (rated between 210 and 480 hp) and the 12V71 (various ratings between 550-900 hp) (the 1271 is two 671′s put together – 71 referring to the cubic inches per cylinder – either 6 or 12 cylinders) engines are the most common engines found in older US yachts today, along with their sister engines – 6V92,(550 hp) 8V92 (710 hp), 12V92 (1050 hp), and 16V92′s(1350 hp) (these engines eventually obtain the higher DDEC ratings via electronic controls).
These yacht engines were notorious for lots of low end torque and simple mechanics. Noted for shortened intervals between overhauls when operated (or loaded too hard) and run in hot conditions with not enough air. If an owner takes care to maintain and operate these popular yacht engines at slower speeds, they last quite a while.
Caterpillar Yacht Engines
Caterpillar – Noted prior to 2000 for the 3412 (a V12 engine commonly rated between 1000-1450 hp on used yachts) and the 3208 (rated between 375 -425 hp). The inline-6 series engines started coming out in the late 90′s with the 3116 (350 hp), 3126, (450 hp), the 3176-3196 (660 hp) and the 3406 (800 hp).
All of these early CAT 6 cylinder engines suffered from some issue or another. The point is that all yacht engine manufacturers have issues with engineering flaws. The important thing is how they take care of it – and CAT developed a good program to deal with this.
The newer models of these same engines – the C7, C9, C12, C18, C30, and C32 – all have been pretty reliable and are one of the two predominant engine manufacturers in today’s yachts. The CAT 3512 is the powerhouse for the larger yachts.
Modern emission requirements have brought the advent of the modern electronically controlled diesel and the high-pressure injection service used to more efficiently controlled fuel injection. Most engine manufacturers refer to this technology as ‘common rail’ while CAT refers to it as ‘acert’.
MTU Yacht Engines
MTU of Germany merged with Detroit Diesel in the late 90′s and developed a series of popular 4 stroke engines – the 8V2000, 12V2000, 16V2000, 12V4000 and the 16V4000 engines.
The Series 60 engine has also been a very popular model, long upheld in the trucking industry. Many of these yacht engines are found on today’s yachts and have held up quite well. Some of us wonder if their parts are made of precious metals due to the cost.
MAN Yacht Engines
MAN has been a popular German engine in used yachts – especially sport fishers, because of its superior horsepower to weight ratio and relatively compact size.
Yanmar Yacht Engines
Yanmar has been a very reliable Japanese engine, popular with sailing yachts, trawlers, sport fishers and some motor yachts. Their mechanical 500 hp engine has been superb. They have recently merged with a little known (but excellent) Scandinavian manufacturer Scania to build a larger series of electronically controlled engines.
Volvo Yacht Engines
Volvo engines have been a long-time supplier of used yacht engines. Most recognizable are the 480 hp engine (noted for smokiness) and the 700 hp D12. Volvo is pioneering the ‘pod’ technology for yachts, eliminating typical shaft driven/rudder systems.
These engines are designed with the whole engine, transmission, exhaust and propeller as one unit, thus saving lots of space (not to mention problems associated with traditional shaft systems).
These 660 hp units can be installed as 2 or more units next to each other that electronically turn as a synchronized system – or ‘fly by wire.’ The drives are designed to tear away without causing a hole in the hull in the event of grounding or hitting something hard.
Yacht Engines by Cummins
Cummins is also a big player in the yacht industry. Especially noted for high quality, reliable service, the Cummins 300-400 hp Diamond series and the QSM11 (660 hp) have been terrific engines.
Mercruiser and Cummins have partnered up to produce a pod diesel engine as well – known as the Zeus for multiple unit installations and rated at 715hp.
Diesel engines of lesser notoriety, but still found on yachts, are:
- Deutz (German)
- Perkins (British)
- Hino (Chinese)
- Ford Lehman (US)
- John Deere (US)
The average marine gasoline engine runs for 1,500 hours before needing a major overhaul. The average marine diesel engine will run for more than three times that long and log an average 5,000 hours under the same conditions. The number of hours that a marine engine runs is very dependent on the amount and quality of maintenance over the years.
The typical gasoline marine engine will run fine for the first 1,000 hours. It is at this juncture that the engine starts to exhibit small problems. If these small problems aren’t addressed, they can turn into major problems which may make the last 500 hours of life difficult to reach.
Interestingly, an automobile engine may run almost twice as long (3,000 hours) as your marine gasoline engine. The reason is that marine engines normally work harder and under worse conditions than automobile engines. A well-maintained gasoline engine run under the best conditions may well run for more than the 1,500 hours without major overhaul. However, many that operate under the most atrocious conditions of salt air, damp bilges, intermittent operation and pure neglect will certainly die early.
