Bilge pumps, the unsung hero of your boat.

Ever heard the saying "not all heroes wear capes?", the bilge pumps on your boat are the real heroes, tirelessly ensuring the boat stays afloat, often installed hidden out of site and forgotten, they are there for your safety, they are also one of the most misunderstood pieces of essential hardware, lead the hardest life and too often are neglected.

Normal bilge pump function

The bilge is the bottom of the bottom when viewed from the inside, so if you are in the engine room on a large boat and you look at what's below you, you are looking at the bilge, usually its the lowest part of the boat where water would accumulate.

A bilge pump is an electrical, mechanical or manual pump that sucks water (and oil, detritus, hair, spanners, old screws) out of the bilge and deposits it overboard.

An amount of water in the bilge during normal boat use is normal (despite what people might tell you), this water comes from various sources, including washing the boat, where the deck drains into the bilge, the shaft packing glands, rain water ingress, engine room condensation during the combustion process of the engine(s) getting hot and then cooling down. This is where your bilge pump(s), work normally, the water level reaches a certain point, a float switch or other type of automatic switch then activates the pump, the water is pumped  overboard until the normal level has been reached again, the pump then stops, coming back on when activated by the automatic switch or manual activation via a dashboard or control panel mounted remote switch or button.

Emergency bilge pump function

The second use (but really its primary function) of the bilge pump is during an emergency, when there is large water ingress into the boat, be it from an accident, heavy weather or machinery failure, some examples;

Heavy weather, large waves and/or torrential rain causes a lot of water to enter and the pumps work to maintain the boat afloat.

Accident, the hull is breached, for example a porthole blows in, striking a floating or partly submerged object or unforeseen circumstances cause the vessel to take on a lot of water.

Machinery failure, rubber exhaust hose fails and pours salt water into the bilge, outdrive rubber bellows tear and allow seawater to enter, major shaft stuffing gland failure lets sea water in, or as I have seen once, a rudder came clean off, leaving a two inch wide hole in the bottom of the boat (this is very rare).

Bilge pumps play a critical role on the boat, that's why it makes no sense to me when I see the way they are installed by the boat builders or boat owners, or,  when someone would spend a fortune on a stereo, but tell them they need a new bilge pump and they give you a look like they're going to cry.

Types of pump

Centrifugal pump, the most common, the major brands include Rule, Attwood and Johnson, the motor in the body of the pump spins an impeller which sucks water up and pushes it through the outlet hose to an overboard fitting, the pumps are available in 12V, 24V or 32V. They can have an integrated float switch or they could be activated by an exterior one, they should have a permanent electrical supply, so when the batteries are switched off, the pump will still work for when you are not on board.

Centrifugal bilge pump, float switch and anti return valve

Centrifugal pumps are rated by how many gallons or liters per hour they can bail, you should take these figures with a pinch of salt, the ratings are for how much water they can discharge horizontally with a perfect electrical supply, if they have to push this water upwards (called static head height) their capacity and ability to bail is hugely reduced, by as much as fifty percent!

The number of problems I see that are blamed on the bilge pump is huge, but in reality it is not the pumps fault, an example, in Southern Spain when the rain comes, they get other countries yearly rainfall in a week! The bilge pump(s) work, bailing away keeping your boat afloat, now the batteries run low, because they are poorly maintained, because the shore power cable connected to the dock has its power cut because of the bad weather (this happens a fair bit), the pump installation is marginal, some dirt in the bilge blocks the pump, the pump blows its fuse, there are any number of reasons for failure, now the pump doesn’t work as well or possibly not at all, it cannot keep up with the demand, the result is the boat sinks in its mooring (boats sink a lot more often in the marina than out at sea), or, the boat partly sinks in its mooring and a lot of damage is done.

"It was that way when I got the boat"
This is no excuse, you should consider checking the bilge pump(s) as part of routine maintenance, check the fuse and the electrical connections and the float switch, at the first signs of deterioration, rectify it before it becomes a problem.

This video is well worth watching, an updated comparison of mostly centrifugal bilge pumps, I was quite surprised at the results.

Building a better mousetrap

There are alternative types of bilge pumps to the common centrifugal type, apologies in advance for lack of photos, for such a common item on a boat, bilge pump photos are surprisingly thin in number, I will update this article with photos when I have them. If you are interested, all of these types are very easily found online.

