That is the stark warning from boatyard experts who have just had to replace a bow thruster tube that leaked - and replace hundreds of pounds worth of fittings.
Many modern boats are built with bow thrusters - a circular steel tube crossing the bow of the boat below the waterline with a central propeller that pushes water out on one side or the other.
The problem, according to Simon Jenkins, boss of Norbury Wharf on the Shropshire Union Canal is that the tubes are vulnerable to corrosion and difficult to maintain.
“They are often just a piece of 6mm steel tube and it can be difficult to paint them from the inside, as you would the rest of the hull as you can’t easily access the centre of the tube where the propeller sits.
“Some of them have a mini weed hatch above the propeller for clearing weed but whole sections of the tube are essentially out of reach.”
The problem showed up at Norbury when manager David Ray noticed one of the boats on a mooring was sitting low in the water. Closer investigation showed about six inches of water inside the boat all along its length. It took some time to discover where it was getting in and staff had to remove woodwork and hack away spray foam around the bow to get to the bow thruster tube.
“When we cleared the spray foam we found the leak,” said Simon, “it seems that pitting developed in the steel tube around the propeller and at the end the spray foam must have been the only thing keeping the water out of the boat.”
He says every boat owner with a bow thruster should inspect them carefully every time the boat is out of the water and attempt to ensure the tube is treated with the appropriate paint to prevent corrosion.
“It won’t be easy,” he said, “as most of these bow thrusters are very difficult to access but it has to be done because they have introduced a potential weak point to the boat’s structure.”
Is there a solution? Simon is not optimistic: “The problem is in the build stage. It may be that builders need to think about heavier steel or even stainless steel for these tubes. They are probably subject to wear because the propeller mechanism throws the grit and other solids in canal water onto the sides of the tube with some
force and this may be the reason for pitting the steel which allows rust to get in and rot the tube.
“We can only suggest everyone keeps a close eye on them and treats them at every opportunity.”