Connecting equipment to an existing thru-hull or installing a new one can make anyone nervous. After all, an analysis of  BoatUS Marine Insurance files shows that about 20 percent of boats sinking at the dock are caused by thru-hull issues. But with some common sense and the right materials, you can rest well knowing your boat is secure.

First, keep in mind that any hole below the waterline has the potential to quickly sink a boat. In our BoatUS study, leaking thru-hulls, included stuffing boxes, baitwell discharges, washdown fittings, transducer plugs, bow thruster hoses, broken scuppers, and failed head discharges were all examples of leaking thru-hulls that sank boats. Your thru-hulls should all have operable seacocks that can turn off the flow of water with a 90-degree turn of the handle.

Clamps (all stainless steel) on hoses should be snug and free of rust. Two clamps are better than one if they can fit over the spud. Hoses at thru-hulls should be the reinforced type, which is usually a heavy black hose. Lighter, unreinforced PVC hoses can (and do) rupture and crack.

Check the entire length of the hose, as excessive heat from the engine or chemicals (bilge cleaners, battery acid, spilled fuel, and so on) can cause isolated failures. Replace hoses that are suspect — mushy, hard, and/or cracked. And should all else fail, it’s important to tie on a soft wood plug at every thru-hull in case of emergency.

Prevention Any “opening” in the hull, whether it’s protected by a seacock or stuffing box, needs to be inspected periodically. The same is true for openings that are slightly above the waterline. Seacocks should be operable. Any that are “frozen” open or shut should be taken apart and lubricated.

— Charles Fort FOR BOATUS