8 low-cost bilge pumps compared


A discharge pipe held aloft tested the pumps’ maximum head of water


Current draw was measured to help work out the pumps’ overall effi ciency Finally we let the pumps run dry


uses a Whale Gulper displacement pump and a separate strainer. For our fi rst test, we connected


Flow rate was measured through a 5m pipe and skin fi tting at 1m head INSET The higher fl ow rates hit the back of our test tank with some force!


How we tested them


The pumps were screwed to a wooden base which was then held down with weights inside a large plastic box fi lled with water. Power was supplied by a variable voltage DC source. For the standard test we used 12V, but we also investigated the performance at


13.6V – which is available when the engine is running – to see how it might improve their performance. All the low-priced pumps tested


were of the centrifugal type, but by way of comparison we also looked at a Whale Automated Remote Mounted Bilge Kit, which


the pump to a long discharge pipe held up towards the laboratory ceiling. We were then able to measure the total head the pump was able to support. Next the pumps were attached to


a 5m length of 19mm diameter (3


⁄4 in) discharge pipe with a


standard skin fi tting on the end, and the time taken to pump 10lt through a height of 1m measured. This enabled a fl ow rate to be calculated in litres per minute. We also pumped the water through a non-return valve to see how much the valve affected the fl ow rate.


to measure the depth of water left in our ‘bilge’.


Centrifugal pumps


 Are not self-priming – they have to be fl ooded to function


 Will operate dry for a short period without harm


 Will operate against a closed discharge outlet


 Will allow small-sized solid matter to pass through


 Are very sensitive to head pressure and can stall easily


Choosing and installing electric bilge pumps


Though the number of brands on the market has reduced slightly since our last test (PBO May 2008), most manufacturers offer a range of models to suit different boat applications. They come in 12V or 24V, manual or automatic versions. For manual pumps, an external automatic switch such as a fl oat switch can be fi tted to operate the pump when the bilge water reaches a preset level. ISO 15083 gives the following


minimum performance requirements at 1m head, which are a useful guideline as to which pump to install:


Boat length


Less than or equal to 6m


Longer than 6m, less than 12m


Minimum fl ow 10 litres/min 15 litres/min Longer than 12m 30 litres/min


Installation Manufacturers’ advice on how to install a bilge pump is consistent: the pump should be located in the lowest accessible part of the bilge. Remember that you must be


able to access the release mechanism to dismantle the


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


pump for cleaning or unblocking. For sailing boats it should be centred over the keel. The pump should be mounted


on a marine plywood pad that is glassfi bred to the hull. The discharge pipe must rise


upwards with no dip and, ideally, be as short as possible. Avoid sharp bends and ensure the discharge is at least 300mm above the water line. For sailing boats the preferred discharge is, like the engine exhaust, at the stern. If it has to be straight over the side, an inline non-return (check) valve can be


fi tted to prevent backfi lling, but this will lower the fl ow rate. All the pumps, except the Whale Supersub, have ‘barbed’ discharge connectors which, because the end is tapered, are easier to connect up to the pipe. However, they can be diffi cult to remove. Warming gently with a hot air gun or soaking in hot water facilitates assembly or removal. Electrical wiring connections


should be made well above bilge water levels, and a correct size fuse fi tted to prevent the motor burning out if debris should happen to jam the impeller.


53


 Bilge_fjp.indd 53 05/07/2012 10:08


Page 1  |  Page 2  |  Page 3  |  Page 4