cleaning the bottom of a boat

Cleaning the Bottom of a Boat – A Practical Guide

We usually spend a significant amount of time and money cleaning the bottom of a boat while she is resting in the yard. We then gain a false feeling about how solid everything is below the waterline.

There is only water down there, what could possibly go wrong?

You would be very surprised at what can go wrong if the preventive measures are neglected!

Let’s have a look at what is actually happening below the waterline.

What Is Fouling Of The Boat Hull?

It is a slowly growing (literally) problem; marine life loves to settle on your hull. Once you start skipping the cleaning a bottom of a boat from time to time, the problem shall come.

Barnacles, mussels, marine worms grow quickly.

One day you’ll suddenly discover a whole “coral reef” on the sacrificial anodes and on the echo-sounder sensors; and the tiny speed-log prop will start sending random data or no data at all.

This is what we call fouling, this is why anti-fouling coating of the bottom is necessary.

Fouling Of The Boat Hull
Barnacles on the bottom of a ship in drydock.

The anti-fouling coating, despite the “anti” in its name, does not stop life spreading but it only makes the marine creatures struggle harder.

Your boat shall slide smoother and run faster if you clean the bottom regularly. Otherwise the sea monsters’ colony invades the territory of your boat bottom, blocking or damaging your underwater instruments, seals, maybe a shaft and a propeller too,unintentionally of course.

Marine scientists find about 4000 species that can start life as fouling on your hull.

Why To Clean a Boat Hull?


  • Perform cleaning the bottom of the boat regularly.
  • It is not safe and is expensive to carry a marine zoo with you.
  • Choose an anti-fouling brand thoughtfully.
  • Fouling increases the fuel consumption.
  • Fouling may cause overheating of the engine, consequently damaging it.
  • Fouling decreases the cruising speed dramatically.
  • Fouling also affects the maneuverability!
  • Fouling may block seacocks and instrument sensors.
  • Fouling (when at the disaster stage) can affect tilting a boat, or slow down maneuvers, even making some of them nearly impossible.
  • Do not underestimate cleaning the bottom of your boat.

When It’s Time To Clean The Hull Of A Boat

First – use your eyes.

Second – as soon as you feel the max cruising speed and/or acceleration decreasing or fuel consumption rising, clean the hull. Either or both of these may indicate that a beautiful colony of mussels are traveling along with you.

They mate, die, reproduce their charming mollusk-cubs, right on your hull, and incorporate their hard as a stone exo-skeletons into your anti-fouling coating – which is nearly a disaster stage.

Aye-aye, captain, you will never get the smooth surface back again until your next dry-docking, once you neglect the preventive cleaning with a C-pole. Don’t let it go that far.

However, once it has happened, you need to get things back on track. This article is about how to minimize the “sponsorship” you’re providing to the barnacles and the underwater worms. Those eat your budget by fuel consumption growth, also increasing the amount of time and money at the next dry-dock.

Preventive Cleaning Is The King

For preventive cleaning the C-pole is a beautiful solution as a tool. It is trouble-free, there is no diving needed and there is no possible damage for the coating. Use it regularly, and you can ignore the rest of this article.

in-water hull cleaning tool C-POLE

How To Clean The Bottom Of A Boat In Water

For cleaning the bottom of a boat there is no need to pull her into the yard every time. It is very expensive, and time consuming (and weird).

There are other ways to clean the bottom of the hull, including:

  • Hire a diver.
  • Be a diver.
  • Use the tide.

Diving Recommendations To Clean The Bottom Of A Boat In Water

Disclaimer This is boat care advice, not diving advice.

Diving is a serious enterprise. Using a professional diver is the safest trouble-free option, but if one is feeling romantic one may try and succeed.

Cheaper fuel consumption, higher speed and better maneuverability are the immediate fruits you shall gain. However, doing it on your own, don’t aim to clean it totally, but only adding a comfort to your cruising adventures.

I repeat, never expect the absolutely clean bottom, when doing it in water. But if you want it professionally clean – hire a pro.

Set of Tools You’ll Need

A scrubber. A “marine scrubber” is best due to its quasi sickle-shape for sake of a better reach. Its special design is just more convenient.

Use it carefully, applying no damage to the coating. In general, avoid “scrubbing” until necessary as a rule of a thumb, but feel totally free when cutting the upper layers of the unwanted weeds and barnacles, carefully and slowly.

