How to Clean A Boat Hull

How To Clean A Boat Hull | Fiberglass Or Aluminum

It is the hull of your boat which takes the brunt of the punishment during use. Knowing how to clean a boat hull can be quite helpful and can save your money as well. The hull is exposed to both salt and fresh water, the elements, and the abrasive chemicals present in water pollution, all of which can damage your hull over time.

Therefore, correct and timely hull maintenance is essential in protecting your investment. If the hull is properly maintained, your entire boat remains seaworthy. However, corrosion, filth, and barnacle growth can not only damage your hull, but cause greater resistance, end up slowing you down, and if you own a motorboat, this results in increased fuel costs.

How to Clean A Boat Hull
How to Clean A Boat Hull

Cleaning your own hull is not as hard as it sounds, and if done on a regular basis, it will be quite simple. Remember, the best way to keep your hull in excellent condition is to do regular maintenance.

If you let a few cleanings slide, it will be harder to clean due to barnacle growth, thick layers of algae, and grime. The following is a basic guide on cleaning a boat hull yourself and covers cleaning both in and out of the water, procedure, and supplies needed.

Types Of Boat Hulls

The more you know about your boat’s hull, the better off you will be when it comes to proper hull maintenance. If you are new to the world of boating, we encourage you to become familiar with the type of hull you have, as well as the material it’s made from. There are two different types of boat hulls: Displacement and planing

Displacement Hull

The displacement hull is what you see when you observe sailboats. This hull is designed to assist the boat in cutting through the water, or ‘displace’ the water quickly, with as little resistance as possible.

Boats with this type of hull are slower than those with planing hulls but will give a smoother ride. Keeping your displacement hull clean and waxed equals a 12 percent increase in efficiency according to the International Maritime Association.

Displacement Hull Shapes

  • Round Bottom

This is the most commonly seen displacement hull shape. This gives you a nice, smooth ride, but can roll and become unsteady at times.

  • Multi-Hull

This displacement hull gives an extremely stable and smooth ride but does not take corners well.

Planing Hull

If you’ve ever seen powerboats race, you know how they seem to skip over the surface. These boats have what is called, a planing hull. These hulls are specifically designed to rise up and skim the surface of the water as the boat picks up speed as their motor propels them forward.

So, where the displacement hull moves water aside, the planing hull rises above the water. When cleaning different types of planing hull, don’t forget to give it a good waxing, as many boaters feel this helps the boat move through the water more quickly, and less resistance means less wear and tear on your motor.

Planing Hull Shapes

  • Flat Bottom

If you plan on boating in shallow, calm waters, then the flat bottom planing hull is what you’ll want. It does not do well in rough waters, however.

  • Deep ‘V’ Hull

A planing hull designed to give you easy, and smooth handling at high speeds and in choppy water.

The Negative Impacts On Your Boat Hull

Impact Of Water On The Boat Hull
Impact Of Water On The Boat Hull

Out of sight, out of mind. Nice saying, but not so nice when it applies to your boat’s hull. What you don’t see happening to your hull while in the water, can cause you great expense and damage to your vessel over time. In just a very short time, a wild and uncontrolled growth of algae and barnacles can accumulate on your hull, negatively affecting your fuel efficiency, hull integrity, and overall engine performance.

In a very short space of time, ‘bio-slime’ will begin to form on your hull. Bio-slime is a slippery layer formed by bacteria and other microorganisms, which then become host to weeds, algae, and finally barnacle growth.

The more growth on your hull, the less efficient your boat becomes due to an increase in friction between the growths and surrounding water. All of this will cost you much over time if not tackled immediately, followed by a proper, monthly maintenance program for your hull. Knowing how to clean a boat hull yourself can save you both time and money.

Cleaning A Boat Hull In Or Out Of The Water?

You may either choose to wash the hull of your boat with the boat in the water or out of the water. Only boat owners who are certified scuba divers should consider washing their hull while the boat is in the water, as you will need to wear scuba gear in order to clean below the boat’s waterline or those comfortable free diving.

If you are not scuba certified, or comfortable free diving, please hire a professional hull cleaner to properly clean your hull while the boat is in the water. Each method will require a different procedure as well as different supplies. In this guide, we’ll go over the basics of how to clean your boat hull underwater, as well as out of the water.

How To Clean And Wax Your Hull When Out Of The Water

1. Gather Your Supplies

Make certain that you’ve taken the time to create a detailed list of all the items you’ll need to clean your hull ahead of time. You don’t want to arrive at your boat, ready for a day’s work, only to realize you forgot an important item. So, create a list and proceed to gather everything on that list in one place, ready to take to your boat.

