What is Antifouling?

Antifouling is a protective coating that is applied to the hull of a boat from the waterline down. Its purpose is to prevent osmosis which is simply the process of water slowly penetrating the hull, in exactly the same way as your fingers getting wrinkly in the bath.

Marine Scaling Build Up on This Hull With No Antifoul – We Recommended A First Antifoul Treatment as She Was Going to be Berthed on a River

If osmosis is allowed to happen it causes blistering of the gelcoat which means it is no longer fully protecting the fibreglass below it. This will then lead to water penetrating the fibreglass and into the boat which ultimately can sink your boat. Besides the obvious danger of this happening with people aboard, the cost of any repairs to the hull once osmosis is allowed to start can easily run into the tens of thousands.

So if your boat will be kept in the water for any more than a few days on a regular basis, it is advisable to protect the boat and yourself from huge potential repair bills by having the hull antifouled.

What Does Antifouling a Boat Involve?

There are really 2 types of conventional antifoul:

Erodible antifoul is best suited for slow moving vessels like yachts or motor boats cruising below 20 knots. We use International Cruiser Uno which is applied in one thick coat once a year and gently erodes throughout the course of the year, protecting the hull from osmosis and preventing excessive build-up of organic material under the boat.

Hard antifoul is designed for boats that cruise above 20 knots as erodible is not durable enough to last a whole season under these conditions. We use International Interspeed Ultra which is applied in 2 coats and is designed to provide the same protection from osmosis, but prevents marine fouling build up by creating a surface that is more difficult for organic material to attach to.

Because No Antifoul Had Been Applied a Thorough and Detailed Preparation Was Needed

Can I Antifoul My Boat Myself?

Many people do their own antifouling because applying it is effectively the same as painting and for the same reason it is a common service offered by many marine businesses. There are 2 elements to antifouling boats; preparation and application, both of which are equally important to make sure the hull of the boat is properly protected for the year.

If your boat is new or has never been antifouled before, it is ESSENTIAL to have the correct preparation and priming of the surface done before applying the antifoul. Over 95% of boats we look at have not been prepared properly before their first antifoul and the consequences are:

  • A flaky hull needing much more preparation before antifouling again – Cost in additional preparation time
  • Patches of filling needed to be done on the flaky areas to prevent osmosis setting in – Cost of professional repairs
  • Vulnerability of the flaky / thinly protected areas of hull allowing osmosis to set in – Huge repair cost

Each of these painful outcomes is a very common but unnecessary occurrence because it can be easily avoided if the first antifouling is done correctly. I’d like to explain exactly what is needed to avoid this yourself

How to do a Boat’s First Antifoul to Avoid Future Hull Repairs

Regardless of who carries out the work for you, its very important that the hull is prepared properly before anti fouling for the first time. Osmosis, as you are now aware, is the process of water penetrating the hull’s gelcoat and will eventually compromises its integrity which can lead to massive repair costs (if it can be repaired at all).

The following work must be carried out to ensure you give the peace of mind of the best lasting protection to the boat:

Keying the hull before Priming

It is essential that the hull is keyed (roughened) properly or the primer and antifoul will peel and flake off. Most companies use a scouring pad to do this very quickly and we see the detrimental effects in most hulls we look at because it simple does not create a surface that the primer can really grip hold of.

Methoical Detailed Sanding Without Damaging the Hull’s Gelcoat Surface

We use detail sanders over the entire hull, working very delicately to ensure the gelcoat is not damaged. The tidiness of the edge of the antifoul at the waterline has a big effect on the boat’s presentation in the water, especially if it starts to peel because it hasn’t been done properly. Look at most other boats and you will see examples of the overall effect on a boats appearance with an untidy or flaky waterline.

A Perfectly Keyed Hull Ready For Priming with International Primocon

Priming the hull before First Antifouling

Two coats of primer are needed. These form the primary base layer of protection to the hull and make the antifoul stick to the hull much more effectively. Some companies do not prime at all and again there are the same long term risks of big repair bills if it isn’t done.

The First Primer Coat being applied

Careful Masking Is Well Worth While to Create a Neat Waterline that Wont Flake

Also bear in mind that each year when she is antifouled this primer layer forms the base of every coat of antifoul she receives so you can understand the importance of it being applied in 2 thick even layers and that the hull’s gelcoat beneath is keyed thoroughly so this base coat can do its job for many years.

The Primed Hull Ready to Antifoul

Applying the Antifoul

Depending on whether you have a boat that cruises above or below 20 knots, a hard antifoul or an erodible one should be used respectively. There are many antifouling paints; if applying a hard antifoul we use International Interspeed Ultra which is a good quality antifoul and we apply 2 coats, with an extra thick coat on all leading edges and at the waterline where the vessel experiences most drag from the water. If applying an erodible antifoul we International Cruiser Uno in an even thick layer, with an extra thick layer at leading edges and along the waterline for extra protection.

Antifouling Being Applied – Detailed Areas Left for A Detai Brush

Its worth mentioning that the first time it is done there is much greater attention to detail needed to firstly make sure the antifoul is applied thoroughly and secondly because it affects how the boat looks over its life; future antifouling will just follow the lines of the first antifouling so its important that it looks right. Carefully masking up the waterline for the first time is something we place great importance upon and the results make it well worth it.

Completed Antifouling Ready for The Unmasking Before it Dries

Annual Re-Antifouling

After 12 months in the water the boat should be lifted out for re-antifouling. Again many people will do this themselves and its a much more straightforward job than the first antifouling coating, especially if it was done correctly the first time.

The preparation is, once again, the most important part and the entire hull must be completely de-scaled with a pressure washer and by hand. Any fouling that is not completely removed will not provide the antifoul with the surface it needs to grip onto all season long which means the hull will be vulnerable to osmosis in those areas. Again, someone will have to spend a lot of additional time or money on preparing areas that have not been fully descaled and the antifoul is flaking away around them, before re-antifouling.

Masking up the waterline is much more simple as there is an existing line to follow and applying the antifouling paint should be done thoroughly, with an additional or thicker layer at the waterline and on all leading edges of the hull.

Outdrive Painting and Stern Gear Polishing

As part of a thorough protection of a boat below the waterline the outdrives should be painted with a protective marine paint to minimise marine fouling build-up which can impede the mechanics of the equipment and affect running efficiency.

For yachts and boats without outdrives the stern gear should also be polished for the same reasons. The anodes should be checked and replaced if they are getting low. Both of these services are offered as part of our complete antifouling service.

Machine Wire Brushed Running Gear – An Optional Part of Our Antifouling Service

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