ALL ABOUT ANODES FOR LEISURE BOATS

” Plus Bonding Systems “

How do sacrificial anodes help keep your boat in good condition and possibly afloat

Pictures   –   Hull anodes that     ” No longer have sufficient mass to be effective “

In a few words, how galvanic corrosion works.

Any two dissimilar metals submerged together in an electrolyte – sea water in our case – will create an electrical current known as a galvanic cell (like a battery), with the less noble (more active) metal, a bronze propeller for instance, forming the anode and the more noble (less active) metal, a stainless steel shaft, forming the cathode.  The electrical current will travel from the less noble metal, anode, to the most noble metal, cathode, depleting the anode from its core material in the process.

The bronze propeller will gradually corrode away and this is where trouble will start.

The way around it is by adding a sacrificial anode to the system.

This anode will need to be made of a more active metal than the other two and thus the bronze propeller will now become a cathode and be protected.

That’s all fine when looking at a simple assembly such as a prop and prop shaft.  Stick an anode on the shaft and that is generally sufficient but how about a bronze seacock and through-hull fitting?  Not very practical to stick an anode on each one of them.  So the answer is to electrically bond them to the anode.

All immersed metal components should be connected to the cathodic protection.  Many ingenious systems exist to bond the engine, prop shaft and propeller and you should see with your engineer what would be best suited for your boat.

Anodes on non ferrous boat are generally bolted through the hull.  Easier than welding onto a GRP hull or a wooden one!

But that’s great because now we’ve got two studs inside the boat connected to the outside anode.  So now we can wire (bond) the seacocks to the anode’s studs, and the engine and prop shaft to another, or the same one depending on the size of the boat, and the amount of dissimilar metal within close range of each other.  One thing to remember is that anodes can “see” the parts to be protected so long as the circuit is not broken.

A few things to look at when connecting them is that the connection is well made and kept on the inside of the hull and clear of bilge water.

Also, when you pop your head down the bilge, have a quick look at the connection as the bond might be broken due to galvanic corrosion and now what you were thought was protected by the anodic circuit is now isolated and will corrode.

Different Waters    =    Different Anodes

Three different types of anodes can be used:

• Fresh water                         Magnesium
• Salt water                            Zinc
• Brackish water                   Aluminium

The surface of a zinc anode when left in fresh water for some time become covered with an off-white crust.  This will effectively seal the anode and stop it working when it is returned to the salt water.  The consequences are that the next most anodic item bonded to the anode will start to sacrifice itself.  It is therefore important to check the anodes after trips into fresh water.  Also, if keeping the boat on the Norfolk Broads or brackish waters, aluminium anode would be a preferred choice to protect the vessel.

It is important to have them replaced when they reach ~50% of their original mass as the rate of galvanic corrosion is accelerating and your protection diminishing.

For Information: Very rapid zinc anode loss that results in bright, shiny metal being exposed is a clear indication of electrical activity, be it galvanic or stray current, usually the later, since galvanism rarely creates enough current to destroy zincs quickly .  

Bright zinc in association with heavily corroded bottom paint means you have a problem that needs to be addressed immediately. The brightness of the zinc is telling you that there is too much current for the zincs to handle. Adding more zinc is NOT the solution

Earthing – Bonding Systems:  

The purpose of a bonding system is to equalize the electric potential of dissimilar underwater metals by tying them all together with wire or copper straps. The benefits of a bonding system are wide ranging but little perceived. One is that it serves to dissipate stray current leaks. 12 volts of current focused on a small piece of metal will result in rapid destruction.

But that same 12 volts spread over a much larger surfaces, causes less damage in proportion to the size of the water exposed surfaces of the metal. Bonding systems can reduce the corrosion potential of metals inside and on the bottom of the boat.  

Vessels which have all the hardware bonded, such as the railings, will suffer much less corrosion. The general rule is that anytime a piece of metal plumbing or hardware is isolated in a system, as with a sea strainer that is joined by two hoses is electrically isolated, needs to be wired into the system.

This can be done by daisy chaining items together, but it’s a good idea not to include too many items in a chain. Obviously, at any point where a connection is broken, all those items upstream will be unprotected.

DC Current leaks are the most common form of a stray current problem

Yes I know,  We’ve just added another box to your winter maintenance tick list  But hey, they need to be looked after.

Stern Drives,   Outboards   &   Sail Drives

Now for those of you with a sterndrive, outboard or saildrive, things are bit more sensitive.  See an earlier post  SeaRay 290 Sinking – Mercruiser Stern Drive Investigation

As they are made in aluminium for lightness reasons, although of a high quality they are very prone to galvanic corrosion.  It is very important to keep all the anodes in good condition i.e the anodes are depleting and not the stern drive casing.  I often found that the little braided wire connecting the casing to the anodes was broken so make sure to keep the connection live!

