Make sure your hull is clean and ALL traces of grease and marine growth have been removed, if necessary wash the hull with a detergent or a degreaser so as to remove any contaminants. If you have any stubborn remnants of barnacles – or the white calcium deposit left after pressure washing they can be easily removed using Boat Bottom Cleanerhowever make sure you wear gloves and eye protection when using this product as it is quite aggressive.
Lightly abrade the old antifouling with 120 grit paper preferably used wet, make sure you wear a mask, gloves and eye protection; antifouling not only kills marine growth, any dust produced can create severe respiratory problems and irritation to humans. After rubbing down make sure all the slurry is washed off with fresh water. No doubt the poor weather over the last few weeks has delayed your antifouling however don’t be tempted to apply primer, antifouling etc when the substrate is not free of moisture!
If you are changing to a different make/type of antifouling make sure it is compatible with the one you are covering, if not, or if you’re unsure of the existing antifouling, apply an appropriate barrier coat such as Seajet Underwater Primer or one recommended by your chosen antifouling manufacturer. All loose antifouling must be removed, if it is just small patches you should be able to feather the edges of the patches using your 120 grit so the area will not show through the new coating, patch coat these areas with the barrier coat followed by antifouling before giving the full hull a coating. If you have a build up of a number of seasons applications of antifouling you should perhaps consider removing these. Not a pleasant job but worthwhile as it will save you future problems! This can be done by just using a scraper, although it is often easier to use one of the gelcoat friendly antifouling removers or Peelaway – don’t be tempted to use standard paint removers as this may adversely affect your hulls gelcoat. Be careful not to damage any underlying epoxy coatings, when you have removed the old antifouling if your hull hasn’t had a protective coating of epoxy it may well be worthwhile coating with Seajet 117 Multipurpose Epoxy Primer to give protection against osmosis, however you must abide by the manufacturer’s instructions regarding temperature, mixing, application and over-coating materials.
Iron keels should be rust free, in an ideal world shot blasting and coating with several coats of Interprotect or the likes will give long lasting protection, if you have a Westerly with rusted keels (bilge or fin) it would be advisable to Tercoo blast or shot blast clean then leave as long as possible before sweep blasting again removing the surface rust before priming – Westerly keels are notorious for being porous and retaining water, shot blasting and immediately painting usually results in failure of the paint system owing to moisture retention in the steel under the old coating.
If you are unable to shot blast, grinding clean and coating with 4-5 coats International Primocon (first coat thinned) or similar will give good protection, observe the recommended over coating times for various antifouling types.
Alloy Hulls, Outdrives etc:
If you have just purchased an alloy boat please note you must NOT use an antifouling containing copper, likewise alloy outdrives and outboard legs. Use something like International’s Trilux or the like and remember if antifouling a GRP hull fitted with outdrive(s) or outboards and it’s a copper based product that you are going to apply, it is recommended that you leave at least a 25mm gap around the unit.
If you have to fill any underwater surfaces as a result of hitting an underwater object or over enthusiastic use of a scraper, do not under any circumstances use a polyester filler, use only an epoxy based one such as Epifanes Epoxy Filler 1500.
When masking water lines make sure you use the ‘Blue’ 14 day tape product which not only gives a good crisp line but can also be easily removed on completion of the paint job. If you use standard paper masking tape ensure you remove it immediately you have finished painting; However if you have had the misfortune to leave this style of tape in place and find it impossible to remove, 3M Citrus Cleaner is an excellent product to assist, WD40 is also worth a try.
Wear disposable gloves and eye protection when applying antifouling as splashes on hands and face irritate the skin and using thinners to remove them can make it worse by driving the material into the pores making it difficult if not impossible to remove.
Apply the correct number of coats of antifouling as recommended by the manufacturer – usually a minimum of two, on high pressure areas on your hull (leading edge of keel, rudder etc) they can benefit with the addition of a patch coat before painting the whole hull. Do not be tempted to thin the antifouling, you are diluting the active ingredient! Use a roller as it will give a better coverage and finish than using a brush, if using a plastic paint tray place it / cover it in a plastic carrier bag before use, not only will you be able to use it again, many solvents in antifouling melt plastic paint trays leaving you with a sticky mess to roll onto your hull!
Do not paint over your transducer with conventional antifouling, use a water based antifouling as this will not damage the transducer surface nor weaken the signal!
Specific Boot topping paints such as International ‘Trilux’ or Hempel Waterline Boot Top perform better than standard antifouling as they tend to be of the ‘hard’ type, are stronger and will stand up to the occasional scrub during the season.
Propellers should be cleaned and polished with fine emery cloth or wet and dry. If you are in a heavy fouling area coat with Sea Jet Peller Clean or International ‘Prop-o-Drev’ this will help keep the prop clean whilst a coating of Propshield will be of benefit in lesser fouling areas. Dispose of masking tape, rollers and safety wear responsibly when you’ve finished.
Anodes, remove if possible before antifouling, if there is still 2/3rds left and you’re leaving them in situ, either mask off or coat with soap before you start work, antifouling on the anode surface will prevent it working!