boats at Aqueduct Marina and Brokerage

Aqueduct Boat Services

Information – Click on the headings below to find out more information


Hull corrosion is the bane of steel boat owners and it is important to take as many steps as possible to minimise it. Whilst blacking does much to reduce corrosion, it is inevitable that some will get removed through contact with locks, banks etc.

As soon as the steel is exposed it will start to corrode (rust), but the effects can be minimised by the use of anodes. So how do they work? Basically, if two metals are in a conducting liquid, i.e. water, and connected together a current will flow between them. This is how a battery works. As water is a poor conductor the current will be very small, but as it is there 24 hours a day, 7 days a week the cumulative effect can be significant. On a boat brass skin fittings, a brass propeller and even slightly different grades of steel can all effectively become the plates of a battery and as metal will be removed from one side by going into solution to release the electrons, corrosion will occur. This is the dreaded “galvanic corrosion” that gives rise to pitting. Note that this can be exacerbated by the use of a landline but this is a different subject (see “galvanic isolators” below).

All metals can be placed within a “galvanic series” which means that if two metals are in contact, the one higher in the series (more reactive) will dissolve in preference to the lower one. The further apart the metals are in the series, the more pronounced this effect will be. We can use this to our advantage by fixing lumps of a more reactive metal to the hull which will then act as the anode in the circuit and dissolve in preference to the steel it is attached to. The metals used are zinc and magnesium, and it is important that the right one is used. Zinc works well in salt water due to the higher conductivity of sea water and the reaction with salt, but will be ineffective in fresh water where magnesium must be used. Conversely, magnesium will be too reactive in salt water and will be used up too quickly.

On a narrowboat, it is normal to weld four 2.5 kg magnesium anodes to the hull in the swims where they will not come into contact with lock sides etc. They can be expected to last about two years and it makes sense to replace, or add to, them when the boat is blacked. Aqueduct Boat Services carries magnesium anodes in stock and can arrange to have them fixed whilst your boat is out of the water.

The protection afforded by anodes has a limited range and for this reason some boats have additional anodes fixed to the middle of the hull, but these will need protecting from being impact damage.

Galvanic isolators

When boats are moored in a marina they tend to share a common 230V electrical supply. As it is normal for the boat’s hull to be bonded to the electrical supply earth, this means a circuit can exist between two boats, linked by the water and the common earth connection. So far so good, but problems arise if one boat is at a slightly different potential to another. Different metals in a conducting medium like canal water effectively makes a battery, so when the circuit is completed by the earth connections a current, albeit very small, will flow round the circuit. This causes metal to be dissolved and although the current is very small, it is present 24 hours a day, 7 days a week and the cumulative effect can be significant. Even different grades of steel can be enough to create a current which can lead to pitting in the hull material.

The effect created by two different metals can be used to advantage by fixing anodes to the steel hull. This way the corrosion will occur on the anode rather than the steel. However this is not enough to prevent corrosion of the steel completely, and also in a marina the anodes can corrode very quickly by trying to protect neighbouring boats or even metal pontoons.

In order to prevent this corrosion it is necessary to isolate the earth connection, but doing this would put the safety of the boat at risk. The answer is a galvanic isolator (G.I.). The voltage generated by the dissimilar metals is only very small, and the G.I. blocks the low voltage currents. If a fault did develop in the on-board 230V system, the higher voltage can overcome the G.I.'ss blocking effect and still allow the dangerous voltage to go to earth, thereby tripping the circuit breaker.

Due to the number of electrical items used on board these days, it is possible for small induced voltages to overcome the blocking effect of the G.I. Most G.I.s now are set to a higher voltage to prevent this. The alternative is to fit an isolating transformer to block the earth currents. This will completely block DC earth currents, but is a much more expensive option.

For the large majority of us, a G.I. with a blocking voltage of over 2 volts will be more than adequate. They are not expensive and can usually be fitted in under an hour. If your landline is not protected, we strongly recommend having one fitted and Aqueduct Marina has qualified electricians on site who can do this work.

Engine servicing

Just like a car, it makes sense to have your boat’s engine regularly serviced. As well as keeping the oil clean and maintaining its lubricating qualities, the service allows other filters to be checked and gives an opportunity to check the overall condition of the engine.

