Antifouling Your Boat - Why? How? What?

This is all useful Information on antifouling your boat taken from boat painting manuals supplied by Hempel paints, International Paints and Seajet antifouling. Pick up any of these manuals in your local Force 4 Chandlery.

Why Antifoul Your Boat?

"Fouling not only makes a boat look unsightly, it can also foul propellers and outdrives, block engine water inlets and outlets, slow down the boat speed, increase fuel costs and ultimately damage the hull substrate/surface.” - Hempel

They are used on boats to:

• protect the substrate/surface of the hull
• avoids undue hull roughness (roughness increases resistance through the water, causing lower speeds and consuming more fuel.)

Fouling varies widely depending on temperature, salinity and water quality. Differences in levels and types can be dramatic, even on boats moored in what seems to be the environment, as fouling conditions are affected by sunlight/shade, temperature and flow of water, pollution levels and water inflows.

"Fouling grows faster in sunlight, so is first seen on the waterline and rudder. Water surface dirt and pollution can adversely affect the antifouling."

How Antifouling Works

Antifouling paints release bioactive ingredients. The bioactive materials used today are mainly cuprous oxide and booster organic biocides. They're water-soluble and, when released, lethal to fouling organisms.

Different types of antifouling paint release biocides/toxicants in different ways. There are three main types:

• Self polishing / Erodible

Self Polishing Antifouling / Erodible Antifouling - Made using a resin of active ingredients (biocides) repels / discourages fouling. Once in the water, the resin breaks down in a controlled way, continually exposing fresh biocide layers. This gives constant performance throughout the season, and reduces build-up of old antifouling.

• Hard 

The coat's high levels of insoluble resin make it hard and stop erosion. the resin's packed with active ingredients, and the particles are so close that as one dissolves the next is exposed. Hardness and durability makes these antifouls ideal for fast power boats, mud-berthed vessels and racing yachts (burnishing the antifouling with wet abrasive paper before launch gives a smooth finish).

• Traditional / Soft 

A simple resin (gum rosin or rosin derivatives) disperses active ingredients with the binder. Water soluble, it progressively dissolves / erodes, giving low cost protection.

What antifouling should I use?

Cruising motor and sailing boats (max 25 knots)

Self polishing / Erodible

• Controlled release of active substances throughout the season
• Works gradually throughout the season
• Easy maintenance with minimum preperation time
• Launch and re-launch without re-painting

Fast going motor & sailing boats, dry or mudberthed boats and aluminium boats & propellors 

Hard antifoul

• Solid & durable through whole season
• More resistant to polishing and scratching
• Needs to be abraded after the season
• Special products for aluminium made boats 

Racing Motor Boats & Regata Sailing Boats 

Hard antifoul

• For competition & regatas
• smooth hard finish increases speed
• reduces fuel consumption extends motor life
• ensures lower coating thickness.

How much antifouling paint do I need?

As hull designs vary you should only use this illustration as a guide.