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A steel houseboat hull: when is an ultrasonic survey due?
Short answer
There is generally no fixed date for a private houseboat,
but an older steel hull should come out regularly and have its plate thickness measured by
ultrasound.
Before buying, before new cover and whenever anodes or paint look wrong, it is due.
Steel houseboats on the Thames, on the canals or in Dutch and Belgian harbours often stay on the same mooring for years without ever coming out. While the coating holds, steel lasts a very long time. The trouble is that nobody sees what happens below the waterline. Rust creeps on under blisters in the paint, stray current from shore power or neighbouring boats eats the sacrificial anodes and then the hull, and inside the boat the bilge rusts under ballast and floors. A thin hull is often only noticed when it gives way in one spot.
For a private houseboat there is generally no statutory interval. Surveyors and underwriters still want to know what state an older steel hull is in, and that is shown by a survey with ultrasonic thickness readings at many points: the waterline, the chines, the bottom plates and around the skin fittings. The usual triggers are buying a used houseboat, changing insurer, anodes that disappear unusually fast, blistering paint or rust streaks. Many owners also bring the boat out at regular intervals to clean and recoat it, and a diver can check anodes and coating in between.
So set the date yourself before a leak sets it for you. Ask for the survey to list the measured plate thicknesses with their locations, not just an overall verdict, so next time you can see how fast the hull is losing steel. Look at the shore power installation: an isolation transformer or a galvanic isolator helps against stray current. And keep the invoices for anodes, coatings and surveys. After water comes in, an owner who can show the hull was looked after is in a far better position when the question is whether corrosion or an accident caused the leak.
Worth remembering
Paint
blisters, rust streaks and fast wearing anodes show there is a problem
Plate thickness
only an ultrasonic survey shows how much steel is left
Have the hull measured before a leak answers the question for you.
Questions
What owners ask us about this
How often should a steel hull be surveyed?
For a private houseboat there is generally no fixed interval. A survey makes sense before buying, before new cover and when anodes wear unusually fast or the paint blisters. Older hulls should come out at regular intervals.
What does the surveyor check on a steel hull?
Plate thickness by ultrasound at many points, the coating, welds, anodes and skin fittings, and the bilge from the inside. Ask for the readings with their locations.
Why does shore power affect hull corrosion?
Stray current can flow through the earth of the shore supply and attack first the anodes and then the hull. An isolation transformer or a galvanic isolator in the supply reduces that risk.
Related
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