27 February, 2017
Sight glasses in tanks to measure the fuel level are wonderfully simple and clear and do not need electrics which is always a bonus on boats. However they are often poorly installed making them a safety hazard.
A poor installation often consists of a length of nylon pipe or PVC hose coupled directly to the tank top and bottom as shown in the picture at the top.
Normally the pipe is not fuel grade and will become cloudy as the fuel degrades it. If the tube is damaged and broken by a knock from loose objects in the locker it will empty your tank and leave you with a dead engine. In the worse case scenario, a fire melts the tube and continues to feed the fire with the contents of your tank and there is nothing you can do to stop it. In the tank on above, that’s 157litres of fuel in the bilges.
To correctly install a sight glass it should be fitted with a self closing valve at the bottom and top so that in the event of the tube breaking - or melting - the fuel will not empty from the tank. The self closing valve in the bottom picture was reasonable cost from Aquafax and simple to install. The sight glass is protected by a metal cover and still clear after 3 years in use.
Just remember push the button each time you need to check the fuel level as it will continue to indicate the last reading.
18 February, 2017
Seacocks connected to below the waterline fittings such as bilge pumps or sea toilets can be prone to back flooding by siphoning. If the seacock is left open or has a small leak past the seals then it is possible for the vessel to slowly flood and sink.
Having witnessed a vessel taking on water due to siphoning, I can confirm for a relatively small outlay they are definitely an invaluable safety item! Never rely on one-way valves as I have seen on boats. In my experience they will fail to seal properly after about 6 months.
Swan necks should rise above the sea level by at least 8” or 200mm when heeled over. In practice this is normally limited to below the side deck. The anti-siphon valve is a small one way valve inserted in the top of the loop that is normally closed. When you finish pumping and the water level tries to drop back to sea level and small vacuum is created inside the loop which forces the valve open and allows air into the pipe. This breaks the siphon and prevents water flooding back into the vessel.
Swan necks on their own will not prevent back flooding, you need the anti-siphon valve as well to allow the seawater side to fall back to sea level.
The small valve is often a small rubber moulding under a screw cap and it requires regular cleaning to keep it working. Never use Vaseline on these or any other rubber seals as it deteriorates the rubber, use a silicon based grease.
7 February, 2017
Corrosion has been the enemy of boat owners for centuries and can cause severe damage to underwater metal fittings if not controlled properly. It is caused by the exchange of electrons between two different materials when in an electrolyte such as seawater. The material that gives up its electrons is called the anode and the material that receives them is called the cathode. The anode will loose material and the cathode will be coated by them.
There are two main types of corrosion to worry the boat owner, these are electrolysis & galvanic corrosion. Galvanic corrosion is caused by two dissimilar metals being in an electrolyte solution and causing electrons to flow which leads to corrosion of one of the metals. Electrolysis or stray current corrosion is caused by one of the metals being charged by a different electrical voltage. This can happen due to a wiring or equipment fault or even a fault on the wiring of the boat moored next to you!
Galvanic corrosion can be prevented by the fitting of sacrificial anodes to the hull in strategic areas. The anode material should be selected to suit the salinity of the water the vessel is cruised in and should have enough surface area to protect the vessel's metal work below the waterline. MGDuff a well known producer of anodes offer an excellent online search facility to choose the correct anode and a helpful database. The anodes should be inspected annually and replaced when they are 50% depleted.
Electrolysis is more of a problem and can cause severe corrosion very quickly even if you have galvanic isolator fitted on board. The propeller in the picture below was fitted to a yacht with a galvanic isolator but still suffered electrolysis so severe the propeller as beyond repair and had to be replaced. This type of damage will often only become apparatent when the vessel is lifted for its annual inspection or repair. If electrolytic damage is found it is worth conducting a test for stray voltage in the water around the vessel by hanging a silver chloride reference cell with a multimeter to determine if there are stray voltages at each skin fitting.
The main signs to watch out for when inspecting your underwater metal gear are a slight pink tinge to the surface colour and pitting of the surfaces. These symptoms indicate that there is something amiss that requiring closer investigation to prevent serious damage occurring. Contact your local yacht surveyor or speak to a qualified marine electrical engineer to discuss the problem and find a solution.
24 January, 2017
Fire extinguishers are one of those items like most safety items that you only use when you really, really need them! I have surveyed many boats with extinguishers that are out of date and often have no pressure in left in the bottle so they are only good for ballast and in the case of the extinguisher in the picture, not even safe for that.
As a guide, extinguishers should be serviced annually to make sure there is no corrosion, that there is pressure in the bottle, and the powder has not 'caked' solid in the bottom. They should also be replaced every 5 years.
Getting only a few extinguishers serviced can be difficult as its not worth the engineers time to for the benefit. However most boats are kept in marinas and yacht clubs that all need extinguishers on the pontoons serviced so why not speak to the yard manager or secretary to see if yours could be done at the same time. If that is too difficult to arrange maybe a few boats clubbing together to bring a service engineer down would be more economical.
9 January, 2017
Standing rigging are the wires and lines that hold the masts and spars in place. These days they are nearly always made from stainless steel wires and secured in swaged fittings because they are are strong and relatively reliable. However most insurance companies give standing a rigging a service life - normally about 10 years. After this period the rigging is considered outside of its service life and therefore may well not be covered in the event of an insurance claim.
During a survey I will inspect the rigging as far as possible without the mast being lowered. This includes checking all the wires in the cable, the swages and bottle screws. Sometimes wires can become damaged such as the one in the image above and these are obvious to spot however, the danger often lies within the swage. This is because stainless steel is only stainless when its in the presence of oxygen which gives is the oxide layer on the surface that prevents corrosion. Inside a swage the oxygen can become depleted and so the stainless steel can now corrode, unseen and giving no warning. The insurance companies look at the data for rigging claims and know that after 10 years, claims increase so they take the obvious step of giving it a service life although this not normally written down anywhere. It is for this reason the rigging should be replaced every 10 years.