Please ensure your boat is in less than 2 knots of tide or current for your appointment time and date. Low tide is best if you are not berthed in a marina with lock gates.

Frequently Asked Questions

Here are the answers to some of the questions we are often asked about concerning hull cleaning and scrubbing using a KeelCrab underwater drone.

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Question Answer
Where should my boat be? On a finger berth in a marina is ideal. It's even better if the marina is locked or gated so that there is no tide or current to deal with. Hammerhead pontoons are OK, but you will be asked to turn your boat around half-way through the scrub.
Are you cheaper than a lift out or using diver(s)? Nearly always, yes. Some divers may clean hulls unofficially as part of their hobby, but when working professionally they need to dive in twos for safety reasons, so costs go up. Lift outs involve much more plant and equipment as well as people, so tend to be significantly more expensive.
What sort of drone do you use? We use a drone that was developed under the EU Horizon 2020 programme called a KeelCrab.
Is the drone going to remove the antifouling that is currently on my boat? No - the brushes that we use are ANCCP certified and do not remove antifouling paints that are well applied and properly bonded to the hull. They only remove vegetation and algae build-up. You can read more about the brushes on this dedicated page.
What sort of boat can you scrub? Modern sailing yachts with smooth hulls and bulb keels will benefit most. If you have many ridges (e.g. a clinker built hull or pronounced keel bands), or a hull with a long keel then although the drone will remove some of the build-up, you probably won't be happy with the results so we recommend that you don't book with us.
Do I have to be there when my boat is cleaned? Yes, we need you to be there in case of any questions or problems (such as electricity supply).
Do you need electricity? Yes, the pontoon must have a RCD protected 240V AC supply using the standard boating leisure plug found on most pontoons, or a standard UK 3 pin plug, or a European 2 pin plug.
Is it safe to use 240V AC in the water? No, so instead the drone uses a low voltage power which it derives from the tether cable. This goes back to a box on the pontoon, where the 240V AC power is supplied.
Do I have to operate the drone myself? No - we will steer the drone and operate it for you.
Do I need a fresh water supply? Ideally yes, as it is good for us to rinse off the drone once it comes out, but if this isn't available, don't worry as we can rinse it off later.
How long does it take? This depends on the size and hull configuration of your boat. The bigger the boat and the more complex the shape, the longer it will take. We offer appointments in varying lengths of times aimed at different boat sizes. We clean at a top speed of 2m squared per minute.
How much fouling can you remove? About 90% will normally come off, but this varies depending on how badly fouled your boat, strength of any tides and the length of your appointment (the longer your booking, the more we can remove). Regular scrubbing produces the best results and actually prolongs the life and effectiveness of most antifouling paints.
How stiff are the brushes? We offer three different brush types, soft, medium  and hard stiffness. We will recommend the correct brush for you based on the amount of growth on your hull (which is normally medium stiff).
What certification are the brushes? The brushes are ANCCP certified.
What are the brushes made of? Nylon or stainless steel wire. Please see this page.
How deep can you go? We can only go to a maximum depth of 10m.
Can you inspect hulls? There is an IP68 rated High Definition camera with powerful LED lights that allows us to see the bottom of the boat very well. The lights and the camera are focused on a point about 30cm away from the front of the drone, so long range vision is generally poor. The visibility is determined by the state of the water, so we see better in clearer waters and murky waters are very difficult to see far in. If you need to inspect a hull for any specific purpose, then you are probably best to use some other method, but if you want to see the bottom of your boat whilst cleaning is going on, then this is going to be perfectly adequate. (Please see the next question for more details).
Can I have a video of the bottom of my boat? Yes. Connect your phone or tablet to our WiFi network and download an app called WiFi View. You will then be able to view the same images as the operator and record video or take pictures as you please. When connected to the video WiFi hot spot please note that your phone will not have internet connectivity. We do not offer training or support on the use of the WiFi View application.
Will the brushes remove barnacles? No. Using brushes that remove barnacles could damage the antifouling or hull itself.
Can you get into really tight spaces? No - the drone is 42.5cm wide and long. On most boats we can clean approximately 90% of the boat beneath the waterline, but this does vary from boat to boat based on the design.
Can you clean a keel/rudder? In theory, yes. However, the practicalities of doing so vary tremendously from boat to boat. Some keel/rudder configurations lend themselves to easy cleaning (such as those which have a gentle fairing in joint to the hull), whilst other configurations (such as those with a 90 degree angle to the hull) are much more difficult. Tidal conditions also impact the ability of the drone. Check with your drone operator on the day. 
Can you clean a propeller? No
Can you go around underwater obstacles such as impellers? Yes, mostly as the drone is steerable. However, there is a trailing cable that the drone is tethered to that can catch on protrusions. Therefore, we recommend that you always put in place an impeller (speed log) blanking plug and consider other delicate areas as required.
Can you work in strong tides and currents? No, only up to a maximum of 2 knots of flow. Stronger current than this makes directional operation of the drone difficult.
Can you work in strong winds? Generally up to about a F5 or 6 we can continue working, however if the boat is moving substantially on its mooring and causing jerking motions then this can dislodge the drone from the hull. In sheltered locations we might be OK even up to a F7 or above whilst it is safe to work on the pontoon. The use of snubbers (mooring compensators) can help reduce snatching and jerking to a point. On small boats with lifting keels having people walking about on the boat and causing it to rock violently from side to side can also cause problems.
Can you work in very murky and low visibility water? Yes, but we can't see where we have been if it is really bad visibility which means that we will probably miss small patches. Generally we can see enough though.
Can you clean bow thrusters? We can only clean up to and around the bow thruster, not in the tube or thruster itself.
My boat is very heavily fouled. Should I use your service? No - a lift-out would be a better solution for you.
Are you insured?

Yes, Knowledge Tek Ltd is underwritten by Royal & SunAlliance Insurance Plc. Our limits are:

  • Employers liability - £10,000,000
  • Public liability - £5,000,000
  • Professional indemnity - £5,000,000
I've got a race coming up - will this be useful? Yes. Alex Thompson at Hugo Boss racing is an example of one person who benefits from hull cleaning with KeelCrab. (note: although not through our service)
My boat is in saltwater/freshwater, can it be cleaned? Yes, we can operate in both freshwater and seawater.
Does my antifouling paint need to comply with any regulations? Yes. Most antifouling paints will already comply with EU regulation 528/2012 BPR concerning biocide regulation, but if yours does not, then you should not book a scrub with us.
Please note that during the Brexit transition period your health and safety responsibilities have not changed.
Coronavirus / Covid 19 / Social Distancing is a concern to me. What H&S policy do you have? Please see this page for a specific update on Coronavirus.


And here are some of the answers to questions about our website.

I only want part of my boat cleaning. What should I define as the length? The minimum we charge is for 6m/1hr waterline length, so please select this product. (small boat option)
Why do you have different boat cleaning products? We book different lengths of time for different boat lengths, to give us enough time to clean your boat. Smaller boats take less time, so have a proportionally smaller appointment slot.
My boat is located in an area where I cannot see you operate. Will you come to me and clean my boat? This depends on your location. Please contact us by email at and we can try to work out a suitable arrangement. You will be asked to pay for travel costs in some circumstances, depending on your location.
Do you clean commercial boats as well as leisure craft? Yes, as long as the boat is suitable and not too big.
Can you clean tanks / swimming pools? Yes, depending on what they are holding and other requirements such as access to an electricity supply. Please contact us at and outline your requirements.