Maintaining the integrity of your boat hull cannot be understated. In other words, when considering soaps and detergents, please use ‘marine grade’ boat hull cleaners, buffers and waxes only, as they are formulated to be gentle to your hulls surface finish.

Also, for best results, purchase only brushes, microfiber towels, sponges, and cleaning mitts specifically designed for boating. To help get you started, we’ve included a list of supplies you’ll most likely need:

  • Buckets
  • Hose
  • Access to Fresh Water
  • Hull cleaning soap and wax
  • Several sponges or quality microfiber towels
  • Heavy duty gloves

2. Washing The Hull

Once your boat is out of the water, you can begin to clean your hull. Before you get started, make certain that you’ve covered the interior of your boat if you do not wish it to get wet. The first item on the list is to hose any loose grit, grime, algae, sea salts or filth from your boat. If you do not have access to a freshwater hose, you can consider using a bucket filled with fresh water. Only use fresh water on your hull, as salt water may cause your hull to yellow.

Once the hull is good and soaked, inspect it for any slime or grime. Take one of your sponges, or a high-quality microfiber cloth, and gently remove any filth. ‘Gently’ is the operative word here, as you want to avoid scraping or scratching your boat hull. This is where the question of power washers often come up. While some boat owners may use a power washer, we recommend that you stick with your hose and sponge not to risk damaging your hulls protective finish as much as possible.

3. Remove Old Wax

Next, you’ll want to remove any old wax from the hull’s surface. Take some microfiber towels and use your favorite boat wax removal solvent. Let the solvent do the work for you so you don’t have to scrub hard. Please only use products specifically designed for removing wax from boat hulls. If unsure, check the label, it will state if it is for ‘marine’ use.

4. Soaping Up The Hull

We’re at the point now, where we are ready to apply our soap. Proceed to mix your chosen soap as per directions. A good quality boat hull cleaner will be able to remove scum, scale, any light oxidation, algae, yellowing or chalking, and be an environmentally friendly, biodegradable product. Follow the directions of your particular hull cleaner to the letter. Using a proper boat cover you can partially reduce the damage to the boat by the weather.

Some hull cleaners may use a boat body brush, others only sponges. Please remember to wear heavy-duty work gloves when cleaning your hull. Apply the soap with a clean sponge or microfiber towel. Let the soap do the work for you, letting it sit on the surface, softening up the grime, slime, and filth, for about 10 to 15 minutes. Rinse with clean, fresh water. Repeat the process if necessary.

5. Time To Apply The Buffing Compound

Take your chosen buffing product in hand, as it’s time to get to work buffing your boat hull. Always keep in mind that you want to avoid scratching the protective finish on your boat hull, at all costs.

That being said, polishing and buffing products are generally abrasive in nature, designed to refresh your hull, making it shine like new before wax is applied, so don’t use too much pressure.

Following the directions on your chosen product begin to buff in short sections at a time, only. Depending on your personal preference, you may buff by hand or use a specially designed buffing tool. Try to keep your hand pad or the buffing tool flat and equally distributed.

6. Apply The Hull Polish

Once your hull is buffed to your satisfaction, you may now proceed to apply the polish. Application of the hull polish is similar to that of the buffing compound.

As always, for best results, please follow the instructions for your particular product. Once finished, give your boat a final hosing with fresh water, to remove any loose dust or dirt. This is an important step before you begin to apply the wax.

7. Waxing Your Hull

Make certain that you only use an appropriate boat wax which is made for your type of boat. Waxing functions to further protect the surface of your hull from the water and the harmful chemical pollutants often present which can damage your hulls surface.

How you apply the wax is a personal preference, as you may apply it with a power buffer or by hand, moving in tight, controlled circular movements. If your brand of wax states to allow it to dry, then let it sit for about 5 minutes or so. Once you notice it becomes dry and cloudy, it’s time to buff that area with a quality microfiber towel, to a lovely, bright, reflective shine.

You can also choose to paint your boat. Knowing how to paint a boat, it will be more appropriate to paint it in many cases.

How To Clean A Boat Hull In The Water

1. Preparing To Clean Your Hull Underwater

Cleaning Boat Hull Underwater
Cleaning Boat Hull Underwater

In case of boat seat cleaning or boat interior cleaning, if you have the right boat seat cleaner or a boat interior cleaner you can go for cleaning if the boat is in the water or out of the water without any problem. Now, in case of a boat hull, it is different.

While many boat owners perform maintenance when the boat is out of the water, there are those who are able to wash their hull while it is in the water, using scuba gear to work on the hull beneath the waterline.

Other boat owners choose to free dive, using a mask, fins, and snorkel, which is much more time consuming and tiring as well. If free diving, you may choose to use some dive weights to help steady yourself while working.

If you are new to boating, learning how to clean a boat hull underwater is not as hard as it sounds.

