#3/ Antifouling. Special Refitting. Time for change. Ten questions in ten episodes.

We continue our journey into the world of refitting, and this time we take the boat… “from underneath” to evaluate together what the alternatives are in the topic of antifouling. Unless you dry-dock the boat frequently, you will not be able to do without giving the hull a good antifouling treatment. And not only because algae and fouling (as a whole, referred to as “biofouling”) reduce a boat’s performance and increase its consumption: in fact, they can progressively affect the structure of the hull by damaging it (e.g., by osmosis phenomena).

3.Antifouling: which one is appropriate for me?

The first question to ask yourself when deciding to re-fouling is, “What kind of expectations do I have from the antifouling I am going to choose?” If what you’re looking for is high performance, because you’re planning a racing season, the advice is to use the hard matrix; if, on the other hand, your use of the boat will be primarily cruising, without the anxiety of tying a few extra tenths of a knot, and you have as your primary need not to have to put your hands on the hull for a long time, then the best choice is the self-sanding. In applications for antifouling you will be confronted with widely varying estimates: some people place the new product on top of the old one without proper sanding, resulting in a crust that will inevitably peel off in four or five years. Instead, before applying the new product, it is essential to sand away the old one and then pass the new one-this way the crust will not form for ten to twelve years. However, it is advisable to cycle the hull to zero, that is, to totally remove all layers of the old antifouling.

Unlessyou dry-dock the boat frequently, you will not be able to do without giving the hull a good antifouling treatment. And not only because algae and fouling (as a whole, referred to as “biofouling”) reduce a boat’s performance and increase its consumption: in fact, they can progressively affect the structure of the hull by damaging it (e.g., by osmosis phenomena).

HOW DO ANTIFOULINGS WORK?
Antifouling paints owe their effectiveness to the presence of biocides (the most widely used is copper oxide; tin has been outlawed for its high polluting power), which are released into the environment in a “controlled” manner so that they are active only in the vicinity of the boat, limiting pollution as much as possible. There are “eco” paints (such as water-based antifoulings, the most famous being Seventy by Veneziani) or innovative ones: some products, for example, contain micro-particles of carbon in such a way as to create an extremely smooth protective film, ideal for racing boats. We will also tell you about paint-free solutions later. Based on their composition, antifoulings are divided into two major families: self-polishing and hard-matrix.

SELF-POLISHING OR HARD MATRIX?
Self-polishing antifoulings (also referred to as water-soluble or self-cleaning), in addition to being chemically active, also count on a “mechanical” effect: this type of paint gradually absorbs water causing a gradual dissolution of the matrix. The chemical action of the water and the mechanical action of the boat’s movement regenerate each coat of antifouling spread (the so-called ablative action). Renewal occurs on the order of microns, so there is no risk of the paint wearing off completely during the season. Self-polishers are not suitable for ultrafast hulls, but they are fine for cruising boats. Moreover, precisely because of the progressive thinning, at the end of the season, once the boat is hauled out, removing the leftover layers with a pressure washer is a breeze.

Hard matrix products, unlike self-polishers, act only chemically. Based on a polymer-type binder (often acrylic or vinyl in nature) they are very resistant to abrasion, so they are an optimal solution for vessels that are winged and carted frequently, or very fast. Generally, they have lower costs than self-sanding paints and suffer less from changes in water conditions (temperature, salinity, currents), so they are also suitable for long-distance boaters. Then there is a third type of varnish, mixed-matrix (or hydrophilic) antifouling, which resists UV rays well and offers excellent flow quality, and is suitable for performance hulls.

EYE FOR METAL
Hulls made of aluminum, steel or iron and generally all metal surfaces require special care, because spreading paints containing metal biocides on them could trigger galvanic corrosion processes that can seriously damage the hull. This is precisely why all antifouling manufacturers offer paint ranges specifically dedicated to the protection of metal hulls, sail drives, bulbs and propellers.

CALCULATE THE RIGHT AMOUNT
To calculate the amount of paintable surface area of the hull we can use this formula: [A x (B+2C)] x 0.4 where A is the waterline length, B the maximum beam and C the draft; 0.4 is the generic hull curvature coefficient for sailboats. Let’s take an example: let’s take a 12-meter cruiser that is widespread in the market, such as the Oceanis 40 (10.35 m at waterline, 4.37 wide and with 1.90 draft). In this case, the paintable area will be 33.8 square meters. Having obtained the value of the paintable surface, we will need to calculate the actual amount of antifouling based on its yield. The yield, on average, is 10 square meters per liter of product (however, it is indicated on each package). Now you will simply divide the area by the yield. Still returning to our Oceanis 40, then, to cover the entire hull with antifouling we will need 3.38 liters. Since the recommended number of coats is two, you will just have to double the result: in this case 6.76 liters (see table for approximate paint quantities based on hull length).

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