Although the standard propeller is generally made of aluminium on those units it might have been replaced by a stainless steel prop for better performance, thus changing the situation.  You will need to review your cathodic protection and install an extra and bigger anode.

Another silly one is when the ‘sport’ boat is moored, the sterndrive is often kept out of the water, which in some ways is a good practice.  But on some boats the leg cannot be fully titled out of the water, leaving the gearbox partially immersed while the anodes are nicely dry in the sunshine enjoying their holiday and not doing much to protect the gearbox.  It will lead to a rapid deterioration of the gearbox casing and resulting in water ingress.

To overcome that issue you can either fit an extra anode on the transom or hang some over the side of the boat (in the water) close to the leg.

Someone once told me that you can only have over protected your boat when it sinks from the weight of the anodes!

But most of all remember that a painted anode doesn’t work at all  You can see the evidence by the end of the season when the anode is still painted and your prop is almost gone!

Now here is a simplified galvanic series.  Platinum is pretty much up there on top of the noble metals but I thought I would stick to materials actually used in boat building just to keep it relevant to us.

Steel Hulls / Cathodic Protection 

Currently most UK canal boats do not have enough anodes fitted to provide protection to all of the hull. Often we see vessels of considerable length (60ft plus) with only 4 hull anodes fitted. Typically 2 at the bow and 2 at the stern. Our literature has perhaps not helped as we do show vessels up to a wetted surface area of 56m2 with 4 anodes for protection and vessels up to 70m2 with 6 anodes. I would suggest that all vessels should as a minimum have 6 anodes, and as the vessels get longer in length they should have 8. I will be looking at updating our own literature to reflect this.

From a technical point of view an anode will only “throw” its protective current roughly 7 times its own length, which is why anodes are required to be equally spaced along the hull of the vessel to ensure good coverage. From this you can see that just fitting 4 anodes to a typical canal boat is not adequate protection for the entire hull. I suspect that most pitting corrosion you see is at the mid ships position, as this is the furthest point from the bow and stern mounted anodes.

The flip side to the argument for better cathodic protection is possibly that most canal boats operate in fresh water and this is a far less aggressive medium to salt water. Plus that anodes are used to provide a back up to a good protective paint system. However I still feel a belt and braces option is always best and especially verses the cost of hull plating.

Galvanic Series:

In this sample list, the metals and alloys are arranged in order of their potentials, measured with reference to an electrode immersed in salt water.

The list is arranged 00 – 12 with the least noble metals # 12  (ANODIC)  at the top end and the most noble # 00  (CATHODIC)  at the bottom.

ANODIC                                                      MOST ACTIVE

12:                                                                 MAGNESIUM ALLOYS

11:                                                                 ZINC

10:                                                                  GALVANISED MILD STEEL

09:                                                                 ALUMINIUM ALLOYS

08:                                                                 MILD STEEL

07:                                                                 LEAD

06:                                                                 GUNMETAL

05:                                                                 MANGANESE BRONZE

04:                                                                 NAVAL BRASS

03:                                                                 SILICON BRONZE

02:                                                                 COPPER

01:                                                                  MONEL

00:                                                                 STAINLESS STEEL

CATHODIC – NOBLE                           PASSIVE  / LEAST ACTIVE

For more information contact European Marine Services Ltd.  Marine Surveyors & Consultants 
EMS also undertake Boat Safety Inspections & Engine Inspections

www.europeanmarinesurveys.com
Tel: 01603 327 123

OSMOSIS  &  WICKING

Picture 1   Sample – Small osmosis blistering showing a high moisture content reading

Very simply, the problem is caused by water penetrating the gelcoat and entering the laminated structure. This water takes in solution free chemicals salts and becomes denser than salt water on the outside of the hull. This creates a differential pressure and since water will not compress blisters form on the outer side of the gelcoat

Unfortunately the development of blisters is not predictable, some vessels may indicate high moisture content, suggesting the presence of blister fluid, but will not develop blisters for many seasons if at all, others may have similar readings with blisters present. It is generally accepted that osmotic blisters will not be found with ‘low’ meter readings – though this is not always true. Not all blisters are caused by osmosis, some will be found to be dry blisters, these may often appear in the gel coat and usually caused by aeration when the original batch of gel coat was mixed.

These swell with water and raise localised rashes on the gel coat which disappear after a short time ashore and usually of no consequence.

Blisters caused by osmosis particularly at the outset may not be easy to find, as they may not be very numerous and will be quite small, having the appearance of small pimples, on average they may reach fingernail size (approximately 10 mm diameter), in extreme cases these may reach hand palm sized or larger when many blisters merge and combine making very large individual blisters, although this is a rare occurrence on modern craft, and probably would have been attended to long before it had reached this size. Serious delamination would be a result of this extreme circumstance.

