Painting a boat isn’t just about aesthetics. Sure, giving your boat a new lick of paint helps to keep the boat looking fresh and new, but paint actually serves a purpose.
This means that while the bottom of the boat is almost never seen by other people when it’s underwater, it still deserves paint as a layer of protection.
However, you can’t just use any old paint to paint the bottom of your boat. The material of the boat will determine the type of paint you use. Plus, the bottom of a boat is likely to experience the most abuse from scratches, constant exposure to water, and marine growth that can slow your boat down.
Here is everything you need to know about how to paint the bottom of your aluminum boat!
Should I Paint The Bottom Of My Aluminum Boat?
To put it simply – yes, you should paint the bottom of your aluminum boat. Without a layer of protective paint, your boat is more likely to develop marine growth such as barnacles and algae.
While this might not seem like an issue, marine growth can actually exhaust your boat, because the presence will slow the boat down in the water and therefore force the engine to work even harder. The harder your engine works, the more expensive fuel is going to cost.
Sure, spending a little more money on fuel might not sound like a bad thing, but marine growth at the bottom of a boat has the potential to be quite dangerous.
Algae, barnacles, weeds, and slime act as another barrier to push through the water, rendering the streamlined shape of the boat virtually useless. This means that marine growth will affect your boat’s ability to maneuver, which can result in accidental crashes against other boats or objects in the water.
While small barnacles and algae might not seem like a huge problem, you’ve got to think of marine growth like mold. It starts off in small patches, and eventually grows to infect the whole of the bottom of the boat. Without persistent care, the growth can be a nightmare to clean and cure in the long run.
However – there is one exception to this rule. You probably won’t have to paint the bottom of your aluminum boat if you regularly pull the boat out of the water, because this will prevent marine growth from occurring.
If you keep your boat in the water after every use – particularly if it remains stagnant in the harbor – then it will require a layer of protective paint to prevent marine growth.
What Paint Should I Use On The Bottom Of An Aluminum Boat?
To paint the bottom of an aluminum boat, you will need to use antifouling paint. Antifouling paint prevents the growth of marine organisms due to a biocide ingredient in the paint, which works to stop slime, weeds, algae, and barnacles from attaching to the bottom of the boat.
There are several types of antifouling paint available, with each type designed to work with a particular boat material or type of water.
Ablative Bottom Paint
Probably the most common type of antifouling paint, ablative bottom paint is a soft paint that gradually wears off over time due to the water from waves and currents. As each layer washes away, fresh biocides are released to prevent barnacles and algae from adhering to the surface.
Because ablative bottom paint needs to wear off for the biocides to be most effective, this paint type is best suited for boats that are used regularly. Just make sure you pick a paint suitable for either multi-season or single-season use depending on your needs.
Hard Bottom Paint
Unlike ablative bottom paint, hard bottom paint doesn’t wear down over time. This means that the biocides are constantly exposed to prevent marine growth from attaching to the surface.
As a result of this, the paint becomes ineffective once the biocides have been released, so it will need to be sanded down and reapplied in time for the next season.
Hard bottom paint is essentially useless when the boat is lifted out of the water, which is why this paint is best suited for boats that remain in the water for long periods.
Self-polishing Copolymer Ablative Bottom Paint
Self-polishing copolymer ablative bottom paint also wears off over time like ablative bottom paint, but this paint is suitable for boats that are both used frequently or not.
This is because the paint is self-polishing, which is when the copper copolymer is released in a controlled way to prevent the paint from wearing off when the boat is out of the water, which would otherwise render the paint ineffective.
Hybrid Copolymer Ablative Paint
As the name suggests, hybrid copolymer ablative paints are a mix between all three of the above paint types! This paint type releases biocides at a controlled rate like self-polishing copolymer ablative paints, but they can also be polished by rubbing like with hard bottom paints.
However, these paints are easier to remove and reapply than hard bottom paints.
How To Paint Bottom Of Aluminum Boat
Step One: Prepare The Surface
Turn the boat over so the bottom is facing upwards. Wash the bottom of the boat with a pressure washer, and then scrub away any lingering debris or dirt. This is to ensure that the surface is entirely flat and will allow the paint to adhere to the surface evenly.
Then, allow the surface to dry completely and apply a water-tight barrier. You might need to apply more than one surface for maximum adhesion.
Step Two: Apply The Paint
Once you have chosen the appropriate antifouling paint for your boat, you can then apply it with a spray gun. A spray gun works similarly to a pressure washer in that it applies an even layer of paint to the surface of the boat. Plus, it takes way less time than using a paint brush.
However, you can also use a brush or roller if that is all you have access to. Allow enough time for the paint to dry before applying another layer if needed.
How To Reapply Antifouling Paint
Reapplying antifouling paint is very similar to applying antifouling paint in the first place. You will need to use a pressure washer and sand the surface to remove the original paint.
If you apply a new layer of paint directly onto the surface without removing the old paint, parts of the bottom of the boat will be more exposed to developing marine growth than others.
Frequently Asked Questions
Do Aluminum Boats Need Bottom Paint?
Interestingly, aluminum doesn’t actually require a protective coating of paint. When it comes into contact with other metals, aluminum is a good material for a boat as it is resistant against other hard surfaces, and both fresh and saltwater.
However, bottom paint is essential for preventing marine growth such as algae or barnacles, as these can affect the speed and maneuverability of the boat. As a result of this, boats require more fuel from the engine, which results in more money spent on fuel.
Do Aluminum Hulls Need To Be Painted?
Aluminum hulls don’t necessarily need to be painted, as the aluminum surface will form their own oxide as a layer of self-protection. However, to ensure the ultimate protection of the hull, it’s always worthwhile to paint an aluminum hull to protect it from marine growth.
What Kind Of Paint Do You Use On An Aluminum Boat?
The kind of paint to use on an aluminum boat depends on which part of the boat you intend to paint. For the parts of the boat that are mostly exposed to air and not water, paints that are combined with primer work brilliantly.
For the bottom of an aluminum boat, you’ll need to use an antifouling paint, as this will help to prevent barnacles and algae from adhering to the surface. This is because of the biocides that are released in the paint, which work to repel such marine growth.
How Often Does A Boat Need Bottom Paint?
On average, a boat will need bottom paint to be reapplied once a year. This is generally enough time for the layer of antifouling paint to be rendered ineffective. However, if you regularly remove your boat from the water after every use, then the bottom paint can stay on for around two years.
On the other hand, if you leave your boat in the water for extended periods, the paint will need to be reapplied every year during its annual check.
How Long Can You Leave A Boat In The Water Without Bottom Paint?
Boats can typically last up to 3 or 4 days in the water without bottom paint before it starts to develop any kind of marine growth. Algae, barnacles, weeds, or slim will start to adhere to the surface after the boat has been left stagnant in the water without movements after this time.