How to antifoul your yacht

Yacht ownership brings with it many delights. Unfortunately, the annual anti-fouling regimen is not one of them. 

The need for antifouling paint on your yacht’s hull is self-evident if you take a look at your boat’s bottom at the end of a season, especially if she is kept in warm climes and rarely used. Without regular anti-fouling you’ll start to look like a large plastic jellyfish as you cruise (very slowly) along the coastline.

The art and science of antifouling demands more than one short article, but in an effort to cover the basics, that’s exactly what we’re going to do here.  

Types of Antifoul

The paint you use must be specialist. The environment within it is working is harsh, to say the least, so in our view you are best to go for the best paint you can afford. Then you need to decide what sort of paint to use. There are three basic types;

  • Hard paint
  • Eroding
  • Copper-based

If you can afford it, a copper-based paint should make the ritual of anti-fouling a much less regular affair. Whereas most boats will need treatment annually, a boat painted with a copper-based paint might last for years before needing re-treatment.

If you can’t run to a copper-based solution, there are two other types available to you, namely eroding and hard paint.  The former is the most commonly used and unless your boat is fast (i.e. a race boat or quick cruiser) or sits on a drying mooring, then an eroding paint is probably the most obvious option. Again, in general, the more expensive the paint, the better the solution!

Eroding paint is designed to wear away over time, primarily as the water runs across the hull. The more you use your boat, the more effective it will be - so there’s a good excuse to use when a weekend at the inlaws beckons!

Some race boats might use teflon or other specialist treatments. As you can imagine, this isn’t cheap. It’s also worth mentioning at this point that you need to be very careful when mixing layers of antifoul. Take expert advice.  Certainly, whilst painting and eroding paint over a hard paint might be OK, painting a hard treatment over eroding anti-fouling is not a good idea, unless you want to see chunks of it coming off on the roller - or worse still, once she’s in the water.

If you are in doubt as to what will work best in your area of the world, ask around locally. Local knowledge is worth exploiting.

Preparation for Antifouling

As any decorator will tell you, preparation is everything. Make sure the yard is OK with you working and consider the weather. Antifouling your tub next to a brand new Swan 80 on a windy day might end up being more expensive than you first envisaged! 

Be considerate of your neighbours and clean up after you. Consider putting down ground sheets or, even better, the matting you find in DIY stores for prohibiting weed growth. Water passes through it, but paint flakes will not. At the end of the job, simply collect up the matting and dispose of it. Job done!

Removing old layers of antifouling may not be required. Obviously, if you have many layers, it’s probably time to do a proper job and get right back to the primer or gelcoat, but in many cases this won’t be needed.  However, whether you take it back to the primer or not, you will need to properly prepare the paint surface for the new coat. Make sure the new coat can be used over the old coat, then wet sand the old coat so that it is keyed nicely to accept the new paint. 

If you are taking off the old paint, consider either dry scraping, chemical stripping or soda blasting. This is a messy, time consuming and unpleasant job, so it might be worth considering bringing in a specialist contractor to do this for you. Either way, removing the old antifoul is best done right after she is lifted out at the end of the season, before the surface hardens in the elements.

Apply a primer. You may not have to use a primer if painting straight on top of existing paint, but make sure it is compatible and that the surface is keyed and bubbles and craters are sanded and feathered so that the old paint doesn’t come away underneath the new.

Don’t neglect the propeller and keel. This is an ideal time to sand back the keel’s leading edge, treat for rust and fill any smooth any bumps and cavities. Consider removing the propeller and fairing it ready for it’s antifoul or, better still, send it away to a machine shop to get it polished to a high sheen.

The Antifoul

Antifouling is the easy bit. Remember to properly mix the antifoul in the tins as they will separate over time. Stir them well and then use trays to paint from. Spilling or dropping a whole tin is an expensive mistake to make! Try and choose a dry, warm day and start about mid morning.

Make sure you take your time masking the waterline so that your boot-top line is straight. Mask anything that needs masking and use rollers designed for gloss paint to apply the paint. In my experience, smaller radiator-style rollers work well, but of course the surface area they paint is smaller. Use a pad or brush for the fiddly bits.

Allow the appropriate drying times and for the second coat consider marking the hull with vertical chalk lines. That way, if you paint a section at a time, you have a better chance of making sure you’ve covered the whole hull with two coats.

As the antifoul becomes tacky, remove the masking strips, taking care to dispose of them safely. You don’t want paint-laden paper blowing around the yard.

If possible, once you’ve finished and the paint has dried, get the yard to move your boat slightly in the cradle so that you can treat the area under the pads. Worst case, you might have to do this when she’s in the slings, but you’ll only get one coat on and it’s unlikely it’ll dry in time.

Finally, remember to take advantage of the fact your pride and joy is out of the water and replace the sacrificial anodes.

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