However, early treatment of osmotic boats in early stages tends to be less successful than treatments of vessels with advanced blistering.

Sample – Both small and large blistering

Experience has shown that the breakdown process in GRP laminates take some time to reach its conclusion, therefore if treatment is carried out prematurely, it is much more difficult to remove solutes from the laminate, and a reoccurrence of osmosis is much more likely to occur.

At the other extreme, a visual examination revealing extensive gel coat and deeper seated blisters may be all that is necessary to produce a diagnosis of “osmosis”. 

Photo 1 – The first osmotic blister was burst giving off chemical-smelling (blister juice) liquid – quite often under pressure, being acid and breaks down the polyester in a process known as hydrolysis – being normally localized.  The moulding as a whole will still retain most of its strength unless these current blisters become very much larger and much more extensive.    NOTE   The relatively low moisture meter readings obtained

Wicking:  Wicking is where the individual strands of the fibreglass mat behave like straws and draw water along their length, in doing so they swell in size and wicking will quite commonly be identified by a very slight raised pattern of the original matting visible on the gel coat.

Very often as the water dries out the swelling diminishes and the pattern disappears. When looking at a gel coat without pigment, wicking is easily identified because the area affected will have many individual strands of fibreglass clearly visible with a white outline.

This white outline is where the bond has broken between the resin and each individual strand. This ‘wicking’ is an indication that there is moisture in the resin, and is often a precursor to or accompanies blistering.

  Wicking

Treatments:

Do nothing. On an old, heavily built boat, this is a genuine option. If there are no blisters I would definitely do nothing even if a moisture meter shows very high readings. If there are blisters but they are small and not too many they are not likely to have any significant effect on the structural strength

Local treatment. Cut or grind open individual blisters, repeatedly wash out with hot water or steam, to remove the ‘blister juice’ from any blisters, dry thoroughly and fill with epoxy paste (not car body filler).

Hugo du Plessis, author of what is virtually the standard reference work on GRP yachts, regards this as the best option in almost all cases, and says total gelcoat replacement (see below) should be an absolute last recourse.

Next winter you may have a few more blisters – usually in different places. The fact that they are usually in different places is a significant one – you are not getting blisters re-occurring but new ones developing.

Go to your local ‘Osmosis treatment centre’ and pay rather a lot to have the gelcoat removed, the hull washed and dried out, and the hull recoated with epoxy. The smaller and older the boat the less cost-effective this is. Treating an old river cruiser could cost almost £4 – 5,000 on a boat perhaps only worth £15,000.

On a 50-footer worth £150,000 the cost might be £8,000 – a far lower proportion of the boat’s value. Yards used to offer a five year warranty with this work – many no longer do so, or charge extra if you want the warranty (they buy insurance against claims).

Osmosis Protection Scheme  Other protective measures that can be considered for ‘hull protection’ are to sheath with a water barrier such as International Gelshield 200 or VC Tar2 which is applied over existing gelcoat – however such applications cannot stop osmosis once it has started.  Such applications if applied following the manufacturer’s instructions are usually successful and can greatly extend the useful life of the hull structure.

Acknowledgement:   https://www.yachtsnet.co.uk/osmosis.htm

For more information contact European Marine Services Ltd.  Marine Surveyors & Consultants 
EMS also undertake Boat Safety Inspections & Engine Inspections

www.europeanmarinesurveys.com
Tel: 01603 327 123  

Investigations start following the death of two people from CO poisoning. “Each year boaters die or are made seriously ill from carbon monoxide (CO) poisoning – Boats are built to keep water out, but this also makes them good containers for gases and fumes.”

When carbon-based, appliance and engine fuels, such as gas, LPG, coal, wood, paraffin, oil, petrol and diesel don’t burn completely, CO is produced.

CO build-up in the cabin can occur with one or a mix of these factors:

• with faulty, badly maintained, or misused appliances
• exhaust fumes from a boat’s engine or generator
• escaped flue gases from solid fuel stoves
• blocked ventilation or short supply of air – fuels need the right amount of oxygen to burn safely

10 tips to keep you alive! Install fuel burning appliances properly Maintain appliances and engines routinely Use the equipment correctly Don’t allow engine fumes into the cabin space Deal with problems immediately Don’t allow bodged repairs and maintenance Install a CO alarm certified to BS EN 50291-2 Test the alarm routinely Never remove the batteries Know the signs of CO poisoning and how to react. For more detail read the information on the pages linked by the buttons on the left, or click next – How the silent killer works! or download the pdf booklet by clicking on the image on the right

Copyright belongs to the owners of the Boat Safety Scheme and CoGDEM jointly.

