Skip to main content

The charity making life better by water

Hull maintenance

Regular hull maintenance is essential for keeping your boat afloat. Licence support advisor Debbi Figueiredo explains more about what you need to do and what to look out for.

A boat in dry dock at Tooley’s Boatyard

Whether your boat is made out of steel, wood or plastic there will be times when it will need to come out of the water for essential maintenance. Steel boats are usually removed from the water for 'blacking' every two to three years. As the owner of an older narrowboat, the regular chore of hull blacking is always combined with a slight anxiety about the condition of the hull. This is fuelled by most marine insurance companies' paranoia of sinkings, which leads to their demands for a hull condition survey when a boat reaches milestone birthdays.

Time for a survey

This year was a milestone birthday for our girl and there was no escaping a hull condition survey to keep our boat properly and comprehensively insured. For our own peace of mind too we wanted an ultrasound check to ensure that whatever electrical problems had plagued the hull in her very early life had not returned.

For those of you who don't know, steel-hulled boats can turn into a fizzing electrical battery which corrodes the steel if there are stray electrical currents around. And one thing you don't want your boat to be is a colander! This is why boats have anodes fitted, as these fizz away instead of the hull's steel.


We booked a week in dry dock at our local boatyard last year along with a surveyor. You often have to book a long time in advance, especially if you want a summer month or you moor in an area with a lot of boats.

Into the dock we went on a Saturday morning in February and our surveyor arrived just as the water receded from the dock. Much to our relief the first sight of the hull below the waterline in four and half years was very good, despite having delayed blacking to coincide with the 30-year survey. Even as the last of the water was pumped from the dock, pressure washing and the hull survey commenced. It's amazing how much water weed and wildlife, like mussels, you find stuck to the hull and it takes some effort to get it off.

Pressure washing a narrowboat

Good preparation is the key

After pressure washing, any loose paint and stubborn bits of marine growth need to be removed with a wire brush, either manually or with mechanical help. Finally, any areas of rust need treatment with a rust converter/anti-corrosion protection product before painting can begin.

Much to our relief the ultrasound results of our hull survey were very good indeed and no new pitting was discovered. However, next time we dock, we're going to have to scrape the bottom, paint it and fit extra anodes to the base plate, in order to guarantee that it outlives our lives on the boat. There's definitely two schools of thought regarding the painting of base plates, with those for and those against. It's a horrible job, often working in a very confined space.

Removing loose paint from the hull with an angle grinder

Protecting the hull

The final stage of docking is the painting of the hull. In the distant past tar was used to paint boat hulls. More recently bitumen-based paints or Two Pack Epoxy Paint systems are used for steel hulls. GRP or plastic boats use hull treatments that prevent osmosis.

On this occasion we used a new bitumen water-based paint instead of a traditional bitumen paint. We always try and get at least five coats on below the waterline and at least two above the water line. The new paint allowed us to do eight coats below the water line and four above over the course of four days, before we had to stop painting and allow drying time. It will be interesting to see how it has lasted the next time our boat is out of the water.

Letting the water back into a dry dock

Floating the boat

Late on our final night at the yard it was time to flood the dock again so as to be ready to leave the following morning. It's a relief when the hard work is over, but you do still worry whether the paint is sufficiently dry and whether or not you are going to scrape it off again once you leave the safety of the dock. As the water rises the boat's running gear slowly disappears from view and she seems to come alive again on contact with the water.

Last Edited: 27 July 2023

photo of a location on the canals
newsletter logo

Stay connected

Sign up to our monthly newsletter and be the first to hear about campaigns, upcoming events and fundraising inspiration