Bottom paint for your yacht—the right way

Painting the bottom of your yacht isn't as sexy as installing a brand new electronic navigation systems with all sorts of great bells and whistles—but it is an important part of protecting your hull and ensuring a long service life for your vessel. So I'd like to take moment to talk about what we look for when evaluating a bottom, our process for preparing and then painting the bottom, and about the different kinds of bottom paint available for your yacht.

Evaluating the bottom

First, let's talk about what we see when the boat has been lifted out of the water and cleaned with a thorough power washing. We check for lots of things that we're able to see right away, including: unusual wear or damage and the condition of the cutlass bearings, zincs, propellers, thrusters, rudders and trim tabs.

We then consider the following questions:

Is there obvious electrolysis?
Electrolysis is the result of stray electrical current in the water. The zincs are there to protect your boat against electrolysis, but if there's enough current, sometimes the zincs can't keep up with it. 

Severe electrolysis on the transom of a power yacht.

Severe electrolysis has destroyed this propeller blade.

Electrolysis can range from minor to severe - these images are taken of a severe case. On the transom around the zincs, all of the bottom paint and even the gelcoat has decomposed leaving bare fiberglass visible. The propellor is so severely pitted that there are pinholes on the edges. 

This boat's bottom is in the process of being treated for blisters. Here, the bad areas have been ground out and are drying before being patched, sealed and finished.

Are there blisters?
When your boat is hauled for a survey, and the surveyor starts banging away on the bottom with a hammer, one of the things they are looking for is delamination. Blisters are a kind of delamination, area in the hull where water has penetrated beneath the gelcoat and gotten into the fiberglass. When the surveyor taps a blister with a hammer, a blister makes a different sound than the rest of the hull. Most blisters show up on the bottom as pronounced bumps of various size. Not all boats suffer from hull blisters, but if yours does, it's a good idea to take care of them while the boat is out of the water for bottom paint.

The bottom paint here is too thick and falling off.

The bottom paint here has worn through to the primer.

How much bottom paint is already on the boat?
When we sand the bottom, how much sanding is to be done depends in part on how much paint is on the boat. If there is too much paint, it's important to sand off the excess. If the paint is too thick and starting to chip and flake, the new paint will fall away as the old paint underneath it fails. We sand the bottom so there is an optimal thickness of paint remaining, allowing for a strong bond between the new paint and the hull.
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Too little paint can also be a problem. If the gelcoat is visible through the paint, or if there is too little paint for us to sand without scratching the gelcoat, we'll need to apply a barrier coat of epoxy to protect the gelcoat and the fiberglass.

Is the bottom paint falling off the bottom?
Needless to say, if the bottom paint is falling off the bottom we need to remove all of the loose paint—and all of the paint in danger of becoming loose—before adding new paint. There's no point in spending money on new paint if it's just going to flake off when the old paint gives way.

Planning your bottom job

Once we've identified any potential problems with the bottom paint that need to be addressed, we'll discuss a plan for sanding, preparing, and applying bottom paint. It's important to realize that this plan is customized to your boat, its condition, and where it will be going: there is not one bottom paint or one standard treatment that works for all bottoms.

Choosing your bottom paint

The first question we ask is what kind of paint the bottom has on it. There are two main categories: hard and ablative (semi-ablative paint combines the qualities of the two). Here's a quick comparison between the two:

TYPE OF PAINT:	HARD PAINT	ABLATIVE PAINT
How does it work?	Hard paint keeps growth off your bottom with a biocide in the paint.	Ablative paint works by ablating, or sloughing off small quantities of paint as growth attaches to it. ​
When is it time for new paint?	​When the biocide stops working, and barnacles start to stick, it's time for new bottom paint.	​When the paint gets too thin, and you can start to see the primer underneath the paint when cleaning the bottom, it's time for new bottom paint.
​How much paint do you need?	One coat of hard paint, with an additional coat at the waterline is usually sufficient.	Because the paint ablates, 2-3 coats will build up the thickness of your paint film and lengthen your bottom job's service life.
Why choose this kind of paint?	If you have a diver cleaning your bottom, we recommend a hard paint because it stands up to regular cleaning. Hard paints require fewer coats and last as long as the biocide is potent.	If you're moving your boat frequently or you don't have a diver, an ablative paint is a good choice. Movement of water over the paint will help keep the bottom clean. Because the paint ablates, there's also less need for sanding.
Common brands:	Pettit Trinidad	Sea Hawk Biocop (ablative) Cukote (semi- ablative)

We can usually tell whether your old bottom paint is hard or ablative, and plan accordingly. Ablative paint can go over hard paint, but hard paint can't go over ablative paint. It's helpful to know what kind of bottom paint is on the boat so that we can prepare the bottom according to the manufacturer's recommendations.

​Another factor that we consider when recommending a bottom paint is where the boat will be moored. Different paints perform better in salt, brackish or fresh water, and water temperature affects how much growth you'll be combating. We base bottom paint recommendations on our knowledge of the area and the challenges posed by different locations.

Sanding, epoxy barrier coats, and blister repair

The biggest variable in the cost of a bottom job is the preparation time. Depending on what kind of paint you choose and the condition of your bottom, we will make a plan for sanding and preparing your bottom. This typically falls into one of three categories:

Light sanding
If your bottom paint is in good condition, the paint isn't too thick and we're applying the same or similar paint over your old paint, a light sand may be all you need to prepare the bottom. 

Hard sanding
If you have a thick buildup of paint or if there are areas where the paint is falling off, you may need a hard sanding. This takes more time, but it returns the bottom to a new starting point for the paint, which will result in easier bottom jobs in the years to come. Hard sanding takes the paint down to a thin base so we can start fresh with new paint.

Hard sanding with and epoxy barrier coat
If we have to take the paint all the way to the gelcoat, due to the condition of the paint or other problems with the hull like blisters, we have to remove all of the paint from the bottom. We then follow this with a multiple layer barrier coat of epoxy to seal the gelcoat and protect the fiberglass, which is then painted.

A note on blister repair
If your boat has blisters, there is a process we go through to grind out the blisters, let them dry out, and then fill and seal the fiberglass to protect the integrity of the hull. 

Getting your boat back in the water

Once we've arrived at a plan for the boat, our team gets to work sanding and preparing the bottom to receive the new bottom paint. Here at Snead Island, we take the time to sand the bottom thoroughly, clean the metal, sandblast the sea scoops, and remove and clean bow and stern thruster propellors. It takes time to do a quality job, and we pride ourselves in doing the job well.

Sanding the bottom.

Cleaning the prop, strut, shaft and other metal.

Rolling on bottom paint.

Typically we complete bottom jobs in five to seven working days, though it can take longer for larger boats or to address more severe problems like blisters, damage or electrolysis. ​