If your narrowboat's baseplate or hull sides are pitting and your surveyor has mentioned overplating, the first question is usually how much it will set you back. This guide breaks down what affects the price, what is genuinely worth doing, and how to avoid paying for steel you do not need.
Overplating means welding new steel plate over an existing hull section that has thinned through corrosion. It is most common on the baseplate and the waterline band, where pitting tends to be worst on older boats. The new plate is fitted over the original steel rather than replacing it, which keeps the job manageable while restoring structural thickness.
It is a structural repair, not cosmetic. A good job is fully seam welded and the cavity between old and new steel is treated or sealed so you are not trapping water and starting fresh corrosion underneath.
As a rough guide, full baseplate overplating on a 50 to 60 foot narrowboat often falls somewhere between £4,000 and £9,000, with most jobs landing in the middle of that band. Smaller patch repairs or a single waterline band can be considerably less, sometimes from a few hundred pounds upwards. These are realistic ranges, not quotes, because every hull is different.
The biggest cost drivers are the area to be plated, the steel thickness used (typically 6mm or 8mm), access, and how much grinding, cleaning and preparation the old hull needs first. A boat that needs the baseplate, both sides and the swims will naturally cost more than one needing a single band.
Not every pitted hull needs overplating. A hull survey with ultrasonic thickness readings tells you the real picture. If your baseplate started at 10mm and is reading 7mm fairly evenly, you may have years left and overplating would be premature spending.
Overplating becomes sensible when readings drop towards 4mm or below, when pitting is deep and localised, or when a surveyor flags it for insurance or a sale. Get the readings before committing, and be wary of anyone recommending a full plate without them.
Most overplating happens with the boat out of the water, so you will usually need a yard with a slipway or hardstanding along the Medway, the Thames or the Kent coast. Some jobs can be done afloat for the upper hull, but baseplate work needs the boat lifted.
When you ask MMA Welding for a price, we would rather see thickness readings or come and look than guess over the phone. Honest measurement up front saves you paying for steel the hull does not need, and it means the quote you get reflects the actual job.
A full baseplate job usually takes one to two weeks of working time, plus drying and blacking. Smaller patch or band repairs can often be completed in a few days.
Yes, adding 6mm or 8mm steel over a large area adds noticeable weight, which can slightly lower the boat in the water. A good welder will factor this in and advise where plating is genuinely needed rather than blanket plating everything.
Properly done and documented overplating generally satisfies insurers and surveyors, and can make a boat insurable again. Keep the welding records and a follow up survey, as insurers may ask to see them.
Tell Michael about your job. Drop a quick message with what needs welding, where it is and a photo if you have one. He will come back the same day.