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© 2019 by UK Marine Electronics Ltd

Winterise your Electrics

Get next season off to a flying start by Winterising your Electrics. Book an electrical health check.

A Guide to Winterising Boat Electrics

It’s that time of year again, the nights are drawing in and thoughts turn to evenings by the fire, mulled wine and Christmas trees.  Over the winter your boat must fend for itself in cold damp conditions without the care and attention it gets during the summer, so why not give your boat a little Christmas cheer before you head off for the winter?

The winter can be tough time for the boats electrical system, the damp is the worst enemy for the wiring, whilst the cold can adversely affect the batteries. Whilst modern electronics are designed to cope with this environment, a lot of the internal wiring can suffer, especially if left switched on.

This guide will help you to make sure that come the spring your boat is ready for action and you won’t spend valuable time at sea repairing the winters damage.


So, what do you need to do?  Let’s start with the easy stuff. The wiring inside most boats generally consist of two types. The boats original wiring will probably be in pretty good condition even if it is 20 years old. The added in bits however are a different matter. This is where a lot of problems occur. Poor wiring and materials can lead to small current drains especially when the damp sets in. If an area gets particularly damp the current flow can increase to a point where the Positive wire dissolves. Now this isn’t always dramatic. Over the winter tiny breaks can occur leading to hours of trouble shooting in the spring. The most common area for this to happen is the bilge pump. Of course, it’s a good idea to leave the automatic bilge pump switched on but this means that the positive wire is always live. Bilge pumps are very rarely wired using the correct techniques and this wire frequently fails. Not dramatic, but of course the pump will not work. I said that this is the easy stuff. All you need to do is to make sure that any circuits you don’t need are switched off. This includes the engine.  You also need to check the bilge pump wiring to ensure that it meets the correct standards.  If you have any doubts why not ask for an Electrical Check. The check is carried out by a BMET qualified technician.

Now for the batteries.  Batteries are a very complicated subject and a quick look around various forums confirms that they are seriously misunderstood.  The first thing to check is that your batteries are in a good condition. There are lots of fancy testers out there, but the easy way is to charge them all up, disconnect them, and check them a day later. You can use any accurate voltmeter, and these days you don’t need to spend a fortune. If you check them the day after you have fully charged them, and the voltage has dropped below 12.8 volts you have a problem. The other thing to note is that they should all be the same voltage. If not, then you could be storing problems and not power.

Let’s assume the batteries are all good, what’s the best way of looking after them? In an ideal world you would take then home and give them their own easy chair in front of the TV. At the very least keep them warm and dry. In the real world they would probably stay on board. The best way of looking after them on board is to leave a charging source on all the time. Make sure that your battery charger is a good quality modern charger that is capable of float and storage charge.  A cheap, automotive, or old charger will probably do more harm than good. Then you must depend on Shore Power, but we will look at his later.

Another way is solar. Solar yield in the winter especially on the Cumbrian Coast is not the best, but it is, even with a modest solar panel, good enough to keep the batteries topped up. The trick here is to fit a really good quality MPPT solar regulator. The Victron Smart controllers will look after your batteries and even show you how much the solar has contributed via the Victron Connect App. Using cheap controllers or connecting solar panels directly to your batteries will ultimately destroy them.

Shore power may seem like a good idea and most of the time it is. However, it’s not without problems. The first problem is that once you plug in to shore power the earth wire connects all your under-water metal bits to everyone else’s underwater metal bits. Since you are all sat in an electrolyte called seawater the entire marina effectively becomes a very large (but very low voltage) battery. So, if your underwater metal bits are at the wrong end of the periodic table they will start to dissolve. Worst still if someone in the marina has a DC fault then your expensive metal bits will start to dissolve very quickly.  It’s worth checking to see if you have a Galvanic Isolator fitted. If not, it would be a good idea to get one fitted. There are two types the lower cost Diode type, and the Isolation Transformer. If you have the diode type check that it is still OK. It’s not unusual for these to fail if you have ever had a major earth fault on board.

The other problem with shore power is reliability. Sea water and 240 volts are not a good mix, and the marina installations can fail, even when they are regularly maintained by the marina. The most common failure is the shore power lead. The plugs that connect to the bollard are very prone to failure. They cost just a few pounds and if you are in any doubt get them replaced. Other things to look out for is exposed cores (the Brown, Blue and Green /Yellow) showing. Cable that is too large (usually found on imported American Boats), and the wrong type of cable, it should be Blue Arctic Grade or marine grade rubberised. Make sure that the cable is not coiled, up, this can make the cable hot and then it will crack. Finally use a rope to tie the boat to the Dock and not the cable, the cable should never be wrapped round cleats either on the boat or the Dock.