Service intervals vary between suppliers and typically range from 100 hours to 250. With the shorter interval, often just an oil and filter change will suffice, with a more extensive service carried out every second or third time. Similarly with fuel filters, the external pre-filter can be changed at 100 hours with the engine-mounted filters changed every second time. What you do will depend on the make of engine, its age and the supplier’s recommendations.

Time of year can also influence when to have a service. Oil will absorb some water as well as sulphur residues coming from the diesel. This can cause acids to build up in the oil which can cause corrosion to the engine and injector pumps. It therefore makes sense to do an oil change before leaving the engine unused for an extended period, e.g. over the winter.

At Aqueduct Marina, we have experience of a wide range of modern and vintage engines and can advise you on what servicing program is best for your engine. The cost of a service will vary depending on the type of engine, how long the service takes and what consumables are used. A full service will cover items such as oil and filter change, fuel filters and a full external check of the engine to include things like cables, engine mounts, cables and stern tube.

Battery life / charging regimes

Batteries are probably one of the most abused items on a narrowboat. With inverters, fridges and electronic equipment, more demands than ever are being made on the batteries.

Two significant things will shorten the life of a battery: running it completely flat and not fully recharging it. Whilst the former sometimes occurs, failing to fully recharge batteries is by far the commonest reason batteries don't last, especially if the boat does not have an electric hook-up and charger. It is recommended that batteries are not taken below about 50% charge. If you have a typical 400 AHr capacity, this means that 200 AHr may need to be replaced. On a typical 80 – 100 A alternator, about 50% of this will be replaced in the first couple of hours (the alternator output soon starts to drop below the maximum output). As the voltage of the batteries rises the current decreases and so the next 30% might take 4 or 5 hours to replace. The last bit will take several more hours. An alternator controller can help to reduce the charging time, but it can only do this by increasing the voltage of the alternator and the higher the battery voltage gets the lower the current will be. There is a limit to how high the alternator voltage can go without damaging the batteries so even fancy controllers will take several hours to replenish the batteries.

When the batteries never get fully recharged they will suffer from sulphation, which effectively reduces their capacity until they are no longer viable. There is little that can be done to recover them at this stage and replacement becomes the only option.

Whilst the voltage of a battery is easy to measure, it doesn't always tell the true story. What is significant is what the voltage is under load and there are specialist battery testers which will do this.

So, the key to good battery life is to keep them charged up as much as possible and don't let them go flat. If you don't have access to a shoreline, a solar panel or wind generator can help to top up the batteries when the boat is not being used.

Diesel bug

What is widely referred to as “diesel bug” is actually a range of bacteria, yeasts and moulds that grow in the fuel tank. The bugs can arrive through contaminated fuel or just drift in through the tank vent. Once in your tank, if conditions are suitable the organisms will start to multiply and this is what gives rise to the problems. The organisms live on the water / diesel interface, living in the water and feeding on the oil. The inclusion of biodiesel just makes the oil that much more palatable, so problems are likely to increase.

The organisms will multiply rapidly but die off quite quickly. However the dead organisms build up into a black or brown sludge and it is this that can block the filters and cause fuel starvation. Two things are necessary for the bugs to thrive: water and oil. Therefore the easiest way to reduce the impact of the diesel bug is to keep water out of the fuel tank. This is easier said than done, as condensation will form on the top and sides of the tank and run down into the fuel where it will sink to the bottom and gradually build up. Keeping the tank topped up, especially in winter, can reduce this, but some water build-up is inevitable. The other method is to use a fuel additive which will help to alleviate the problem. These work in two ways; firstly they contain a biocide which will kill the organisms in the fuel. Secondly they will help to disperse the water in the fuel and so remove the home of the bugs.

Symptoms of infection are: lumpy running, vibration, more noise than usual as though the engine is under load and poor starting. If this occurs it is necessary to start by changing the fuel filters and flushing out the fuel lines. The next stage is to remove as much water as possible from the tank. The best way to do this is with a pipe and suction pump, as tank drains and draw-off pipes will not normally reach the bottom of the tank. Once this has been done a fuel additive can be added if the fuel itself still looks reasonably clean.