Diesel engines are built to finer tolerances than are gasoline engines. They will accept much more abuse and often deliver, if well maintained, 8,000 hours of hard work before need a major overhaul. Theoretically, a well-maintained diesel may last the life of your boat. Since the average recreational boater logs only about 200 hours per year, the 8,000 hour diesel would last 40 years.
Although diesels can add considerable cost to a boat, they should be seriously considered because of their durability, economy of operation and safety concerns. Diesel fuel has a much higher flash point than gasoline and does not present the same threat of explosion that gasoline fumes carry.
Engines like to run long and steady. The shorter the running time between stops, and the longer the idle time between runs the fewer the hours they will deliver before needing major repairs. The adverse conditions under which marine engines operate have a great deal to do with their longevity. What they really need is rarely what they get. Naval architects recommend that engine compartments should be supplied with lots of dry, cool (50 degrees F), clean air. The very minimum fresh air vent area (in square inches) for natural ventilation without blowers is found by dividing engine horsepower by 3.3.
Two of the most important rules of thumb for engine compartment blowers on gasoline engines are that they should always be set to exhaust, not to blow air in, and they should be run for a minimum of 5 minutes before starting the engine. Two indicators that can alert you to potential trouble are the color of exhaust smoke
and changes in the appearance of your oil when you check it.
Exhaust gases from marine engines should be clear.
Any color of smoke can warn you of potential trouble.
- Black smoke is the result of engine overload, a restricted air supply, or a malfunctioning fuel injector in the case of a diesel engine. Improperly burned particles of excess fuel are blown out the exhaust.
- Blue smoke is formed by combustion of the engine’s own lubricating oil. This can be the result of worn piston rings, valve guides, or oil seals. The oil can come from an overfilled air filter in the case of a diesel engine or excess oil in the crankcase.
- White smoke indicates either water vapor from dirty fuel, a water leak into the cylinder or atomized, but completely unburned, fuel. Air in the fuel can also cause white smoke.
You cannot check the level and condition of your oil in your engine too often.
You should check it at least once a day and preferably before every start. It is also a good idea to wipe the dip stick clean with your bare fingers and feel the consistency of the oil. Use the paper towel to wipe your fingers. You should rub the oil on the stick lightly between your thumb and index finger and feel for any foreign particles which could indicate contamination or metal parts failures. Weekend boaters checking the oil before starting should be suspicious of oil levels that are too high or too low.
- Too high a level might be a clue that water has found its way into the oil sump. You could crack the cylinder head; break a piston, or both, just by turning the engine over. The oil with water in it will also look “milky.”
- Too low a level could indicate an oil leak that could lead to engine seizure. Look in the bilge to see if there is any oil residue. Many marine engines sit very low in the bilge and water is consistently in contact with the oil pan. Over the years this can corrode and cause pinhole leaks in the pan.
Whenever there is a large deviation from normal, take that as an urgent warning. Start looking for more clues or seek the advice of an expert.
This boating season, and depending on how you handle it, fuel will either be a nagging problem or no problem at all. Here’s what you need to know, along with a few tips on keeping
your boat running strong all season long. It’s no secret alcohol-laced gasoline creates a boat load of problems including absorbing moisture out of the atmosphere. There’s also the fact that E-5 through E-85 gasoline shelf life is notoriously short. After about a month’s time the petrochemical begins to degrade into nasty gum and varnish that clogs up fuel injectors and carburetor passages.
Obviously it’s common sense to avoid alcohol altogether. Do that by scouting out marinas that sell unadulterated gasoline. Ask around. That said, it’s understandable that trailer boaters are tempted to pull up to a land-based gas station to top off with the less expensive road tax Regular gas. But whenever you use automotive fuel, be sure to dose the gasoline with marine-specific stabilizer before you start pumping. And no matter what the brand name of the stabilizer, before you even open the can, read the label and follow its instructions to the letter. Know that in general, the greater the concentration of stabilizer – the number of ounces added per gallon of gas – the longer the protection before it begins to sour.
It’s also important to know that alcohol fuel burned within three weeks, with or without stabilizer, tends to be problem free and for the same reasons your tow vehicle doesn’t have an issue with the stuff. The passage of time is the enemy of E-10 and E-15. Figure on a shelf life of about three to four weeks before the fuel rots and water seeps in. Meanwhile, back at the waterfront know that some fuel docks rather considerately treat their gasoline supplies with stabilizer (sometimes this means gas with alcohol – sometimes alcohol free) which means that when you top off dockside you don’t have to go to the trouble or expense of popping the top on your own chemicals.
