Gear test


Submersible electric bilge pumps


Measuring fl ow rates and current consumption, Alex Bell and a PBO test team pump out the volume to fi nd which low-cost electric bilge pump performs best


rated to pump 500 gallons per hour (gph), which is around 37 litres per minute. These are


A


typically used in boats up to 30ft (9m) in length.


We set out to test 500gph, 12V manually switched submersible pumps at the lower end of the price spectrum. Six manufacturers supplied eight pumps to suit these criteria.


Manufacturers commonly rate pumps at zero head and at a head of 1m, although other criteria are sometimed used. ‘Head’ refers to the height to which the pump has to raise the water: the higher the head, the greater the work the pump has to do, which then reduces the fl ow rate.


Besides the pump having to


overcome gravity, fl ow is also restricted by the friction in the discharge pipe and by tight bends, non-return valves and the skin fi tting at the outlet. Previous tests I’ve done suggest that these losses could actually be greater than those incurred in lifting the water, so the shorter the pipe used to deliver the water overboard, the greater the fl ow rate. There are two particular


situations when an electric bilge pump can earn its keep:


 On a mooring, when ingress from any small leaks can accumulate and create the risk of sinking. An electric pump, triggered automatically by


THE PBO TEST TEAM


Ex-Merchant Navy offi cer Alex Bell sails a Bénéteau First 305 and lectures in maths and engineering at


Southampton Solent University. 52


Oksana Razina works at Southampton Solent University and has recently taken up club racing in the


Solent as navigator.


Chris Savage is currently undertaking the fi rst year of a four-year Yacht Powercraft Design Course


at Southampton Solent University.


rising water, can save the day, providing there is enough power in the battery.


 Another typical scenario would be in heavy seas, when the boat is ‘taking it green’ on the deck. With sailing boats this can be exacerbated by extreme heeling, which can bring water into the boat by all sorts of entry points. Occasional splashes or large drips are easily coped with by an electric pump, providing the suction point is underwater – but that’s not always the case when the boat is heeled. Manufacturers quite categorically


state in their installation instructions that their pumps are ‘not intended


to prevent rapid accumulation of onboard water due to rough


weather, hull damage and/or other unsafe navigational conditions.’ This is not a cop-out, they are being realistic: the pump would not be able to compete with a hole


Many pumps are installed with


switches designed to operate the pump automatically when the bilge water reaches a certain height. These switches can be of the fl oat type, which operate with mercury or a ball bearing making the contact. Newer designs require no moving parts and utilise a magnetic fi eld, but they require a


constant small current to operate this current. Yet another design starts the pump at regular intervals: if they detect resistance, they pump until the resistance ceases.


in the hull at the same depth as the What we were pump and the same diameter as the discharge pipe.


looking for The basic requirements for an effective bilge pump are:  That it fi ts the available space and delivers the bilge water overboard with minimum electric current consumption.  It shouldn’t block easily – and if it does, it should be easy to take apart and clear.  It must be durable and able to resist long-term ingress of water. Strangely, manufacturers don’t


specify a waterproof standard for their pumps. One manufacturer stated that the pump will operate up to a 2m depth and quoted IP65, but others caution not to leave them submerged – they’re not suitable for garden pond fountains!


Practical Boat Owner 551 August 2012 • www.pbo.co.uk Shurfl o 500


ccording to my local chandler, the most popular size of submersible electric bilge pump sold is


Johnson L550


Attwood Tsunami T500


ECS 500 GPH Whale Orca 500 Rule 500 GPH TMC 500 GPH Whale Supersub 500


TESTED


Bilge_fjp.indd 52


05/07/2012 10:06


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