It is still not clear how the diesel supply industry will address the problems of biodiesel in the marine environment. Initially it was expected that low sulphur fuel, a legal requirement in 2011, would basically be white diesel with a dye added and therefore contain biodiesel. However now that the potential problems of storage and use on boats would create problems, the industry is looking at ways of supplying red diesel without biodiesel added. Whilst this will help reduce the risk of diesel bug contamination it will not remove it completely, so good practice is still needed to keep your fuel clean.


Regular blacking is important to reduce corrosion on the hull. The normal interval is around two years and it is also a good time to check and replace anodes. Your first decision is whether you want it done for you or do it yourself. If you decide on the former then a boatyard would normally put the boat into a dry-dock, pressure wash and scrape the hull and put on two coats of standard blacking. If the anodes need replacing it makes sense to do this at the same time. There are alternatives to the standard blacking e.g. Comastic or Two-pack. The latter will last a lot longer than normal blacking although it is still susceptible to physical damage. This could also be a good opportunity to have the gunwales and tunnel bands repainted. At Aqueduct Marina we have the facilities for blacking and also have a professional boat painter on site who can discuss your requirements with you.
Boat Painting

Should you wish to do the job yourself some boatyards will hire out their dry dock or put the boat on hardstanding for as long as you need to complete the job. Normally the boat yard will offer a pressure-washing service which will reduce the amount of preparation considerably. It is important to let the boat dry completely before applying the blacking and also give it an opportunity to harden off before going back in the water. Normally a week is enough to prepare the hull, apply two or three coats of blacking and allow it to harden before going back in the water. Whilst the boat is out of the water you can also carry out any other maintenance needed. Here at Aqueduct Marina we carry a wide range of engineering supplies and also have experienced staff on site who can advise you and carry out the work if you would rather have someone else do it.
Slipway / Hardstanding / Workshop Hire


These days boaters are wanting to run more and more equipment on their boats. Whilst much is available that runs on 12 volts, some equipment is only available on 230V or is much cheaper in that format. As a result many boats are now fitted with inverters to run 230V equipment from the DC supply.

Inverters come in two main flavours: Pure Sine Wave (PSW) or Modified Sine Wave (MSW). The latter may also be referred to as Quasi Sine Wave (QSW). PSW inverters try and replicate the smooth waveform that is supplied by the mains and should run all equipment within its power range. The MSW has a simpler waveform which will run most equipment but some devices, particularly those with electronic timers, may have problems and interference may be experienced on radios & TVs.

Inverters come in a range of powers from 100 watts or so up to 3Kw. When deciding what size you need, it is important to allow for the start-up current. Devices with motors such as fridges draw a much higher current when starting up and whilst inverters generally can supply a higher current for a short period this can still lead to problems. Remember also that microwave wattages are output power not input, so typically a "700W" microwave will actually draw nearly double that figure.

Inverters need to be kept dry so putting one in the engine 'ole under a cruiser stern is not a good idea. They also need good ventilation and be mounted as near to the batteries as possible. They can draw very high currents from the battery, for instance an inverter delivering 1000 watts can be drawing nearly 100 amps from the batteries. Short thick cables are therefore essential with an appropriate fuse and be connected directly to the battery posts via an isolator switch.

More sophisticated inverters can incorporate other functions and can be used as a battery charger when connected to a landline. Whilst the output is normally separated from a landline power source, some can be used to top up the available power and switch over automatically. It is also very important that a residual circuit breaker is fitted and this must be wired up correctly for a boat. The way this is done is different to a land-based setting and so it is essential that the electrician doing the installation is familiar with marine mains installations, to protect both the boat occupants and people outside the boat.

Stern gear / prop checking

Problems with the stern gear usually show up as excessive vibration of the rudder and/or the engine. Causes include worn rudder bearings, the rudder loose on the rudder stock and bent propellers.

If you think you have excessive vibration the first thing to check is that there is nothing caught on the propeller or prop-shaft. The next thing to check are the engine mountings to ensure the engine isn't rocking or loose.

If the stern gear needs closer inspection the boat will have to come out of the water. If it is just an investigative look, the boat can be taken up the slipway on the purpose-built trailer, and if the boat is returned to the water within two hours, only one slipway charge will be made. If the boat has to come out for longer, we can put it on hardstanding for as long as you need to effect repairs.

