Boats & Bottom Paint: 15 Quick Answers (For Beginners)

Often when boaters gather for cocktails, the conversation drifts to bottom paint.

This is one of the more costly and frustrating items of boat maintenance, but with proper knowledge, the right bottom paint can be found for your boat.

1. What is the Purpose of Bottom Paint?

Bottom paint, often called antifouling paint, is formulated to keep marine growth from forming on the bottom of your hull.

This growth can be stringy or slimy green algae or even hard barnacles attached for the free ride.

All growth causes loss of performance and excess fuel costs, and it looks disgusting!

2. How Does Bottom Paint Work?

Bottom paint contains Copper or Tin compounds that are actually poisonous to marine organisms.

Due to the potential to contaminate waterways, there are now bottom paints without heavy metals that use other chemicals to inhibit marine growth. Tin has now been outlawed in the US and other countries.

That leaves Copper and Copper-free formulas.

3. What Are the Different Types of Bottom Paint?

The two basic categories are ablative and hard bottom paints.

Ablative bottom paints slowly wash away as the boat moves or sits in the water. They act like a slowly melting bar of soap. By ablating, they shed some paint along with marine growth.

These paints also have Copper and other chemicals that inhibit growth. By ablating away, they expose fresh layers of paint with fresh chemical compounds.

Do some research among paint manufacturers; there are hard and soft ablative paints.

The soft is more effective in inhibiting growth but doesn’t last as long as harder compounds.

Ablative Paints Are:

  • Easy to apply by roller, even over older ablative bottom paint that has been thoroughly cleaned.
  • Cost is slightly lower than hard paints.
  • The hull bottom stays clean without scrubbing, as long as the paint is not used up.
  • It can wash away too quickly, requiring more paint to remain effective.
  • They are usually thick and do not provide a slick, smooth hull finish.

Hard bottom paints contain Copper compounds like ablative paints but are thinner, longer-lasting paints. They are designed to be effective for several years and not wear away as quickly.

Hard Paints Are:

  • More demanding of surface preparation. All old paint, especially ablative paint, must be removed.
  • Require scrubbing, about once/month, to remove marine growth and expose more chemical compounds.
  • More costly to buy and apply than ablative paints.
  • Provide a smoother, slicker bottom finish for higher performance.

4. What’s the Best Bottom Paint?

That’s a favorite topic in sailor’s bars.

There is no simple answer but let’s look at some guidelines:

Most Important: What’s Under your Bottom Paint?

Fiberglass boats have an outer surface of tough gelcoat.

This is sprayed in the mold before laying up the fiberglass. Gelcoat does absorb a small amount of water.

Therefore, multiple coats are necessary for a water barrier between you and the gelcoat. A good practice is to alternate the coats with gray and white 2000e so you can see in the future how far you have sanded through your barrier coat.

The barrier coat must be sanded before applying bottom paint to have proper adhesion. A sanded barrier coat is the perfect primer for any bottom paint.

Watch Out for Blistering:

Older boats and some newer ones suffer from osmotic blistering of the gelcoat.

This occurs when water absorbs through the gelcoat into the first layers of fiberglass. The water can actually build up pressure that pops the gelcoat up like a blister.

Any boat that has osmotic blistering requires serious, remedial work.

The blisters must be removed by grinding or sandblasting. After the hull is completely dry, the blisters are filled with an epoxy filler and sanded smooth.

To prevent future blistering, layers of epoxy barrier coat must be applied. Interlux 2000e works well.

Fresh Water Boats Have Limited Choices for Bottom Paint:

One choice instead of using bottom paint is to use a boat lift or dry storage.

If not, Interlux VC17 and Petit SR21 work fairly well and are easy to apply.

  • They are skinny, so they tend to give a smooth finish.
  • They require scrubbing every month, more frequently for racing boats.

Ablative bottom paints work fairly well, too. If they don’t effectively inhibit growth, they will ablate off to remove the growth along with a fraction of the paint.

Salt Water Presents More Challenges:

There is a greater variety of organisms in saltwater that like to hitchhike on your hull.

Warmer water temperatures also accelerate growth.

  1. Talk with other boaters in your area. Find out what works best.
  2. Consider how often you will pull your boat out of the water for cleaning or repainting.
  3. Consider the added expense of hard paint if you can easily snorkel or dive to clean your boat bottom.

5. Can I Apply my Own Bottom Paint?

Most paints have explicit instructions for the DIY boater.

As always, follow the manufacturer’s instructions, but here are valuable tips on a successful bottom job:

  1. Clean and sand the bottom, so there is no loose paint or debris.
    • All bottom paints require a sound base to adhere to.
  2. Assemble all supplies, thinners, rollers, protective clothing you need and buy extras.
    • You don’t want delays in your project.
  3. Stir the paint well!
    • There are a lot of solids that need to be dispersed in the paint.
  4. Watch the weather.
    • Temperature and humidity must be within the manufacturer’s specifications. Of course, rain can make a mess of a bottom job.
  5. Allow thorough drying between coats.
    • Applying thick coats in succession can entrap solvents and cause the paint to remain soft.
  6. Allow extra time after the final coat before launching.
    • There is nothing worse than a perfect bottom finish marred by lift slings or trailer pads.
  7. Be patient!
    • Plan on a week to clean, sand, and apply bottom paint.

