Keeping up Appearances - Part Four

At the best of times, painting is one of my least favourite occupations. I find it difficult not to create a mess, particularly with antifouling paint, which I seem to get everywhere.

Painting is not easy, as the boat is generally fairly close to the ground, sitting on blocks under its keel, which necessitates much bending over and reaching for those hard to get at areas.

Someone once said that a successful gardener required a cast-iron back with a hinge in the middle. I've come to the conclusion that this would be an asset to boat painters as well!

PREP FOR SUCCESS
Now, before we look at the subject of antifouling paint more closely, we should review what we have done to the underwater sections of the boat so far.

As soon as the boat was lifted out, the whole bottom was blasted with high pressure water to remove any growth and loose paint.

We then did a thorough inspection, looking for any blistering that may have indicated the presence of osmosis. Repairs were then carried out, and we will imagine that only minor rectification was necessary.

Next we checked all the running gear and renewed any stern and rudder bearings that showed signs of wear, and we also checked the stern gland.

After all that, it might seem as if we are ready to paint the boat and pop it back into the water...

Sorry, there are a few more things that need our attention first.

The underwater fittings that let water into and out of the boat are called skin fittings, and the modern powerboat will have any number of these, depending on the level of equipment onboard.

The largest of these fittings is generally the saltwater inlet for the engine cooling water. These inlets are easily identified and there should be one for each engine.

If the boat has a generator, it will require its own inlet, as will the air-conditioner, the water maker, the refrigerator, if it is water-cooled, and so on.

SKIN FITTINGS
As you can see, a well-equipped boat can have a lot of underwater skin fittings. If any of these should fail, the boat could sink, so we'd best make a thorough inspection of these while on the hardstand. If we do find trouble, it is not all that difficult to replace them, but it is impossible when the boat is in the water.

A skin fitting is almost always made of bronze; there are plastic ones around, but I would not recommend them for below waterline use.

The skin fitting is a threaded tube with a flange at one end. When they are installed, the threaded portion is inserted through a hole in the bottom of the boat. A backing nut is then screwed onto the fitting and done up tightly against a pressure pad.

A ball or gate valve is screwed to the skin fitting. These valves function as a tap and allow the boat owner to close off the water during periods of maintenance.

The skin fitting and ball valve are usually well-made, robust devices that should offer the owner years of trouble free life, but like a lot of things connected with boats, this is sometimes not the case. The most common problem is the ball valve freezing up, meaning that it cannot be shut off in an emergency.

Most ball valves can be dismantled and lubricated to overcome this, and now is the time.

Gate valves have a nasty habit of snapping the shaft that closes the valve, and this generally happens when the valve is closed. Thus, if you are in the water and close the valve for maintenance, snapping the shaft means that the valve cannot be opened again.

This leaves two options: go on the hardstand for a day to replace the valve or change the valve while the boat is in the water - a messy business at best. So the thing to do is to check all those skin fittings and valves while the boat is out of the water.

Open and close each gate valve at least twice and turn the hand wheel firmly home at the fully open and fully closed positions, as this will test the strength of the shaft.

Do the same with ball valves. If they do not operate smoothly, either replace the valves or strip and lubricate them.

ELECTROLYSIS BUSTERS
Now to the most important item of all: the bonding. This is a series of wires that connects together all the metal parts of the boat that are in contact with the saltwater. This is necessary in order to combat electrolysis.

Electrolysis is an extremely complex subject, but basically it means that dissimilar metals in the presence of an electrolyte will attack one another, bringing about metal degradation.

Different metals have different rates of activity and are ranked from the most active to the least. On the average boat many different metals are in contact with saltwater, which is an extremely good electrolyte. Aluminium, brass, cast iron and copper are all found in a common diesel engine's cooling water circuit; bronze skin fittings, stainless steel shafting and stainless steel screws are all found under the water. The combination of different metals and saltwater can be disastrous.

What happens is that one of the metals becomes a cathode and the other an anode. The anode breaks down and the cathode builds up as in electroplating; the result is electrolytic degradation of the metal.

If we take brass, which is an alloy of copper and zinc, and place it in the presence of the electrolyte and the other metals, then the zinc will soon be stripped from the alloy. This leaves a fitting that from the outside looks normal, but will fracture at the slightest knock. For this reason brass should never be used under the water; bronze, an alloy of copper and tin, is much more suitable. (Gate valves are often manufactured in brass, and electrolysis is often the cause of the previously mentioned shaft snapping.)

Luckily there is a simple way to overcome this problem. If a relatively active metal, such as zinc in the form of a large block, is placed in the circuit path of the water and the other metals, and if all are joined together by a bonding wire, the zinc becomes anodic with respect to all other metals. Thus the zinc will slowly erode and protect all the other metals. This is called 'sacrificial protection', and you ignore it at your peril.

Generally the zinc block is attached to the boat by a couple of bolts, often at the bottom of the transom. This is the preferred location, as it makes it possible to renew the block, if necessary, while the boat is in the water. The head of the bolt on the inside of the boat serves as the connection point for the bonding wire, and this wire should spread out through the boat and connect all the metal parts in contact with the saltwater. Note that these are not necessarily below the waterline.

If rubber anti-vibration pads are used in the shaft coupling, they insulate the shaft from the propeller and the propeller shaft. If this is the case, electrolytic degradation of the propeller almost always results, which can bring about the shedding of a blade as the metal fractures - guaranteed to spoil an afternoon's boating, to say the least.