Although the design of a narrowboat's stern and skeg offers a good degree of protection to the prop, it can still be damaged by hitting underwater objects. A surprisingly small amount of damage to the leading edge of a propeller blade can cause a significant amount of vibration which, as well as being annoying, will put pressure on the stern tube and engine which can lead to further damage so repairing as soon as possible is highly recommended. The propeller can be sent away for reprofiling if it is not too severely damaged, or a new one can be fitted. Although we do not stock propellers we can get them delivered quickly and can fit them if required.

Rudders are normally fitted with a very simple plain bearing at the lower end which is subject to wear. Usually the rudder stock can be sleeved to take up the slack, or a new cup fitted to the skeg. The upper part of the stock is usually fitted with a roller bearing and these can be replaced if required.

If you have a packed stern tube, this might be a good opportunity to have the packing replaced. This is an easy job whilst the boat is out of the water although it can be done in the water. All such services are available at the marina or you can do the work yourself.


Recent cold winters have seen periods of sub-zero temperatures and as a result a number of boats have been caught out. Whilst a brief overnight frost will do little damage, several days of freezing temperatures will guarantee that water inside a boat will get frozen.

You can minimise damage by leaving taps open and making sure shower mixers can drain freely by disconnecting the hose, but the only way to be certain of protecting your plumbing is to completely drain the system. Experience at the marina has shown that the most vulnerable items are shower mixer valves and water filter bowls. You should check these are empty of water even if the system has been drained. Whilst it is not normally necessary to completely drain water tanks, it makes sense to isolate them from the rest of the system so that if a leak does occur it won't drain the contents inside the boat. The calorifier however is vulnerable so make sure that has drained properly. Remember that insulation will not prevent freezing, but only delay it. If it is not possible to completely drain the system there are non-toxic antifreeze additives that can be added.

Don't forget the central heating system. Normally the system will be filled with a water / antifreeze mixture in the same way that the engine is protected. However be aware that if you have topped it up then the strength of the antifreeze will have been diluted. It is a good idea to keep a bottle of ready-mixed antifreeze for topping up; this will also reduce the risk of neat antifreeze affecting the circulation in the radiator circuit if the antifreeze level needs increasing.

Aqueduct Marina offers a winterising service if you are unable to do this yourself. 2010 saw severe frosts at the end of November, and whilst this was exceptionally early, don't leave it too late to drain your system or arrange for it to be winterised.

Calorifiers / accumulators

The calorifier is the boating equivalent of a domestic hot water tank and stores water heated by either a boiler or the engine. They can also be fitted with immersion heaters for use on a landline.

Two formats are available, vertical or horizontal. The former are generally considered to be more efficient but being about a metre tall need a suitable cupboard space. Horizontal calorifiers can often be fitted under the bed or on the swim beneath a cruiser or semi-trad deck and so utilise space that may otherwise be wasted. Both types are available in single or twin-coil versions where the former would be used if heating is only supplied by one source whereas the twin coil version allows the water to be heated by both the engine and boiler. The bottom coil should be used for the most-used source of heat, so if you cruise regularly then the bottom coil should be connected to the engine but if you tend to stay put and use a boiler for heating then connect the bottom coil to that.

Care needs to be taken to prevent the hot water losing heat to the engine at night by a thermosyphon effect. This can be done by careful routing of the pipes or if necessary by incorporating a flap valve in the engine heating circuit. The effect is most pronounced with horizontal calorifiers fitted at floor level.

Calorifiers are normally made of copper with foam insulation. However if the boiler contains an aluminium heat exchanger, e.g. the Alde 3010, then the amount of copper in the system should be minimised and a stainless steel calorifier used. All systems should be filled with a 25-33% antifreeze mixture to reduce corrosion and prevent split pipes or radiators in the event of a freeze. Always mix it thoroughly before filling the system, otherwise different concentrations, and thus densities, may prevent radiators getting hot. Top up the system with a mix of similar concentration for the same reason.