6. What Colors are Available in Bottom Paint?

In years past, bottom paint was dull, red copper color.

Now the manufacturers add a variety of tints. Some are quite vivid (Micron Vivid), but most turn a dull color when exposed to water.

All look bad when covered with marine growth, but black seems to hide the appearance of marine growth the best.

7. How About Bottom Paint Safety?

Bottom paints contain chemicals poisonous to marine growth.

They are also toxic to humans and animals.

Sanding old bottom paint is especially dangerous. Wear protective clothing and breathing devices!

There are often environmental regulations regarding sanding, washing, and applying bottom paint. Ask at your boatyard to be sure you comply.

We do not want to pollute the beautiful waters we enjoy on our boats.

8. How Much Bottom Paint will I Need?

Manufacturer’s websites help estimate how much you should buy.

Be aware that some paints have a shelf life. Don’t buy extra that might expire before you re-paint.

We used four quarts of VC17 or SR21 on our 28-foot sailboat in Lake Michigan. We now live aboard a 42-foot sailboat and use four gallons to re-paint.

9. How Long will the Bottom Paint Last?

The goal for most boats that stay in the water year-round is two years.

Our experience is that performance is poor during the second year; we have to do a lot of scrubbing. Boats that are used during only a summer season can often go two years on a bottom job. Some routinely put on a fresh coat every year.

Some hard bottom paints like Coppercoat can last 10 years. This is a highly specialized, epoxy/copper paint that must be applied with care. I saw a boat out of the water that sailed with Coppercoat for two years, and the bottom looked like new.

The owner said they do have to clean the bottom every month, though.

Petit Trinidad SR can last several years but, again, needs monthly scrubbing.

10. What’s New in Bottom Paint?

Copper-free bottom paints have emerged on the market to be more friendly to the environment.

Some contain non-metallic biocides. One unique paint is Epaint, EP 2000. This water-based paint forms a layer of Ozone when in the water. This Ozone is toxic to all marine growth but has no lasting pollutants.

We used it on the keel and rudder of a racing boat, and it stayed immaculate all summer.

It just rolled on like house paint. However, it wasn’t easy to sand to a smooth, racing finish.

11. What’s the Best Bottom Paint for Speed?

The simple answer is “none” because your boat’s factory gelcoat finish is probably smoother than any bottom paint.

If racing performance is the goal, wet sand the gelcoat and keeps cleaning the bottom or hauling between races. We did this for years with our 28-foot race boat, Veloce. We would haul the boat on the yacht club crane and scrub before every race.

It took only ½ hour, and we always had the confidence of a perfect bottom.

For boats that must have an antifouling paint, hard paints are the fastest.

They can be wet sanded to be almost as smooth as gelcoat. Ablative paints, sloppily applied, look like roofing tar. But if applied with care, it can provide a smooth finish.

Remember, any marine growth will be slow, regardless of the type of paint. Antifouling paint will help with boat speed and fuel savings.

12. How Much Does it Cost to Have the Boat Professionally Painted?

There are a lot of factors involved in the cost.

Bottom cleaning and sanding, type of paint, cost to haul and launch the boat, and boat size contribute to cost.

As a rough average, bottom jobs can cost from $20/lineal foot to over $100/lineal foot. We do most of our own work on Uproar, our 42-foot sailboat, but we have had quotes as high as $5,000 for the entire project!

We do our own painting on Uproar. The cost of hauling, bottom washing, bottom sanding, a week in the yard, and relaunching is under $2,000.

The cost of paint is usually $600. By applying the paint ourselves, we save a lot.

13. Are There Special Concerns for Aluminum or Steel Boats?

Yes, any two different metals can cause corrosion.

Proper epoxy barrier coats can prevent the problem, but the manufacturer’s specifications must be followed.

The new, copper-free paints are ideal for Aluminum or Steel hulls.

14. Is There a Bottom Paint for Pontoon Boats?

Epaint even makes a special formula for aluminum pontoon boats.

They also make paint for inflatable dinghies.

15. Where Do I Start?

Talk with other boaters in your location.

Talk with boatyards and charter fleets. You will get a variety of opinions but can determine what would work best for your boat.

If you plan to start living aboard your boat, raise the waterline and paint higher on your hull. Your additional cargo will sink your boat deeper in the water.

Plan your project. Assemble all materials, tools, and protective safety clothing. Prepare a workspace where you won’t accidentally paint your friend’s BMW (ask me how I know). Get help from friends who boat with you.

Wait for the proper weather and be sure to allow proper drying time.

No matter how well you apply your bottom paint, plan on some periodic hull cleaning. This is one project that, if left too long, becomes a nightmare of barnacles and algae.

A clean bottom is essential for boat performance and getting the most enjoyment out of your boating lifestyle.

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