Home . Articles . How-to . Boat Doctor . What’s with the sour smell on my boat?

What’s with the sour smell on my boat?

2023 March 1

Dear Boat Doctor,

I keep my boat on a mooring, so it’s usually closed up, and it doesn’t really have any ventilation.  I notice a sour sort of smell whenever I get on board.  It’s not horrible, but I’d like to eliminate it if possible.  I’m pretty sure it comes from the bilge. Any suggestions?

Jon Bawabe

via email

Dear Jon,

The source of the smell is likely to be the bilge, which tends to be dirty, wet and poorly ventilated, all of which is a recipe for odors.

A dry bilge is a happy bilge, so you want to do your best to keep the bilge dry. I know this is nearly impossible, but search out any leaks and fix them.

If you can’t keep your bilge dry, at least keep it clean. Be especially careful with any wastewater that flows in the bilge: ice box drains, shower or sink drains, and any leaks from the head should be avoided at all costs. None of these should ever be allowed to enter the bilge. Sink drains should flow directly overboard, and icebox and shower drains may need to be drained into a sump and pumped overboard.

Speaking of the head, if the smell is like sewage or sulfur, your head hoses may be “leaking.” I don’t mean leaking liquid, rather hoses that have become permeable over time and will release smell. A good way to test this is to wipe down the hoses with a wet rag. If the rag becomes smelly, you likely need new hoses.

Start with a thorough bilge cleaning. Some people will tell you to pour some bilge cleaner in the bilge and go sailing to let it slosh around, but it only works in a bilge that’s already clean. I recommend you access the bilge as much as possible, scrub it, and hose out the residue.

Next you should address the lack of ventilation. A flow of fresh air down below and a way to exhaust stale, damp air will certainly help. There are a variety of solutions to allow air in and out. A classic solution is a vent in your companionway boards with a grate, downward angle saw cuts or another solution. Many people ventilate a deck hatch. Lewmar makes a small vent that matches well and isn’t leak-prone. Marinco offers several solar-powered vents that can be mounted in a hatch or, with a lot more work, directly in the deck.

If you find the source of the stink and get some air moving down below, your boat will be sweet smelling in no time.