A significant amount of expansion will occur when the water is heated so it is vital to have a pressure relief valve fitted on or very close to the calorifier. To prevent water leaking continuously through the valve, an expansion vessel can be fitted to absorb the increased volume. This consists of a steel canister with a rubber diaphragm inside with air above, fitted into the hot side of the circuit. It is also sensible to fit an accumulator, which is exactly the same device, but fitted into the cold water feed. In this case its purpose is to smooth out the pump flow and stop the pump cutting in and out at low flow rates. Whilst in this situation it would also absorb expansion in the calorifier, it is usual to fit a non-return valve in the calorifier feed to prevent hot water being drawn back into the cold water pipes and this would prevent the accumulator absorbing the hot water expansion.

Water heated by the engine can get very hot, much hotter than in domestic hot water systems. To reduce the risk of scalding a thermostatic mixer can be fitted to the hot water outlet of the calorifier. This will mix the hot water with cold if required to supply water at a lower temperature. This is highly recommended if children will regularly be on the boat.

Toilet systems

It is said that when three or more boaters get together, within 15 minutes the conversation will come round to toilet systems. There are two main types of boat toilet, and each has its supporters and detractors.

The two main systems are pump-out and cassette. The former consists of a holding tank, usually installed under a bed, which requires pumping out periodically. Older systems were "dump-through" where the toilet opened directly into the tank. Nowadays the waste is usually put through a macerator and pumped to the holding tank. Whilst this keeps the holding tank out of the way, it is more prone to problems due to blockages and pump failures.

The most basic type of cassette is the "Porta-Potti" which uses a small reservoir of flushing fluid. Most are now replaced by cassette systems that are plumbed into the water supply and use fresh water for flushing. Their volume is limited by the physical handling of the cassette so are usually around 17 – 20 litres capacity.

Most boat yards offer pump out facilities and some BW sanitary systems also have self-service pumpout machines operated by pre-purchased cards. It is also possible to get self pumpout kits but there are limited facilities for using these as BW Elsan disposal points must not be used. Pump-out costs are typically around £15 – £20.

Cassettes can be emptied in Elsan disposal points which are found regularly around the system. These are normally free but do require you to handle the full cassette yourself, which can weigh about 20 Kg when full.

As previously mentioned, each type of system has its supporters, and which one is best for you comes down to personal choice. Are you physically capable of handling a full cassette? If you have a pump-out will you always be able to get to a pump-out station? How well-acquainted to you want to get with last week's dinner? The choice is yours!

Stove installation

The requirements for solid fuel stove installations are currently being reviewed by the Boat Safety Scheme.

In the meantime, care should be given to installing stoves in narrowboats as they are probably the biggest cause of fatal accidents on the canals. Having said that, a sensible installation will provide an economic source of heat and stoves are installed in thousands of narrowboats across the system.

The most important thing is to make sure the surrounds are fully fire-resistant. Tiling onto wood is not sufficient and where this had been done, charred wood is frequently found behind tiles when they are removed. Whilst tiles provide an acceptable fire-resistant surface, they must be backed by insulating and non-flammable material. Also, sufficient air-gap must be present between the exterior of the stove and the fire surround unless the fire is specifically designed to be fitted into a space, e.g. a corner.

As well as the fixed surroundings, care should be taken to ensure that inflammable fittings such as curtains and carpets are nowhere near the stove. Lastly, leaving a pair of wet gloves or socks on a stove to dry out is asking for trouble as it is all too easy to forget they are there.

The second significant risk that can result from poorly installed stoves is carbon monoxide (CO) poisoning. CO is an odourless gas with a similar density to air so it can be present without anyone knowing about it. The effects are cumulative and can be fatal. Symptoms include headaches and flu-like symptoms. CO can leak from a stove through poorly fitting doors or chimney collars. If smoke can escape from the stove then so can CO. A CO detector in the boat is strongly recommended (and should also be fitted if you have gas appliances even if you do not have a stove), and preferably one that will give a digital reading.

An alternative to solid fuel is to fit a diesel stove. These take many forms and some are almost indistinguishable from a solid fuel stove, but without the hassle involved in fuelling and cleaning up a solid fuel stove. Diesel oil can be drawn from the same tank as the engine, but it is better to have a separate tank, usually fitted at the front of the boat. It is important that the fuel is kept in good condition and the stove should be serviced regularly.