Winter storage in the water: How to keep your mooring free of ice

More and more boat owners are deciding to leave their boats in the water over the winter. The reasons behind this, as well as the pros and cons, are certainly open to debate. One thing is clear, however: even in winter, a boat trip – or at least an evening of mulled wine with friends and acquaintances on board – can have its charms. And anyone who has ever spent New Year’s Eve on a boat would certainly not want to miss out on that experience again.

However, one thing is also clear: precautionary measures – for example, to prevent the boat from freezing whilst afloat – should be taken in all cases. Furthermore, you should protect the boat and your equipment from damp to make your time on board as comfortable as possible. In our Winter Journal, we provide tips on the following topics: mooring, heating, dehumidification, frost protection and monitoring.

Protection for the hull – how to keep your mooring free of ice

Submersible pumps or aeration systems prevent the boat from freezing in the water

There are essentially two tried-and-tested methods for keeping your mooring free of ice. The simplest option is to use one or two submersible pumps. When necessary, these pump the warmer deep-water from beneath the hull, thereby keeping it ice-free. Even when air temperatures are in the double-digit sub-zero range, the water in the deeper layers never cools below zero degrees. In winter, temperatures of between two and four degrees Celsius are common at a depth of two to three metres.

If this ‘warm’ water is then pumped to the surface, the higher temperature and the movement of the water’s surface ensure that the hull and its fittings do not freeze.

Photo guide: How to build your own pump system and what you’ll need

The function

Our ‘ice-free system’ operates in two stages and only switches the pumps on when there is an actual need. This behaviour is achieved, on the one hand, by a temperature switch and, on the other, by a timer connected in series.

In practice, a floating temperature sensor monitors the water temperature and transmits this reading to the temperature switch. If the temperature at the water’s surface drops below zero degrees, the timer is activated, which in turn runs the pumps at the previously selected interval. Depending on the timer used, it can be programmed in 10- or 15-minute intervals.

In practice, 15 minutes of pumping per hour is sufficient throughout the winter; on particularly bitterly cold days, 2 x 15 minutes per hour is recommended.

The minimum equipment required consists of a temperature switch with an external sensor, an outdoor timer and at least one submersible pump (see parts list).

Pumps

When selecting a pump, there are several factors to bear in mind: Firstly, the pump must be ‘suitable for use with contaminated water’. Otherwise, contaminants in the harbour water or accidental contact with the seabed can damage the impellers of submersible pumps and lead to failure. Secondly, the pump must have a sufficient immersion depth. Depending on the type of boat, an immersion depth of five metres should certainly be sufficient. The flow rate is directly related to the electrical power. To keep electricity costs under control, we opted for a 400-watt pump with a flow rate of 140 l/min. If necessary, this means that around two tonnes of ‘warm water’ are pumped from beneath the hull per operating cycle (15 minutes); experience shows that this is more than enough. Depending on the length of the boat, you should use several pumps. For small and medium-sized boats up to about eight metres in length, one pump is sufficient; for longer boats, you should use two, or even three for very large boats, which are then distributed along the hull according to the boat’s length.

Pump installation

The key to a properly functioning ice-free system is the correct positioning of the pumps. As a submersible pump generates torque when it starts up – which is further amplified by the flow of water during operation – suitable measures must be taken to prevent it from rotating about its own axis. The best way to do this is with a cross-brace approximately 1.5 m long, with a securing line attached to each end – on the starboard and port sides – leading to the railing (see diagram).

In our case, we used an aluminium angle profile, to the centre of which we secured the pump using several sturdy cable ties. It is important that the pump outlet faces upwards rather than to the side. It is also important to ensure that the lines attached at both ends are always the same length, so that the cross-brace and the pump hang horizontally beneath the boat. This can be achieved by applying coloured markings to the lines (paint). The lines are then secured to the railing or cleats. If only one pump is used, it should be positioned approximately amidships. If two pumps are used, the rear one should be positioned beneath the engine compartment and the front one approximately one-third of the boat’s length from the bow. How deep the pump hangs beneath the boat depends, amongst other things, on the water depth. In practice, depths of around 1.5 to 2 metres below the keel have proved effective.

Timer and temperature monitor

In winter, the pumps are switched on and off by the timer, which in turn is powered by the temperature switch. To put it simply: the 230-volt shore power supply first goes to the temperature switch and from there to the timer.

As both devices are fitted with standard 230-volt Schuko sockets, they can simply be plugged into one another. Important: The switching capacity of both components must be at least equal to the maximum pump power. For our 400-watt pump, the thermostat and timer would therefore need to be rated for at least 500 watts. To cope with the pump’s higher inrush current, it is best to look for 16-amp models when purchasing; this will ensure you are on the safe side in any case. The temperature switch must always be fitted with a waterproof external sensor.

To protect all the electrical equipment from the effects of winter weather, we fitted the switches and sockets into a suitable plastic box on deck. If the cables are long enough, the box can also be placed in the cockpit or at the helm. Depending on the temperature switch, the switch-on and switch-off temperatures can be set as required. With our H-Tronic temperature controller, we set the switch-on temperature (heating) to zero degrees and the switch-off temperature to four degrees. To get the system up and running, all you need to do is connect the individual components as described and connect the temperature switch to the shore power supply.

Carbonation system

The second option, which is also popular with entire clubs or marinas during the winter, is what are known as air-bubble systems. These can be installed locally for individual berths or for entire harbour facilities.

Explained in photos: How rising air bubbles bat the sparkling water machine encourage physical activity

The pipes

Firstly, you need to determine the length of the pipework required. To do this, calculate the boat’s perimeter, i.e. twice the boat’s length plus twice its width. It is important to use the maximum values in each case to ensure there is sufficient clearance during assembly. Based on the length of the pipes, the number of holes and their diameter, you can now calculate the required compressor capacity. Experience shows that 1-millimetre holes spaced approximately one metre apart are sufficient to prevent the water surface from freezing over.

Once the length of the pipework has been determined, you can buy 1-inch plastic pipes, the necessary connectors and elbows, as well as a T-joint for the compressor connection, from a DIY store. Now assemble the pipework on land. Make sure that it remains detachable in a few places to make it easier to transport and install later. It is also important that the T-piece for the compressor connection is located roughly in the rear third of the pipework (depending on the planned location of the compressor). Joints that do not need to be undone again can be secured with plastic adhesive.

The next step is to drill the 1-millimetre holes. These are drilled into the top of the pipe, approximately one metre apart.

The fastening

The system is now attached to the boat. The easiest way to do this is with ropes secured to the railing or handrails. Care must be taken to ensure that the pipes hang about half a metre below the water’s surface. To connect the pipe system to the compressor, use a hose, which is attached to the T-piece using stainless steel clamps.

Compressor

As the compressor does not need to run continuously in winter, depending on the outside temperature (15-minute intervals are sufficient), it makes sense to control it using a 230-volt timer switch. You can also buy such timers at DIY stores, but you must ensure that the timer is suitable for the compressor’s high inrush currents. Depending on the compressor, these can be up to three times the specified rated current.

The decision on where to position the compressor must be based on the layout of the boat. However, a location in the cockpit is usually sheltered from the weather and offers the shortest connection to the pipework.

How to calculate the compressor

Pipe length in metres / borehole spacing in metres multiplied by 0.7 m³/h gives the compressor capacity in m³/h.

• Example of a 10-metre boat: 27 m / 1 m × 0.7 m³/h = 18.9 m³/h

The compressor should therefore have a capacity of around 20 m³/h. This rule of thumb applies to 1-millimetre boreholes, a pipe burial depth of around half a metre and a compressor pressure of 1 bar.