Diaphragm pumps, these pumps have a motor that operates a rubber (or sometimes more resilient material) diaphragm that works in a similar way to bellows for an open fire or a musical instrument. They must nearly always be installed with a particulate filter on the inlet to avoid damaging the diaphragm.

These types of pumps are not suited as the primary bilge pump as they generally have a lower rated pumping capacity, but, they work well in areas that would be difficult to remove water from and can be mounted in an area convenient for service as the suction end of the inlet hose can be a good distance from the pump. They sometimes get used for draining shower drains or grey water tanks. Whale is a major brand in this type of pump.

Advantages

• Self priming (the will expel any air in the outlet and outlet hoses)

• The can push past a lot of static head (the distance from the pump to where the bilge water is expelled overboard)

• Can run dry (long periods of running with no water without damaging the diaphragm or the motor)

• Rebuild kits and replacement motors available.

• Can pump the bilges almost dry.

Disadvantages

The flow rate is considerably lower than that of a centrifugal pump, a small pump might only be rated for 15 to 20 liters per minute.

Impeller pumps, sharing some similarities with diaphragm pumps but are considerably more heavy duty. These same types of pump get used for ballast tanks, diesel and oil transfer (not gasoline or similar thin fuels) and deck washing duties. The bigger units have superior flow rates to diaphragm pumps. This is where I would spend my money when improving a bilge pumping system.

Impeller share most of the same advantages and disadvantages of diaphragm pumps but there are some things to note;

• They are heavy, some of the larger ones are 8 kilos and more.

• They draw even more electrical current than diaphragm pumps or centrifugal pumps.

• The larger ones have superior flow rates, some are 50 liters per minute, but still way below a centrifugal pump, but will push that same flow rate up a considerable static head.

• Pricey, they are expensive, this is offset by being able to rebuild and service them.

• The do put up with an amount of debris going through them, this means no filter before the pump is always necessary.

Mechanical pumps, extremely robust, they are driven from the engine crankshaft pulley with a belt and can be engaged manually or electrically, sometimes referred to as crash pumps or clutch pumps. They are expensive to buy and require a bit of work to fit, possibly even requiring a crankshaft pulley with an extra sheave (groove) in it to attach the belt that drives the pump or a custom pulley to be made,  some diesel engines already have spare sheaves on the crankshaft pulley for attaching belt driven accessories.

When you are looking to buy one, the amount of water they say they move is actually the flow rate at a given rpm. Small ones might pump 80 liters per minute, big ones 200 liters per minute.

Because of the cost and installation needed for this type of pump they are not common on recreational boats, commercial vessels have used them for a long time. They are not suitable for pumping highly volatile liquids like gasoline. Some of the pumps use very large thru hull fittings for discharge, up to 2 inches (50mm) to ensure an unrestricted flow.

Engines, although not technically a pump, if you have the type of engine installation that has a sea cock and strainer to supply the engine with cooling water, a “T” valve can be installed. This type of installation requires a bit of work to operate but is a quite common installation on a number of larger recreational boats.

I know of one instance where someone had to use this exact setup, an exhaust hose blew off due to the clamps coming loose, this particular boat was 68 feet long and powered by two 1000 horsepower diesel engines, the captain saw fairly quickly what had happened and without missing a beat used one of the engines to drain the water (both engines were equipped with the valves for use as bilge pumps), you can imagine that a large diesel motor like that moves quite a lot of water.

Manual Pumps, as their name implies, they are of manual operation, rubber diaphragm type, the best are the double diaphragm ones, they pump when pushing the pump handle in both directions, i.e. in and out or up and down. They are only for use as a back up and some regulations call for having a manual pump installed.

Manual bilge pump filter box screwed into place in the bilge

One thing worth noting, this pump is powered by you and will only keep working whilst you keep pumping which, in summer can be quite hard work, if you accept this then a surprisingly large amount of water can be shifted, if your boat has watertight bulkheads, you may find two manual pumps installed, one for the engine room and an amidships compartment, or a valve to switch between the two, where they are very useful is for pumping the last of the water from the bilge, an electric centrifugal pump will always leave an amount of water, depending on the size and shape of the bilge this could be a little or it could be a lot, also the manual pumps use the diaphragm as an anti return or they have anti return valves incorporated in them, so once pumped water goes past the valve, it cant fall back into the bilge.

