Thru-hull Fitting Emergencies
Stay Afloat After Thru-hull Failures and Reduce Their Occurrence
Oct 12, 2006
Most boats have at least a few thru-hull fittings. As the name implies, thru-hull fittings are penetrations going through the hull of your boat. They serve many purposes. Thru-hull fittings can provide water for your live bait well, raw water for engine cooling, drainage for the galley sink, or allow a bilge pump to discharge. Many of these fittings are installed below the waterline.
What does a thru-hull fittings look like?
Thru-hull fittings have an external flange that rests against the outside of the hull and use a gasket to help prevent leaking. The fitting has a threaded cylindrical body that goes through the hull, and an internal flanged nut that tightens the fitting to the hull. The interior end of a thru-hull fitting can have a shut-off valve or have a barbed end that accepts a hose held onto it by clamps.
Suggestions for thru-hull fitting maintenance
- Install thru-hull fittings made of corrosion resistant material like brass or nylon. Ensure its construction material is compatible with the hull material.
- Use a quality marine sealant during installation
- Replace existing hose clamps with new corrosion resistant clamps annually. Use two clamps at a time on the thru-hull fitting.
- Inspect thru-hull fittings every few months. Many are hard to see and are not maintained. Exercise attached valves to ensure they are not stuck open.
- It is a good idea to close the valves on thru-hull fittings while a boat is stored for long periods. Don't close valves on above board cockpit drains during storage.
Emergency Actions
Having a valve on the interior of a thru-hull fitting can be very useful in the event of a hose failure. As you can imagine, the failure of a thru-hull fitting installed below the waterline is a true emergency. An amazing amount of water can flow through a small hole down in the water a couple of feet.
Carry tapered wooden plugs sized for the thru-hull fittings used on your boat and put together a simple damage control kit. Some manufacturers even build thru-hulls with external caps that can plug the opening during an emergency. Review the article on Vessel Damage Control for more hints on how to prepare for potential emergencies.
