How to Clean a Boat Hull: Best Methods

Updated January 5, 2022
Man using pressure washer to clean boat hull

It can be hard to keep your boat perfectly maintained and pristine. Learning how to clean a boat hull will help you preserve the value of your vessel and enhance its performance.

Learning How to Clean a Boat Hull

If you can't afford to hire a pro to clean your boat hull, you can do it yourself by following these simple steps. But first, you need to grab a few supplies.

Man cleaning and painting a boat’s hull
  • Heavy-duty boat hull cleaner
  • Dri-diver
  • Bucket or hose
  • Large sponge or rag
  • Muriatic acid
  • Soft bristle brush
  • White vinegar
  • Baking soda
  • Dawn dish soap
  • Spray bottle
  • Star Brite instant hull cleaner

Basic Cleaning

When it comes to basic cleaning, you just need to follow these steps.

  1. Use a low-power hose or bucket of fresh water to rinse the hull as thoroughly as possible. You want to get rid of the salt build-up and loosen any algae or mold that may be attached to your boat hull.
  2. Choose a cleaner specialized for the use of boat hulls and mix it with water as directed on the product's label.
  3. Either rig up a dinghy alongside your boat or use a dock-based product such as Dri-Diver to scrub every section of your hull down to the waterline.
  4. Use a large, soft sponge and dip it into the cleaning solution. Wring out the sponge slightly, then wash each section of the boat hull from the dinghy. Take care not to damage the hull's paint job. Use gentle strokes in a circular pattern. You can also employ a bow-to-stern motion if you are using a heavy-duty cleaner.
  5. Once you have finished scrubbing the hull, rinse it with fresh water.
  6. The final step requires a second sponge soaked with clean water. Use this sponge to wipe off any residual cleaning solution and watermarks.

Extensive Cleaning

For really tough jobs, it's best to use muriatic acid (or another acid-based cleaner) and a strong hose to clean your boat hull.

Man washing boat hull with long handle brush
  1. Use the hose to thoroughly rinse your boat hull, making sure to remove any barnacles, weeds, or other slime.
  2. Combine the muriatic acid and water.
  3. Spray the muriatic acid mixture directly onto the boat hull and let it sit for about two minutes. If you still see dirt, grime, or moss growth at the end of two minutes, allow the product to sit longer, but not more than 10-15 minutes.
  4. Use a soft bristle brush to remove excess cleaner and grime.
  5. Repeat the cleaning process on the opposite side of your boat.
  6. Rinse the entire hull thoroughly, making sure to eliminate all residual acid from the hull and trailer as it can sometimes cause rust spots and corrode.

Natural Method for Cleaning Boat Hull

When you are looking for a more natural method for cleaning your mildly dirty boat hull, grab the baking soda and white vinegar.

White vinegar and baking soda with scrub sponge and white towel
  1. Mix 2 cups of water, half a cup of baking soda, half a cup of white vinegar, and a few drops of Dawn.
  2. Mix the ingredients together well and allow them to settle.
  3. Pour it in a spray bottle.
  4. Spray down the hull.
  5. Allow it to sit for a few minutes.
  6. Use the soft bristle brush to scrub away all the scum.
  7. Rinse the area well with a hose or a bucket.

How to Spot Clean a Boat Hull

When it comes to spot cleaning stains on the hull of your fiberglass boat, you want to reach for the instant Star Bright cleaner.

  1. Get your boat dry and out of the water, if possible.
  2. Add a bit of the Star Bright hull cleaner to a rag or sponge.
  3. Wipe the cleaner over the spot.
  4. Allow it to sit for the recommended time.
  5. Rinse the area well with a hose.

Boat Hull Cleaning Products

There are a variety of boat hull cleaning products available on the market. Some of the most popular include:

  • Muriatic acid--This product is recommended for use on boat hulls that are extremely algae-covered or have extensive moss and barnacle growth associated with long-term water moorage. It is available at major discounts stores such as Walmart and pool supply shops and home improvement stores, such as Home Depot and Lowe's.
  • Star Bright buffered acid--This product is recommended for mildly dirty boat hulls.
  • Zing hull cleaner--This specialized hull cleaner must be mixed with water as directed on the product's label and can be used for basic cleaning jobs.
  • On/Off by Maritime Products Company--Use this product if you are cleaning along the waterline and portions of the boat bottom that are not painted. On/Off is powerful, so it's best to use gloves when using it. If the product comes in contact with skin, it will burn. Likewise, if it comes in contact with paint, it will cause streaks. The product is corrosive but will not harm the gel coat, and it neutralizes with water.

About Cleaning a Boat Hull

Boat hulls are constantly exposed to the elements. Consequently, they sustain heavy abuse. This is especially true if you travel in polluted water, though regular trips in salt or freshwater can also lead to hull corrosion and barnacle growth. By maintaining a clean boat hull, you will help preserve the integrity of your entire vessel. In addition, keeping your hull shiny and smooth will help you move through water at a faster rate.

Experts recommend cleaning your hull several times a year, depending on how often you use your boat. One option is to hire a professional boat hull cleaner. Pros use special scuba gear to dive under the water and thoroughly clean parts of the hull that are difficult to reach. Professional hull cleaners can get your boat looking shipshape again, but they don't come cheap.

Other Cleaning Options

Learning how to clean a boat hull by hand takes patience and practice. If you don't desire to rig a dingy to your boat to scrub the hull, consider using an automatic boat wash system. These systems consist of a hull-leaning machine equipped with two brushes that rotate horizontally along the hull, and another two brushes, which rotate vertically at the heel. The automated system does not use toxic chemicals and is similar to an automatic car wash; only it washes boats as they sit in the water.

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How to Clean a Boat Hull: Best Methods