No matter what the fuel source one must-have accessory item is a fuel/water separator, even on those portable outboard motors rated from 2 to 30 horsepower. Costs for a portable outboard motor sized fuel/water separator filter start at about $30 and replacement elements cost about $15. An element should last a whole season, or about 100 engine hours. Also good to know, on these miniature water/separator/filters, the filter element proper is a tightly woven 10 micron mesh that keeps tiny bits of gum (decomposing gasoline) and other particulate matter from clogging up a small outboard motor’s tiny main jet and passages. And because alcohol is corrosive, it’s pretty hard on all fuel system components. Likely as not the day will come when you squeeze the fuel primer bulb and watch in absolute horror as the contents of the bowl turn black in a swirling cloud of miniscule rubber particles. That the telltale sign that the primer bulb has rotted on the inside and may soon crack wide open and spill fuel. Imagine what would have happened if the rotten rubber had flowed to the fuel injectors or carburetor jets and you didn’t have the foresight to install a filter. You may also find little yellow flecks of yellow plastic which are the broken down remains of the fuel hose liner.
On larger boats with either gas or diesel engines it’s also a good idea to have a competent fuel cleansing system that begins at the fuel dock. Consider pre-filtering, or pumping fuel into a screened fuel filter jabbed into the fill tube. Its specially coated wide mesh screen not only keeps big junk out of the tank, but also separates out any free-standing water. The water drops down into a sump and is disposed of in an environmentally friendly manner. The first time you try one of these out you might be shocked at how filthy fuel can be. If your boat is diesel powered you probably already know about the fuel additives that kill microbes, the living breathing organisms that would otherwise thrive in diesel fuel. Kill them so they don’t proliferate and damage the fuel system. Once again, read the label and wear gloves to protect your skin.
Marine engines, as well as automotive engines are, cooled by circulating water thru the engine block. Marine engines are unique in that there are two different types of cooling systems. The standard raw water system and the fresh water cooling system.
Raw Water Cooling Systems
Raw water cooling systems draw water from outside the boat (seawater or lake water). Water is pumped from the source to the engine block then the engine circulation pump forces the raw water thru the engine block and the water is expelled thru the exhaust. Raw water cooling systems are relatively simple and the standard cooling system on most marine Engines. The raw water pump in most cases is inside the outdrive. On larger engines and inboard engines the raw water pump is located inside the boat and is driven by a v-belt or directly off of the crankshaft. There are hidden dangers that can accumulate over time causing you to spend big dollars on repairs. The danger is using salt water as a coolant in your engine. Salt water can be highly corrosive. Running salt water through your engine block and exhaust manifolds will lead to destructive corrosion that is unseen until your engine or exhaust manifolds fail.
Generally speaking, marine engines cooled with raw water, especially ones that use salt water, have a shorter life span than marine engines cooled with a closed cooling system.
Fresh Water Systems with Heat Exchangers and Keel Cooled systems
Fresh water cooling systems, also known as closed cooling systems come in several varieties. The most common type utilizes a Heat Exchanger which functions similarly to the radiator in your car. Coolant (antifreeze) is circulated through one side of the heat exchanger where it is cooled by raw water that passes through the other side of the heat exchanger. The engine coolant is then circulated back into the engine. The raw water is expelled out of the boat thru the exhaust. Another common type of closed cooling systems is known as a Keel Cooler. This is done by eliminating the use of a heat exchanger. Instead of pumping raw water into the vessel’s heat exchanger where it cools the coolant, the coolant is pumped through pipes or aluminum extrusions on the outside of the hull where the surrounding water (lake or ocean water) cools the coolant before it is pumped back into the engine. The use of keel coolers removes the need for a heat exchanger, raw water pump and the other components necessary for pumping raw water into the heat exchanger to.
Raw water refers to the water that the boat is floating in. It makes no difference whether it is salt or fresh; both are used to cool the engine. The process starts by drawing water into the engine through a seacock fitting and pumping it through the engine’s water jacket and ports by way of a mechanical water pump. In a raw water system the water is drawn up through the seacock by the water pump.