One way to overcome this is to fit a collar anode to the shaft (available at most chandlers in a variety of shaft sizes); the other way is to connect a carbon brush to the bonding bear on the shaft inside the boat. This ensures that the shaft and propeller will be at the same electrical potential as all the other pieces of metal.

Fit a new anode in place of the old one if it is more than 50% eroded.

To test for bonding continuity, use a 12V test light and leads to confirm that there is a circuit between all metal in contact with the water and the anode. Believe me, this will save money in the future.

ANTIFOULING PAINTS
Well, at last all the inspections seem to be complete, and we can think about doing the painting... I can't tell you how much I have been looking forward to this.

For starters, painting with antifouling paint is bound by the same rules as all other painting - if the surface is not prepared properly, the whole exercise is a waste of time and money.

So remove any strainers that may be fitted over the skin fittings. These are attached to the hull by small screws. Clean these thoroughly, as they can suffer from a build up of shell, which reduces waterflow dramatically.

Peer up into the skin fitting itself and make sure it is as clean as a whistle. When doing the painting, make sure the paint goes all the way up into the fittings.

Inspect the painted surface of the hull, looking for any areas which are flaking. All this will have to be sanded back fair and all loose material removed. Wet sanding is best due to the absence of dust.

At this point it might be pertinent to mention that antifouling paints are by nature toxic, so sanding these paints without a good respirator is not clever, nor is working without eye protection. These days I go the whole nine yards: I wear disposable paper overalls with a hood, eye and dust protection and rubber gloves. The decision to do the same is entirely yours.

Clean down the whole hull to make sure all salt and dust is removed from the surface. The propeller can be cleaned using a wire brush, as in all probability there will not be a lot of paint on it anyway - keeping antifouling paints on a propeller is a problem yet to be solved, in my opinion.

You must choose what type of paint to use, although the decision is to some extent determined by the boat itself. If you have any aluminium under the water, only use antifouling paints suitable for that metal.

Refer to the instructions on the can, or contact the manufacturer if in doubt. This is important because the use of a high copper paint on a boat with a sterndrive manufactured in aluminium will result in the aluminium becoming severely eroded due to electrolytic action between these two metals.

A brief word here about antifouling paints and what we are trying to achieve. The object is to produce a coating on the bottom of the boat that will repel or kill living organisms. However, we cannot just use nuclear waste to achieve this, as the environment must be considered. Tin butyl, for instance, although an excellent antifoulant, was found to lead to deformities in marine organisms, particularly oysters. Antifouling must not only be effective, but environmentally sound, too.

Because the ocean is the mother of all life on Earth, the rapidity with which a vessel can foul is astonishing. Barnacles, for example, attach themselves to anything under the water and proceed to feed on the nutrients, while weed comes in many varieties, some of which are difficult to repel from the hull, and slime can foul the waterline with many coatings.

An antifouling paint works by emitting toxins over a period of time, and these toxins deter the growth of the fouling. Unfortunately the playing field is not level and a lot of factors determine the rate at which fouling occurs. Naturally if the nutrient level is high and there is a lot of sunlight, the hull bottom is going to get grubby much faster. Sunlight encourages growth, which explains why the waterline is always the first to exhibit fouling.

SOFT OR HARD?
Manufacturers of antifouling paint have a range of products to suit many applications. For the leisure industry there are basically two different types: soft or hard.

Soft antifouling is of the shedding or ablative types. The surface continually erodes, exposing the toxins underneath until the paint is exhausted. These types are ideal for displacement craft where the water pressure against the hull is low.

For faster boats a harder surface on the paint is desirable, to resist abrasion by the water. These paints have toxins that constantly leach through the paint until they are exhausted.

Both types have their place, but the hard antifouling paints leave a much thicker residual on the hull at the end of their life. Consequently the interval between the removal of the antifouling paint is shorter.

This removal is only necessary when the surface has deteriorated to such an extent that painting over is not possible. Taking off all the old paint, sanding the new surface and applying the primers and undercoats is a task not to be taken on lightly.

A lot of money will be invested in materials as well as labour, so it is imperative that the right information and expertise is sought.

For instance, if using different types and brands of antifouling paint, make sure they are compatible. If you are not sure, ring the manufacturer and follow their advice. But as a rule of thumb, a soft style can be put over a hard, but not vice versa.

Colour does not seem to enhance or detract from the antifouling properties of the paint, although it is a good idea to change every year, as painting a colour over a different colour at least shows the spots you have missed.

Always mask up the waterline with masking tape and paint everything that is under the water, with the exception of the HF radio ground plate. (This is copper anyway and never fouls.)

I like at least two coats around the waterline, but have never found this necessary as I get further down towards the keel. I note where growth has taken place when the boat is first lifted out of the water and make sure those areas have a good, thick covering.

I use a roller and a brush, as being a displacement hull, the finish is not critical. Faster hulls may require the additional cost of spraying.

When the boat is finished, it generally looks so good that I don't want to put it back in the water (like the make-up on an ageing star, the new antifouling paint covers a multitude of sins), but back it must go to start the whole process over again.

I generally manage to get 12 months out of the paint. I don't like to leave it much longer than that because I want to check on the anode and the underwater running gear.

Next month we will be back in the water, but I still have a long list of things that need attention - one day, between all these weeks of maintenance, we might squeeze in a day out on the boat!