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How to Clean a Boat Hull in the Water? – 2 Easy Ways

Written by J. Harvey / Fact checked by S. Numbers

how to clean a boat hull in the water

Maintenance is a large part of taking care of your boat, and it is no doubt important to clean the hull of your vessel.

However, it is not always possible to take the boat out of the river or sea for this task. You need to learn how to clean a boat hull in the water in such circumstances.

Unsure how to proceed? Keep reading to learn more.

What You’ll Need for Cleaning Boat Hull in Water

  • Hull cleaning brush
  • Underwater work gloves
  • Goggles
  • Scraper
  • Small putty knife
  • Boat hull rotary brush (alternative)
  • Snorkel
  • Wet suit

First Method: Underwater Boat Cleaning


Step 1: Preparation

There are several things you need to prepare before beginning underwater cleaning. They not only help keep the work efficient but also safe.

The first step is to get all your cleaning tools and place them somewhere accessible. It helps if you can reach them if needed even without having to get out of the water.

You also need to wear appropriate protection; this means wearing gloves, goggles, and ideally long sleeves to protect against things that may cause injury.

Scuba gear may seem like a good item to have, but it is not something you should use unless you are certified as a scuba diver. Do wear a snorkel, though.

Next, it is best to identify your exit point from the water; a ladder or swim platform on your boat is a good example. Make sure that you know how to get to it easily.

The last point of preparation is to disconnect shore power from the boat to avoid the risk of electrocution, and the best way to do this is by physically disconnecting the plug from the power source.

Step 2: Barnacle Removal

You need a scraper to remove barnacles. One advantage of doing the cleaning underwater as opposed to out of the water and on a trailer is that barnacles are less likely to dry up and become more difficult to remove.

However, scraping the boat makes it possible to damage the paint and the hull. You may use a plastic scraper to reduce the risk of scratches, but it may be more difficult to remove bigger marine organisms.

Scrape off the growth on the hull and other parts of the boat such as the rudder.

Step 3: Hull cleaning with a scrubber

Use a boat hull scrubber to brush the surface of the hull and remove the slime and biofilm on it. Use the least abrasive scrubber first to avoid damaging the surface, especially paint.

If you have antifouling on the boat, it is best to use only a soft cloth for cleaning as the abrasive material will cause the antifouling to come off.

Begin at the water line and make your way down until the entire hull has been scrubbed. You can use a putty knife for small areas such as thru-hulls.

Second Method: Washing Your Boat in the Water With a Long Hull Brush


For people who do not have the option of diving into the water for cleaning, a scraper attached to a long, usually curved pole such as the Scrubbis rotary brush is a good option.

It requires a lot of upper body strength, but the result may not be as good as taking the vessel out of the water and cleaning it with a homemade boat hull cleaner. That said, if you cannot get the boat on land, it is still better than nothing.

The advantage of this tool is its soft material that allows for the safe scraping of biofilm on the hull without the risk of damage. You also do not need as much preparation as the first method.

How to use

  • Stand on the dock and use the long pole scrub to scrape the hull surface. This cleaning tool is long enough to reach the keel in the water, even for larger vessels.
  • Start scrubbing from the water line down to the keel and scrub repeatedly while moving from one side to the other, e.g. bow to stern. Repeat the process until one side has been cleaned entirely.
  • Move to the other side and repeat the process.

Cost to Clean Boat Hull in the Water

Professional boat cleaning services costs differ based on the type of boat and its size.

On average, small boats and those with a smaller area in contact with the water are the cheapest at around $100 base price. Vessels in this price range include pontoons and speedboats, although prices can reach up to $200.

Other vessels start at higher prices. Cleaning the bottom of a sailboat may set you back $160, for instance, but prices can easily reach up to $300 or even more for larger designs such as yachts.

Some underwater cleaning service providers give prices per vessel length, such as $5/foot. Fees increase based on how much fouling there is on the hull and how sensitive the surface is to abrasion, but being a regular client could bring prices down.

In comparison, DIY underwater cleaning prices are limited to the supplies you need, and you may not even have to spend anything after the first wash. Small vessel cleaning costs start at around $40 and go up to $80 for bigger hulls.

Frequently Asked Questions


Why is it necessary to clean the hull?

Fouling on a boat hull leads to a decrease in speed and performance, which is undesirable if you’re into racing. Plus, the accumulation of marine life can cause the vessel to use more fuel, and with the prices of gas today, any money saved is appreciable.

Effects on planing boats can be even worse as fouling can even prevent a vessel from going into plane.

How often do you need to clean the boat hull?

Frequency depends on the location, with warmer waters requiring more frequent cleaning due to how much easier it is for organism growth to build up. Cleaning every 4 to 6 weeks is enough for most boaters, but you may need it as often as weekly in certain places.

Should I use anti-fouling paint?

These are useful, but they are known to contain harmful substances that can contaminate the water. It is a good idea to consider alternative products to protect the environment.

Some good alternatives include certain non-stick coatings and copper-free paints. There are newer types of antifouling that use different technologies for repelling growth on the hull, such as those using hydrogel technology.

What are the professional tools for washing your boat in the water?

One example of a professional tool is the cavitation cleaner, which uses high pressure to remove fouling. It is very quick to use, even when cleaning the bottom of a ship, and it ensures that there is no damage to the hull surface.

However, such tools are very expensive, costing thousands of dollars.


Now you know how to clean a boat hull in the water. It’s a good alternative when you are not able to retrieve or dock the vessel, and it helps to have this bit of knowledge in your bag. Just make sure to be mindful of water conditions when you do it.

Have you ever seen anyone clean the bottom of a boat in a river? Are you confident enough in your swimming and diving to try underwater cleaning? Tell us what you think in the comments section below.

Remember to boat safely.

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