This information may be freely reproduced, except for advertising, endorsement or commercial purposes. Please acknowledge the source as Boat Safety Scheme & CoGDEM.

BSS Home

Boat owners are advised to avoid using portable gas appliances with integral gas canisters on board boats

Boat owners to treat all such portable gas equipment with great respect and change fuel canisters away from the boat and sources of ignition.Even portable gas equipment can cause an explosion big enough to send people to hospital.Escaped lpg from only one can form a flammable gas cloud the size of 250 cans.In the poorly ventilated, tight confines of a boat escaping gas is more dangerous than when it happens ashore out in the open.

An explosion on the Norfolk Broads saw two people taken to hospital for treatment for burns to their legs, hands and faces.The explosion happened when the gas canister of a camping stove was being changed in the open cockpit of a small sailing boat where candles and cigarettes were in use.

Think about the alternatives, for example, if all you want is a hot drink onboard a day boat, a flask is probably the simplest and safest way. If wanting light, some battery powered or wind-up LED lights will last for ages and are far easier to use than gas lanterns.

Where a simple cooker is needed aboard, think about installing a marine spirit stove as an alternative to a portable gas stove.

Anyone using a portable gas appliances has to be completely familiar with the correct and safe way of operating the appliance, from taking out of its storage case to fitting new fuel canisters.

• Only use portable appliances onshore.
• Stow the canisters, used or unused and any appliance if it has a canister inserted, in a self-draining gas locker, or on open deck where any escaping gas can flow overboard.
• Be familiar with the operating instructions before use.
• Before you start, check the appliance’s condition, if the gas canister seal looks damaged, or if the appliances or gas canister is extremely rusty and deteriorated, do not use it.
• To avoid gas leaks and carbon monoxide poisoning check that all equipment has been correctly assembled before turning it on.
• Never attempt to fit a new canister to an appliance when aboard, wait until you are onshore.
• Before fitting a canister, put out all open flames and smoking materials.
• Ensure that you have the correct type of gas canister for your appliance and that it is being inserted in the right place and in the right way.
• If you smell or hear gas leaking before attempting to light an appliance, don’t use it.
• If any gas is leaking, ensure that it is being dispersed in free air well away from the boat or any sparks or other sources of ignition.

Inland waterway regulations do not ban portable gas equipment on boats, but when not in operation, any appliance with a canister fitted and all spare gas canisters, empty or full, must be stowed in lockers that are self-draining, or on open deck areas where any leaking gas will flow overboard. The risk of causing a pool of explosive vapour inside the boat must be avoided.

Never use a barbecue (BBQ) on board a boat – take it ashore, enjoy it safely and avoid the twin risks of fire and carbon monoxideBBQing off the boat reduces the risk of setting fire to decks and on-board combustible materials from the heat from the red hot charcoal or loose embers.

When BBQing ashore remember to be careful not to place a disposable BBQ where it could set alight wooden jetties, boardwalks, or dry grass and vegetation.BBQs need to be far enough away from the boat so that any hot embers blowing in the wind can’t reach boat furnishings, or any anything else that can burn, like newspapers or clothes.

BBQs need to be far enough away from the boat so that any hot embers blowing in the wind can’t reach boat furnishings, or any anything else that can burn, like newspapers or clothes.When the BBQ is lit, keep a bucket of water or your fire extinguisher nearby.

Don’t forget the carbon monoxide (CO) risk

BBQs continue to produce dangerous amounts of CO for hours after the cooking is over.

It is never safe to have a lit or cooling BBQ in a cabin or covered cockpit area. The only safe charcoal is that which is absolutely stone-cold.

And because of the risk of both fire and CO…

…you cannot drop your guard

Before you dispose of a used charcoal double-check that it is completely cold to the touch, either

Let charcoal burn out and go cold in a safe place protected from wind, or pour water onto the fire.

Used charcoal should be disposed of responsibly.

For more BBQ and outdoor fire safety advice go to the Fire Kills Fire safety leaflets download on Facebook

Boat Safety Scheme

Fire prevention is always your primary protection from fire on boats but a smoke alarm can be your next line of defence, particularly if you sleep aboard. Smoke from a boat fire will affect your ability to breathe, a sensation similar to drowning. With two to three breaths of toxic smoke you could be unconscious. A working smoke alarm of the right type can warn you very quickly of the danger and buy you precious seconds to escape.

Fit alarms and replace them when outdated (check the date label on the alarm).

Never remove batteries and replace the batteries when they have lost power.

Test alarms when returning to the boat, then at least weekly when staying aboard

For more information contact European Marine Services Ltd.  Marine Surveyors & Consultants 
EMS also undertake Boat Safety Inspections & Engine Inspections

www.europeanmarinesurveys.com
Tel: 01603 327 123