A brush, as a softer alternative for a marine scrubber. Better have both onboard just in case, but a timely use of a brush or a C-pole or a combination of two will cancel the scrubber. Leave the latter for an emergency.

marine scrubber brush boat bottom cleaning
Marine scrubber and soft brush are best for cleaning the boat.

Other Recommendations

  • Cleaning the bottom of the boat is rarely very urgent.
  • Choose the best weather: comfortably warm water, sunny, calm sea, no waves, no wind, no movement of the boat otherwise it may hit you severely, etc.
  • Consider anchoring where the water is cleaner, rather than in the marina. Having a dinghy may be convenient for the purpose.
  • Turn off all electricity, switch off everything, cut the main switch, disconnect the shore power if any.
  • Cut off the engine. At minimum, be totally sure your girlfriend or a drunk buddy onboard will not fall accidentally upon the start button, when you are in water next to the propeller.
  • Do not expect to clean your hull back to “factory condition”. Better you aim to “cut the lawn”, “remove the jungle” or “make a photo of your braveness” for Instagram.
  • Clean carefully, and do not damage the underwater coating, which is more important than all other issues. Those marine barnacles can sit really tight. The anti-fouling coating is tough too, per se, but just behave reasonably to avoid a negative result.

TIP As in general, love yourself before you love the boat, make it fun. Cleaning the bottom of a boat is rarely urgent.

Using The Tide For Cleaning A Boat Bottom

This is the most intriguing advice of this whole article.

You can use the tide to strip the bottom of the boat without any dockyard or diving at all. The idea is limited to the tidal schedule at first, and to the requirement of a proper sea bed as a second.

Let us state that amateur skippers in the Netherlands and UK often perform the trick.

How It Works

You anchor the boat in a place of shallow water on the high tide, and wait until the tide retreats in a way that the boat shall be grounded. As the water continues to retreat, the boat will lie on one side opening the bottom dry.

Folks promise it comes softly enough, as we talked to a few master-sailors. Yes, this is the adventurous enterprise no doubt.

low tide For Cleaning A Boat Bottom hull
Here’s how it looks in reality. More or less.

Here are more tips and things to remember then:

  • Choose a hide-out with a proper sea bed and less wind. Preferably it’ll be sand, and certainly no rocks beneath. This is the most responsible step. Experts perform this grounding upon a muddy bottom, which is relatively bold for a first timer. So the seabed is clearly sand, flat and no rocks.
  • Check the weather in advance, and it is good to be in a paranoid mode about it. Also plan what could happen for a case of unexpected wind gusts.
  • Make sure you have plenty of food and drinks with you, as you are going to be actually “marooned” for a while. There’s no guarantee you can really walk ashore from where you are, besides cleaning the hull is the primary purpose, remember?
  • If there is a dog or a cat onboard, make sure it won’t jump out and wander away. One reason is that the high tide can quickly return, the other reason is that the poor animal can die accidentally, because the naked bottom will be more of a “marsh” than a beach. Same for yourself, please stay with the boat all the time for the same reasons.
  • Make sure you’ve tied down everything, such as tools, cutlery, stuff and belongings, and especially heavy ones and breakable ones. This should be rather obvious.
  • Understand that you do not know on which side the boat is going to lie down. The experienced skippers say that you can choose the side, as the movement either controllable or predictable, by sails, wind and anchors, but surely such is not for a first timer.
  • If you have two keels the boat shall sit on them keeping her relatively vertical position. Having one keel and two rudders most possibly keep the boat standing same straight but it all depends on the actual condition under your boat.
  • The power boats might be taking the whole trick a little easier, because of a keel shape and draft.
  • Understand that when the tide arrives back again it’ll be pushing your boat towards the shore. Understand it when anchoring at the first stage of this adventure. Using a second anchor is a good idea too.
  • Indeed you do not need a totally dry sea bottom but for the first time, as always, over-care is better than under-care.

Do not underestimate the dangers of the whole operation, including and not limited to the danger to your life. You step on this path thoughtfully and we leave the decision entirely to you.

Some people perform it for the sake of a picnic and an adventure, spending a few days, also cleaning the bottom of a boat without a rush.

Cleaning The Bottom Of A Boat – Summary

That’s it for now. I believe you already know more about cleaning the bottom of your boat. As you can see, it’s not a simple thing, but it’s worth taking care of regularity here. It will save you trouble and some money too.



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igor desperatesailors

Hi, I’m Igor, Skipper of S/Y "The Hooker". A decade ago, I conquered my childhood dream: to be a sailing skipper, own a sailing yacht. Yes, it knocked dullness out of my urban life — Read more →

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