You want to have the water comfort you know from home on your boat too. That means in particular: When I turn on the tap, I want water to flow evenly. On smaller boats in particular, there are still some mechanical foot pumps or the electric version with a switch contact on the tap. The disadvantage of both systems is that you can only use one tap at a time. The stern shower on the bathing platform, shower in the wet room, washbasin plus sink cannot be operated with this system.
The solution when there are several taps on board: the so-called pressurised water pump, which, like a domestic waterworks, always maintains a certain pressure, ensures the necessary flow at all taps and, above all, switches off again automatically when not in use. Domestic technology shows the way: If you have a garden at home, you may also have a small domestic waterworks for irrigation. This is a pump with a pressurised tank. Water is stored in the tank and kept at a pressure of around 5 bar. When you turn on the tap, water flows out and the pressure decreases. However, before it reaches zero and the water flow stops, the pump switches on and pumps fresh water from the well. The automatic pumps on board don't have it quite so difficult; they "only" have to draw the water from the water tank, which is usually located in the bilge. Another difference: the on-board pumps often do not have a pressure equalisation tank as standard. However, this vessel can be ordered as an accessory and ensures a smoother, more even flow of water in the pipes. The disadvantage of these pressurised reservoirs? Hygiene: A tank is a breeding ground for germs, as the flow rate in the tank is noticeably lower than in the pipes.
The test candidates
We ordered eight mid-range on-board pumps without pressure equalisation tanks and tested their performance. We purchased from the accessory retailers AWN, Gründl and SVB as well as from the online-only retailer Amazon. The latter supplied the rather unknown brands Seaflo and TTulpe, while the other candidates came from Flojet, Jabsco, Johnson (two units), Shurflo and Whale.
All pumps are multi-chamber diaphragm pumps and are driven by 12 V electric motors. The same pumping principle - but with only one diaphragm - is also found in a commercially available manual drainage pump. The diaphragm is moved back and forth with the pump rod, which draws in water in one direction and pushes it out in the other.
Back to the drinking water pumps: According to the manufacturer, they have a flow rate of between around 10 and 13 litres/min. This is sufficient for a boat with a shower and taps at the washbasin and sink. The online search engine gives the water consumption for a normal shower in the house as 12 l/min, but shower heads with an economy function (around 6 l/min) are also recommended. The latter is of course particularly advantageous on board, as we can only use the amount of water that fits into the usually very limited fresh water tank.
Test setup
In our test set-up, we orientated ourselves on practical experience: The pumps are often not positioned directly at the level of the tank, but slightly higher. During our test run, the pumps were positioned around 0.50 m above the tank - which requires self-priming. A discipline that all pumps fulfil, but the TTulpe only did so after we removed the pre-filter, as this drew in air, which of course made it difficult for the pump to draw in water. The pump then ran perfectly without the filter.
As the taps are often not at the same height as the pumps, we let the hose run down again in a slight curve and then ran it back up about 1.70 metres (almost shower head height). In other words, all under difficult conditions with a total height difference of around 2 metres from the intake basin and back. The test candidates were connected using the hose connection often found on boats. We operated the 12 V pumps via a battery powered by an adjustable charger. This enabled us to provide all pumps with exactly 12.3 V. We fitted a T-piece to the outlet side of the pumps, with a pressure gauge connected to one outlet and a digital flow meter installed on the other, with a stopcock behind it to regulate the water flow. When measuring the flow, we set this tap to full flow and did not connect a reducer such as a shower head or similar to the end of the hose.
The results
In terms of flow rate, all pumps on our BOOTE practical test bench are below the manufacturer's specifications. The Johnson WPS 3.5 shows the highest value at 10.2 l/min and the Shurflo Aquaking II the lowest at 9.2 l/min. But even with this quantity it is still possible to shower.
The cut-off pressure of the test candidates is specified by the pump manufacturers as 1.7 to 3.4 bar. The higher the water pressure, the more certain it is that there will be enough water at the end of long pipes and hoses with many 90-degree angles. Around 2 bar is required for normal operation. In the pressure measurement, the Johnson Aquajet 2.9 shows its true size with a shut-off pressure of 3.4 bar, with three test candidates in the lower places at 2 bar: Jabsco Par Max 3/12V, Shurflo Aquaking II and the Seaflo pressurised water pump. The switch-on pressure is just as important, because without this point the pump does not "know" when it should start again. If the difference between switching on and off is small, it can happen that the water jet pulsates due to the constant switching on and off of the pump when a small amount of water is withdrawn. Here the Shurflo shows the smallest difference of around 0.3 bar, followed by the TTulpeflow at 0.5 bar. The greatest pressure difference is found with the Johnson WPS 2.9 at 1.4 bar. However, high pressure also means that there is a higher load on the pipes and therefore also on the screw fittings and connections. So, regardless of how much pressure a pump generates, here's a tip: if I'm going to be off the boat for a long time, the pump should be de-energised so that the entire fresh water tank isn't pumped empty and the pump then runs dry in the event of a line fault. This not only results in a mess in the bilge, but also causes extra wear on the pump and increased heat generation. We ran our test candidates for 10 minutes without water, which resulted in a temperature increase of less than 10 °C compared to the temperature during the test run. The degree values on the housings of the motors were between 12.9 °C (Flojet) and 16.6 °C (TTulpe) at an ambient air temperature of a good 10 °C. This means no problem for all pumps in this climate. The only thing that stood out was that the TTulpe became louder after a short drying time; the measuring device showed 71 dB/A at a distance of 1 metre.
On-board comfort naturally includes the background noise, and nothing is more annoying at night or at a quiet anchorage than a monotonous noise from the storage box, which is possibly amplified by loose shelves. An encapsulated installation location is important here and that the attachment points are decoupled via rubber buffers - a point that all test candidates fulfil. In test operation, Aquaking II from Shurflo was the quietest at 51.6 dB/A. The two pumps from Johnson stood out in this discipline with a "rich" sound. They were the loudest with values of around 60 dB/A, although the noise was not really unpleasant in test operation.
We measured the highest current consumption (between 6.3 A and 7.9 A) for both Johnson pumps, followed by the Whale pump. However, these values do not play a particularly important role for the on-board battery, as the tank is usually empty rather than the on-board battery. Example: With a duty cycle of 30 minutes, the Johnson WPS 3.5 with 3.8 A (in test mode) draws 1.8 Ah from the battery and 306 litres of water from the tank. The focus is therefore more on the appropriate cable cross-section and fuse protection. The latter can usually be found in the operating instructions or on the rating plate.
Pump selection
If the drinking water pump has given up the ghost - whether due to frost damage or old age - the easiest thing to do is to use the old pump as a guide. However, if you were not satisfied with its performance, we recommend the next larger pump.
No pump with a particularly low or high flow rate stood out in our test. If you are looking for pressure performance, i.e. long pipe runs, the two Johnson pumps from Whale and TTulpe are a good choice. When it comes to noise, Flojet, Jabsco, Shurflo and TTulpe are at the lower end of the scale. As far as the service life of the pumps is concerned, we are unable to make any objective statements as we were unable to carry out an endurance test. Good maintenance is important for the service life of any pump - especially before winter.
Ralf Marquard
Deputy Editor in Chief BOOTE
