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Running cables through the deck is often necessary, but must be done properly to avoid leaks and structural issues. Here’s what you need to know about deck glands and fittings.
The holes in this type of deck gland must be sized for the diameter of the cables running through it. Courtesy, Scanstrut, Frank Lanier
Many boat owners drill holes in the decks of their boats with too cavalier an attitude. A better approach would be doing so with the same planning and preparation as punching a hole in the roof of your house. From antennas to navigation lights, there will always be cables and wires that must be routed to a vessel’s interior. When done improperly, however, these necessary deck penetrations can lead to myriad problems including leaks and structural issues caused by deck coring deterioration and delamination due to water intrusion.
Two popular types of fittings for routing thru-deck cables are deck glands and the venerable “gooseneck” fitting. Here’s what you need to know about each.
Deck Glands
Deck glands (aka cable clams, cable seals) are fittings mounted through the deck to allow passage of one or multiple cables. While designs can vary among manufacturers, most units use a compressible gland (typically rubber) to make a waterproof seal around the cable. The hole in this gland must be specifically sized to match the diameter of the cable being installed. This is selected at time of purchase, however, many companies also include a solid plug, allowing you to drill and customize the gland to meet your specific needs. Once the cable is inserted, tightening the fitting compresses the gland, which then seals it against the cable, preventing moisture entry.
The gland itself can be either one piece or split vertically. Split glands allow you to install cable or wires without having to remove terminal ends or connectors. Simply open the gland and place it around the cable. This saves the expense of removing and replacing connectors, while avoiding poor connections as a result of removing factory-installed connections.
A quick online search reveals a number of deck gland manufacturers and options (see “Deck Gland & Gooseneck Examples” on page 88). Prices vary based on size, material (plastic or stainless steel), construction quality, and advertised watertightness, all of which should be considered when purchasing a deck gland fitting.
Gooseneck, or swan neck, fittings accept multiple wires of varying sizes.
Goosenecks
A gooseneck fitting is an inverted J-shaped tube mounted through the deck that uses its shape and gravity to prevent water from entering belowdecks. Also known as a swan neck fitting, these are often used on sailboats to transition mast wiring belowdecks.
Goosenecks are typically 1- to 2 inches in diameter and, unlike deck glands (which are sized for specific cable diameters), will accept multiple wires and cables of differing sizes. While the downward slope of the fitting entrance helps prevent water intrusion, sealing the wires once in place from outside with silicone caulk or a bit of expanding foam adds protection. If this is in an area of the deck that may become submerged due to things like boarding seas, this latter practice is particularly important.
One installation tip is to make the wires or cables longer on the entrance side, feed them into the fitting and then add the sealant. This prevents water from entering the fitting but allows you to pull out the cables (along with the foam or caulk plug) when needed.
Deck Gland/Gooseneck Examples
Installation Considerations
Regardless of the type of fitting you choose, here are a few general tips that can be applied to both deck gland and gooseneck fitting installations:
- Ensure that the cable is located and installed to prevent being used as an impromptu hand- or foothold by the crew in rough weather.
- When mounting the thru-deck fitting, be sure to seal any exposed deck coring (epoxy is typically used for sealing wood or balsa) to prevent moisture entry, and bed the fitting with a good quality marine caulk, such as BoatLIFE Life-Calk or similar.
- Install chafe protection where necessary.
- Include a “drip loop” in the cables belowdecks prior to making any connections. This allows any water that penetrates the gland or gooseneck to drip off the bottom of the loop, rather than entering the connection or terminal box, causing corrosion.
- If a wire or cable is terminated with a connector or plug, consider whether the deck gland fitting can accommodate it or if you will have to remove and replace it during installation.