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Drilling holes in the superstructure, what are the requirements?

I want to fit some navigation lights to my narrowboat. This requires me to drill some holes in the steel superstructure, both for wiring and for screws to attach the lights. Are there any special precautions I should take to avoid these holes becoming rust points, and are there any other areas I need to bear in mind?

Asked by: Rod Nelson  | 1.21pm, Monday 9 October

WW says:

The only holes needed in the side of a narrowboat for navigation lights are for the fixings and a larger one for the electrical connection cable.
To stop rust developing around these holes, the light needs to be sealed against the panel. Assuming they are to be fitted onto an already painted boat, silicone or a similar flexible sealant should be applied around the edge of the light base before the final fixing. Self-tapping screws are the easiest fixing to use but it is important to get the correct size pilot hole; too small and it is impossible to screw it into the metal, too large and the thread will not bite.
An often overlooked point is cable protection from damage against the steel edges. Rounding the edges with a file will help as will a spot of paint which will also prevent rust. A grommet is the best solution if you can find one of the correct size, alternatively a small piece of plastic pipe fitted over the cable will provide extra protection. It is also important to make sure that the earth connection is insulated and does not make contact with the steelwork, as this will lead to galvanic corrosion.

Rupert Smedley  | 3.45PM, Monday 9 October

Readers say:

when you drill the holes put a magnet near the tip of the drill bit to help catch the steel scarf generated, also use the magnet to clear any filings that fall onto paintwork , if left they will form rust spots in the paintwork.

John McDonald  | 11.35AM, Monday 27 November

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