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Piers and Lin du Pré are the owners of the Fleming 55 Play d'eau, based in Beaucette Marina, Guernsey in the Channel Islands at N49° 30’.197 W002° 30’.350.

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Descaling the heat exchanger

The Gulper pump connected to the tub of Rydlyme and the engine’s cooling system
click to enlarge

After 7 years, Play d’eau’s engine logs were showing an increase in water temperature of some 5 degrees on each engine when at cruise rpm.

The most likely cause was a gradual build up of limescale in the tubes of the heat exchanger. Certainly, when squeezing the rubber hoses of the cooling circuit, they ‘crackled’ as the limescale crumbled.

Being short of time, removing the heat exchangers and sending them away for cleaning was not an option. Furthermore, it would not resolve the limescale problems in the rest of the cooling circuit.

So, after research on the web, I devised an alternative solution. I would ‘descale’ the complete cooling circuit of each engine by circulating Rydlyme instead of sea water.

Normally, sea water is sucked through a strainer by the sea-water pump where the impellor forces it into the engine’s cooling circuit and heat exchanger before it’s finally dumped overboard. Some of this sea water is bled off to be sprayed into the engine’s hot exhaust gasses to cool them.

The OUT side of the Gulper connected to the start of the engine’s cooling circuit
click to enlarge

My plan was to use a Gulper pump in place of the sea-water pump and a large tub of the dark brown Rydlyme in place of sea water. A pipe would connect the tub to the IN side of the Gulper with another to connect the OUT to the hose at the start of the engine’s cooling circuit.

Not to lose the Rydlyme overboard, I connected a pipe from where the sea water would normally discharge overboard back to the Rydlyme tub. Making the hose connections required a number of hose connectors which were all readily available at the local Chandlery.

The final preparation required the removal of any anodes since these would be attacked by the Rydlyme. In their place, I used blanking plugs.

Testing involved turning the Gulper on and checking for leaks using water from a tub. None was found. Now for reality. With the water replaced by Rydlyme the Gulper was started and soon the dark brown liquid was fizzing away as all the limescale was being eaten away.

It took about an hour per engine before the fizzing and frothing stopped indicating no lime scale was left. Checking that it wasn’t just that the Rydlyme was spent was simple – I dropped a piece of limescale into the Rydlyme. It fizzed showing there was life in the dark brown.

The end of the engine’s cooling circuit connected to a pipe to return to the tub of Rydlyme
click to enlarge

Overall, the exercise took less than one day. Total success. Both engines had been fully descaled, the proof of which was a reduction in cruise water temperature to the original figure. Yes!

Piers
from the Engine Room of
Play d’eau
Fleming 55

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