The water flows through the engine and directly out the exhaust. This cooler water absorbs heat from the engine to help keep it cool. Most new marine engines use an enclosed cooling system. This means that there is a small tank on the top of the engine that uses a combination of fresh water and coolant. This fresh water is circulated through the engine and through a heat exchanger. The fresh water, in this system, absorbs the heat of the engine. Raw water is still drawn up through the seacock but only flows through the heat exchanger jacket. This cooler raw water absorbs the heat from the fresh water through the heat exchanger jacket and is then pumped out the exhaust.
The advantages of the enclosed system over the raw water system are extreme, especially if you are operating in salt water. Salt water tends to build up a corrosive scale when the engine operates above 140°. In the raw water system this scale is building up inside the engine’s water jacket and ports. When the scaling builds to the point that water flow is restricted the engine starts to overheat. At this point you are probably looking at replacing the engine.
In the enclosed system, the water that flows through the engine’s water jacket and ports is the fresh water and coolant. The only part the raw water flows through is the heat exchanger. The same scaling occurs however. When water flow is restricted and the engine begins to overheat you may be able to “acid boil” the scale out of the heat exchanger and continue to use it. The worst case is that you would have to replace the heat exchanger. This would be much less expensive than replacing the engine.
Other components of the cooling system, whether it be raw water or enclosed, are the seacock, sea strainer, hoses and clamps, belts and water pump impeller. The seacock is a through-hull device that allows water to enter the hull from the outside. This device has a handle that allows you to shut off the water flow if you have a problem such as a loose hose clamp or cracked hose. You should test the seacock shut-offs monthly to make sure they are operable. As a backup safety measure you should have a soft, tapered, wooden plug (called a bung) of the size of the seacock tied to the seacock. In case a hose parts and you can’t operate the shut-off you can put the bung in the seacock to stop the water flow.
The next inline part of the engine cooling system is the sea strainer. This is a device through which the raw water flows and is designed to filter out debris, sand, leaves, etc. before it gets to the engine. This device works much like a swimming pool skimmer. There are several kinds of strainers but all have a removable filter or screen which should be checked and cleaned or replaced on a regular basis.
Hoses, clamps and belts are vital to the cooling system and should also be checked periodically. Every time you check the oil, which should be done before each start-up, you should visually inspect hoses, clamps and belts for wear. All hoses that are below the waterline should be double clamped. This will help prevent water from entering the bilge should one of the clamps fail. If you find a corroded clamp, a pinched or cracked hose or belt, they should be replaced immediately. Be sure to replace the hoses with the same size diameter, length and temperature requirements that the manufacturer suggests.
The raw water pump, which is driven by a belt on the engine, contains an impeller which makes the pump operate. It is usually fairly easy to access the impeller to inspect or replace it.
In the enclosed system, a commercial coolant (antifreeze) should be added. This will prevent the fresh water from freezing and damaging the engine in cold climates and also will help prevent corrosion build-up in the fresh water system. Normally you would use the coolant and fresh water in 50/50 mixture. In colder climates you may want to increase the coolant percentage.
In summary, the direct, raw water system circulates water through the engine water jacket which flows through the block, head, manifold, etc. This water absorbs the heat from the engine and is exhausted overboard. The enclosed system circulates fresh water and coolant through the engine water jacket and through a heat exchanger. This fresh water absorbs the heat of the engine. The raw water is also pumped through the heat exchanger where it absorbs some of the heat of the fresh water and is again exhausted overboard.
A propeller can be defined as follows: A mechanical device formed by two or more blades that spin around a shaft and produces a propelling force in boats (or airplanes). There are several technical terms to define the propeller’s characteristics such as: diameter, pitch, disc area relation, hub, bore etc. All these characteristics are calculated to design the optimal propeller accordingly to specific needs of the customer and the boat characteristics.
Pitch: Is the displacement a propeller makes in a complete spin of 360° degrees. This means that if we have a propeller of 40” pitch it will advance 40 inches for every complete spin as long as this is made in a solid surface; in a liquid environment, the propeller will obviously slide with less displacement.
The pitch concept is not exclusive for propellers; other mechanical devices like screws also use it. For instance, a screw with 10 mm of pitch will advance 10 mm for every complete turn when hit by the screwdriver. In fact, the “screw propeller” concept is literally making reference to that the propeller works exactly like a screw. It is very important that both, pitch and diameter are properly calculated. If for any given HP the pitch is too big, the propeller becomes heavy and demands more power than the engine can reach and vice versa, if the pitch is too small then we have a light propeller that wouldn’t absorb the engine’s full power.
So, what would be the appropriate pitch? Certain parameters need to be checked like power, rpms, gear reduction, size of vessel, vessel application (i.e. a trawler or a tugboat needs power while a yacht requires velocity).