Room for improvement

Some boat manufacturers who shall remain nameless, install one small pump in an almost inaccessible place, how they can sleep at night beats me, one model I have seen, cost new €350,000 and had only one bilge pump between the engines, I have no idea how you could reach the float switch without doubling yourself over, there isn’t a snowflakes chance in hell that the pump could handle large water ingress but it meets minimum standards so that´s how it was installed.

Then there are some manufacturers who deserve a shout out for some excellent installations, these are Frauscher of Austria, Carver and Formula of the USA.

The Frauscher installation I saw had one large centrifugal pump plus two diaphragm pumps on a 30 footer! The diaphragm pumps were easily accessible, the centrifugal pump was also easy to reach once the engine room storage box was out the way.

Carver had used their know how, there is a section of the bilge that had a deep well, so they installed a custom built support for the pump and float switch that could be unclipped from the top of the well and the whole thing bought up for service, very good thinking.

Formula installed two large centrifugal pumps in a purpose built well (so all the bilge water would flow right into the well) at the front of the engine room, the pumps and float switches were readily accessible and not installed right between the motors and the engine hatch ram where you need to be a contortionist from the Circe de Solei to reach them.

Upgrading your bilge pumping system

Check your existing system first

Does the overboard discharge exit nice and high above the water line, if not, does the discharge hose from the pump have an anti siphoning bend?, that is the tube where it is connected to the bilge pump have a bend upwards from the through hull fitting to prevent water entering via the discharge hose, if it doesn’t, buy a longer length of hose and fit it. Check the hose connection to the through hull, make sure that it has a hose clamp, do not fit anti return valves in the discharge hose of electric bilge pumps, they cause more problems than they are worth (in my opinion), they get blocked and are another maintenance item, also it is more connections in the discharge hose.

The thru hull connection, or more specifically the fitting itself, the can be metallic or plastic, I would recommend inspecting them very closely, especially the plastic ones, over time the plastic gets deteriorated by the sun, the can crack and leak, I have even seen them sheer clean off, the discharge hose then falls back into the bilge area, so no water goes overboard. I would always recommend replacing with bronze, brass (okay above the waterline) or stainless steel. This inspection is particularly important if you have the thru hull discharge close to the waterline.

Fit a second pump, this is best done when the boat is out of the water as you will have to fit a through hull fitting for discharge, make sure you correctly install the pump with quality electrical terminals, proper marine grade stuff, not automotive ones, keep the wires off the bilge floor, make the connections permanently live, when you install the float switch, make sure in all cases that the float switch is higher than the bilge pump (for external float switches) or else the water level will fall and the pump will keep working and not pumping any water overboard.

This second pump can be considered for emergency use when the principal pump cannot keep up with the demand, fit a high water bilge alarm, so when the second pump starts working an alarm will sound to notify of the high water level in the bilge, size the pump the same as the first or an alternative is to fit a larger second pump, this is fine but remember that pumps are only as good as the batteries that are powering them.

Minimizing the need for bilge pumps

This will range from boat to boat but some good starting points;

Deck drains, see where they drain to, this is a good idea anyway, check especially for areas where the deck drains allow water to drip straight onto machinery or electrical installations (surprisingly too often).

Grey water, this is water from sinks and showers, on some vessels (usually much older ones), the discharge from basins and showers goes straight into the bilge, fit a shower box or grey water tank, this is a box with entries from the sink and shower discharges, it has an exit that needs to be connected in the same way as a bilge pump to a though hull fitting and its own bilge pump fitted in the box.

Air conditioning drains, these are often overlooked, if you have air con, the compressors create water from condensation, this water drips into a tray and then straight into the bilge, I have seen some that stain carpets and turn anything stored in bilge lockers moldy, so connect the drain to the same shower box.

Batteries, do not skimp on batteries, buy quality heavy duty batteries for your boat (an article on batteries will be coming in the future), they will pay for themselves in the long run, a better quality battery will keep your pumps pumping better for longer.

Bilge pride, keep your bilges clean, bilge pumps will put up with a certain amount of debris and dirt, some better than others, but ultimately sludge, hair, mud etc. will shorten their life dramatically, trust me when I say you will never find out at a convenient point, when you are still in your berth or the boat is in dry storage and you have all the time in the world to deal with it.

Twin centrifugal pumps, this bilge is filthy but the pumps still worked

If you have got this far, I want to say a big thank you for reading the (long) article. I cannot stress enough how important bilge pumps are, nor I can I say how often I have and still do see such marginal installations and how it should not be so.

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