The Lowdown On Bottom Paint

By Frank Lanier

While death and taxes may be better known, there's a third certainty in life many boat owners face that's often viewed with just as much trepidation.

Photo of painting boat bottom with small roller
Photo: Billy Black
Bottom paint is a "must have" for boats that spend most of the year in the water.

Hybrid or semi-hard ablative paints bridge the gap between ablative and hard paints by incorporating the benefits of both into a single product. They provide a hard, smooth surface that resists buildup yet holds up to faster speeds and repeated haul-outs without loss of protection.

The type of boat you have plays a significant role in bottom-paint selection. Highspeed powerboats will want to use a hard or possibly hybrid bottom paint — ablative paints simply won't last as long at speed. Trailerable boats are best off without bottom paint, but if that's not an option, consider a hybrid paint, which will hold up better throughout the constant launch and haul-out cycles (most hard paints can't tolerate being out of the water for extended lengths of time). Slower craft can use hard, hybrid, or ablative type paints, but the benefits of the latter two (no buildup, self-cleaning, etc.) should be considered when choosing. (For an indepth review of bottom paints and long-term test results, see Practical Sailor magazine:

Application Considerations

For boats not currently painted, application is simply a matter of following the paint manufacturer's instructions for application to a new or unpainted hull. If your boat is currently painted, you have a few considerations to address before repainting. Not all bottom paint types are compatible, so unless you plan on removing ALL of the existing bottom paint, the paint you currently have will influence your choice of new paint. If you know the brand/type of bottom paint on your boat now, the options are straightforward — either continue to use the same paint or (if using a different paint) consult manufacturer specs for both paints (old and new) to ensure compatibility.

If you don't know who the manufacturer of your current paint is and plan on painting over it, at a minimum you'll need to determine whether it's a hard, semi-hard, or ablative type. One straightforward way to do this is by rubbing the existing bottom paint with a wet rag. If the paint readily rubs off, it's most likely ablative. The general rule is that ablative paints can be applied over properly prepared hard or semi-hard paints, but hard or semi-hard paints can't be applied over ablative paints (which wouldn't provide a proper adhesive surface for the hard paint). For those wanting to switch from soft to hard paint, the ablative paint would need to be removed first.

Depending on the paint and its condition (i.e. good adhesion, no flaking, etc.), proper surface preparation of your old paint can range from a light sanding to complete removal or application of a primer coat. New paint adhesion will only be as good as the paint beneath it, meaning paint in poor condition or showing signs of significant adhesion failure must be removed. Err on the side of removing more paint rather than less, but beware: If your boat has a barrier coat applied, make sure your methodof bottom paint removal doesn't damage or remove it along with the old paint.

Choosing A Paint

Tip iconAlternating ablative bottom paint colors (first coat red, second coat blue, for example) gives a visual cue as to when your paint needs renewing.

As you can tell by the sheer number of bottom paints on the market, no one type or brand works best in all water, weather, and locations. A boat moored in Maryland will require a different antifouling paint from one cruising tropical waters. One of the best sources of information on which paints work best for a particular area is your local boatyard manager. Fellow boat owners can also provide valuable local knowledge regarding which paints work best in your location. Finally, many bottom paint manufacturers such as Interlux ( and Pettit ( offer online charts and tables to assist in choosing the right antifouling paint for you boat and location.

While there are plenty of bottom paints to choose from, there's no magic bullet that stops growth altogether. Boats kept in the water year round or for the season will still require regular cleaning and periodic hauling for repainting. In northern climes where boats are hauled annually, bottom jobs are usually rolled in with the other spring launch preparation rituals. Bottom job schedules for other locations vary, but are typically required every two to three years.End of story marker

Frank Lanier is a marine surveyor with over 30 years of experience in the marine and diving industry. He holds a 100GT master's license, and has captained and maintained many different types of vessels.

Published: April/May 2014


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Rejuvenating Hard or Semi-Hard Bottom Paints

Refer to manufacturer instructions for your specific paint, but the following are general guidelines for launching and relaunching of vessels with hard or semi-hard (modified) paints applied.

  • Newly painted boats — Launch delays of up to 60 days after painting with no loss of performance or special requirements necessary
  • Boats launched two to 12 months after painting — Scuff-sand with abrasive pad or 220-grit sandpaper prior to launch
  • Boats launched more than 12 months after painting — Light sanding with 100-grit sandpaper followed by recoating


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