How to clean a boat hull

As a boat owner, you’ll be aware that there are several cleaning and maintenance protocols to adhere to in order to maintain a boat’s performance and value, one of which is cleaning the hull.

If you are new to boating, you may feel a little overwhelmed when trying to keep up with all the terminology and contemplating how you will clean the part of your boat that sits in the water. Or, if you’re an experienced boater, you’ll likely be in agreement that boat hull cleaning is a crucial element of any boat cleaning and maintenance routine.

Like it or not, your boat’s bottom should get cleaned – at least occasionally.

We asked Richard Snowball, Marina Manager at Val Wyatt, the best way to clean a boat hull and how often should it be done?  Here’s a round-up of what we discovered.

First, let’s be clear on definitions, as many boating newcomers get confused about which part of the boat constitutes the hull.

What is the hull of a boat?

The hull of a boat is from the bottom of the keel (the flat blade sticking down into the water from the boat’s bottom) up to the rubbing band, the profile strip that protrudes slightly to protect the boat’s hull when berthing.

What are the topsides?

The topsides refer to the parts of the boat between the waterline and the gunwale or deck level.

What is the superstructure?

The superstructure consists of the boat’s parts that project above her main deck, from the rope fender and above.

Top tip: If you are new to boating, definitions can be confusing, so if you are getting your boat hull cleaned by a professional, check to see if they are cleaning the topsides (waterline to gunwale) or below the waterline to keel, which is normally antifouled. It might also be worth reading our beginner’s guide to boating terminology blog.

Why do boat hulls need cleaning?

A crucial aspect of being a boat owner is keeping your boat in good condition.

Hull cleaning below the waterline prevents its corrosion and the excessive growth of algae and other marine life, which causes waterline staining. The more dirt and growth you have on a boat’s bottom, the more drag there is when it travels through water.

What is the best way to clean the hull of a boat?

There are different cleaning methods according to the type of water the boat is in, and many cleaning products and implements are available. Cleaning will also depend on the material the boat is made from. People will want to know, ‘how do you clean a fibreglass boat hull?’ or ‘how do you clean a wooden boat hull?’ for example.

For this Q & A, we focus on fibreglass boats on inland waterways in freshwater, but we’ll also touch on a few aspects of cleaning both sea-faring and wooden boats.

The most prominent challenge for cleaning the hulls of fibreglass boats that live on the UK’s freshwater inland waterways is that of limescale, which sticks to the boat’s hull just from the action of it going through the water. There’s also a boat’s vulnerability to aquatic life growth. This build-up of plants, algae, micro-organisms and small marine creatures on submerged surfaces is called biofouling or fouling.

To the untrained eye, this can look like green or brown slime. A newcomer to boating may not know boat terminology, so they may simply ask, “How do you clean the brown off the bottom of a boat?”

So, let’s get to the crux of cleaning your boat’s hull. Firstly, it is always best to have your boat lifted out of the water for the most effective cleaning.  The best steps to clean the hull are as follows:

1. Lift the boat out of the water.
2. Jet wash off the antifoul or brown slime under the waterline.
3. Use a biodegradable limescale remover* to remove limescale from the topsides.
4. This will remove the chalky white marks, so the boat looks better.
5. The UV will fade the hull so the next step is to use a polishing machine to compound it (a bit like T-cutting a car) to bring back the shine.
6. Add a UV resistance wax.

*Note that limescale remover is acidic. Ideally, cleaning should occur over a filterbund (a receptacle that collects the cleaning fluid and water). This will ensure the water run-off can be filtered and contaminated waste doesn’t go into the river.

It’s also worth noting that soft antifoul paint is more likely to come off during the cleaning process and has chemicals in it that shouldn’t go back into the river. The hard antifouls, however, are much more resilient to cleaning.

What do you need to clean a boat hull?

If the boat is lifted from the water, the essential equipment to clean a boat hull properly includes a heavy-duty jet washer and a polishing machine. Val Wyatt uses only high-quality equipment to ensure the best cleaning.

There are many hull cleaning products, including detergents, limescale removers and polishes. At Val Wyatt, we are conscious of the environment and will always choose environmentally friendly brands.

For polishing, Autoglym car polish works equally well on the hull of a boat – we’ve tried and tested many options and have found this to be the best wax polish – after the hull has been compounded.

The compound used depends on how badly the hull has faded. A six month old boat, for example, will only require a mild abrasive whereas a boat that is ten years old and hasn’t been cleaned for five years will need a harsher abrasive at first, then work down to a finer compound before putting the wax on top. The marine surface finishing brand we use at Val Wyatt is Farécla. Again, we’ve tested quite a few, and this one comes out on top.

You will also need microporous cloths to finish off.

How do you clean your boat’s hull if it is still in the water?

It’s impossible to thoroughly clean the boat’s hull while it is still afloat, but it’s still possible to start on other parts. Thick limescale and algae will be at their worst near the waterline because this area gets light and air.

The waterline area of the hull can be reached and cleaned using a long handled brush from the deck or, better still, by launching a dinghy and working around the boat. The bravest boat owners may choose to don their swimwear and clean their vessels from in the water. Whichever method, make sure the brush you use is soft enough that it does not scratch the hull.

Some people use a hosepipe to spray it down and use Bio-Cal shower cleaner, but there is then the issue of cleaning products entering the water.

How long does it take to get a boat’s hull professionally cleaned?

Professional hull cleaning takes around four hours for a 20 – 25 ft boat. This involves a jet wash, compound and polish, plus time to lift the boat out of the water and relaunch it after cleaning.

When is a good time to clean a boat’s hull?

There’s no ideal time to clean a boat’s hull other than when most convenient. Most people, particularly those who have their boats lifted out of the water over the winter will want their boats looking tip-top in time for spring. Taking this into consideration February / March is a popular time.

Pre-spring is a great time to get everything cleaned, from the antifoul to the canopies and the teaks to ensure that your boat looks brand new when it goes back into the water. Boats moored at floating marinas and not lifted out of the water might be cleaned a little later – however, much will depend on the weather and how warm the Spring is.

In addition, some boat owners like to get an extra clean in during the mid-summer months without the compound polish to prevent limescale and algae from building up.

We offer a full complement of competitively priced standard and specialist boat maintenance and cleaning services, including:

• Compound polishing
• Antifouling
• Pressure washing
• Lift and relaunch
• Teak cleaning
• Full valet

At Val Wyatt, in most cases, boats are lifted out of the water for the winter between October and November when they are jet-washed and cleaned, with polishing taking place in February and March before they go back into the water.

Cleaning the hull of sea-faring boats

Sea-faring boats or those in saltwater will have to contend with salt and mineral deposits, plus any algae, scum, water lines or oxidation marring the hull. Saltwater leaves salt stains on the hull and boat surfaces that can be hard to remove if not taken care of promptly. Read more about how to remove salt deposits from your boat here.

A crucial tip for cleaning the hull of wooden boats

Wooden boats are a whole different ballgame. To clean the underside of a wooden boat, use a soft brush and NOT a jet washer because jet-washing can damage the caulking and wood.

Val Wyatt

We are an established, independent marina located on the River Thames in Wargrave. We are passionate about helping our customers to find their perfect boat and have the best possible experience once they take to the water. We offer a wide range of services, including a brokerage for new and used boats, storage, and a full suite of professional cleaning, maintenance, and repair services.

Call our friendly team now to find out more about our services.