However, as previously stated, do not choose the scuba method unless you are properly scuba certified before proceeding, if not we strongly recommend you hire a professional hull cleaner who is certified.

2. Gather Your Supplies

  • 6-inch putty knife
  • 1-inch putty knife
  • Small wire brush for propeller and rudder only
  • Carpet scraps or microfiber towels if hulls have ablative paint

3. Dress Properly

Make certain that as much of your skin is covered as possible, to lessen the risk of being cut by sharp barnacles. Light, long sleeve shirts and loose-fitting pants should do fine.

Remember to wear gloves to protect your hands as well. Also, only clean your hull underwater when the current is calm. Never start a cleaning process if the waters are rough and choppy. If the waters become rough during the cleaning process, leave the water immediately.

4. Begin The Cleaning

Start by using a soft cloth or sponge to gently remove any algae, slime or filth. Once you have finished, it’s time to concentrate on the barnacle growth.

We cannot stress enough, the importance of removing the barnacles without scarring, scratching, or scraping the surface of the hull. Take your putty knife and delicately pry away any barnacle growth, taking great care to not mar the surface of the hull.

There are some boat owners who believe that metal scrapers remove too much of your hull’s paint, so use only plastic.

When you clean, start from the top of the waterline, and work down from there. This prevents you from being scraped by barnacles when you surface.

If you purchase a hull cleaning kit that has stainless steel pads and brushes, use them on unpainted areas only. Under no circumstances are you to scrub or scrap hulls with ablative paint, only use soft sponges, or carpet scraps. If you see a cloud of paint rising, stop cleaning immediately.

5. Propeller, Rudder, And Thru-hulls Cleaning

For these jobs, it’s best to use your 1-inch putty knife to prevent damaging these areas. For the thru-hull, a flat head screwdriver should work just fine.

Make certain any small openings are also free from slime, grim and growth using very small wire brushes. When these areas are free from debris and growth, your engine will run more efficiently and be less stressed, which also improves your fuel economy costs.

Fiberglass Boat Hull Cleaning

The steps to clean a boat hull will remain unchanged in case of fiberglass boat hull cleaning. Let’s go through the steps again:

  1. Wash the fiberglass hull and remove the dirt from the surface
  2. Clean the harder stains
  3. Buff and polish
  4. Wax the hull to shine

But we should take some extra care when working with fiberglass. The fiberglass dust is bad for health as it can produce irritation in our skin, eyes and respiratory system. We should protect ourselves using musk, goggles, and long clothes to cover our skin. Hand gloves are essential too.

Don’t use hard brushes or steel wool to clean fiberglass. Use microfiber towels or, nylon brush applying with circular movements. A soft sponge can be used for more difficult stains.

The soap or cleaner should not contain bleach as bleach can damage the fiberglass surface. A paint remover will help to remove the boat bottom paint and the top side paint. You can try marine grade cleaners with phosphoric acid to remove the rust or hard stains produced by the water.

Try to wash your boat after every outing with soap and fresh water to maintain the fiberglass perfectly for a long time. Taking care of your fiberglass boat it will shine around fifteen years without any problem.

Aluminum Boat Hull Cleaning

For cleaning an aluminum boat hull the method and the steps will be the same as described above for a boat hull. So, wash, clean, polish and wax the aluminum hull maintaining the sequence.

  1. For washing freshwater hose and hot water will do better. It will remove the external grit, grime, algae, sea salt, and dirt. You can use microfiber towels or soft sponges to remove the external elements.
  2. Now when selecting the cleaning product we must take an appropriate cleaner which is specially made for cleaning the aluminum boat. Use the soft nylon brush and microfiber clothes or soft sponge with the circular motion to apply and scrub the boat hull. Don’t use hard brushes but repeat the process if necessary one or two times more.
  3. Polish and wax the boat with proper polish and wax made for aluminum boat and must be marine grade. Many people like to use just a marine grade aluminum boat paint.

Aluminum always reacts with the weather and produce oxidation. So, if you don’t go for winter fishing on your boat, cover the boat with a good boat cover to protect the boat as much as you can.


As you can see, learning how to clean a boat hull yourself is not that hard. Properly maintaining your boat hull every month will not only keep the integrity of your boat intact, but will also increase its lifespan, and be cost-effective in the long run.

If your hull is coated with slime, grime, growth, and barnacles, you’ll lose valuable fuel efficiency, and even risk your motor overheating and burning out sooner, due to the increased work needed to propel it through the water.

While you can hire professional boat hull cleaners, you can also choose to perform this task yourself, either above water or underwater. Both methods have different procedures and supplies, so it’s a good idea to be familiar with each method. If you love to do small boat jobs of your own, how to mount a trolling motor can be interesting for you.

Leave a Comment