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How to eliminate boat odors

The causes of the pong, and how you can get rid of them

Smells are small amounts of the parent material “gassing” and sensed by “dendrites” inside our nose. So if a material does not gas (such as steel) it has no smell.
Environmental factors such as temperature and humidity affect the gassing process.
To eliminate a smell we have to remove the source and dilute the remaining concentration with more air.


Airflow is a must in removing stale smells, so open the hatches, install fans, and put up a wind-scoop.
The most common boat odours come from:
• Dirty bilges
• Holding tanks and head systems
• Bacteria and mould growing inside the boat
• Gassing from leaked petroleum products on a hot engine
• Fish residue

Dirty bilges

Bilges eventually collect everything lost, dripped, spilled, or regurgitated on the boat. Because there is no airflow, a slow release of the “smell” will waft from the bilge.
The simple trick is to fill the bilge with hot, fresh, soapy water. Use plenty of detergent, and let the mix sit for a while before clearing the bilges.

Be sure to remove all materials stored in the bilge that can hold smell (cardboard, paper, and cloth).


Head odours

The odour may be resident in the toilet, the hoses, in the holding tank, or spills left over from past clogs.

The first step in eliminating the smell is a simple acid flush. Use a mixture of Muriatic acid and fresh water. A mild solution of one litre of acid mixed into a 20 litre bucket of water and slowly pumped through the head hoses will dissolve the thick residue inside.

Follow the mixing instructions on the bottle and leave the mix sit inside the hoses overnight. Remember to pump a little acid then change the outlet valve configuration pumping again to work the flushing acid into every hose, and finally into the holding tank.


Hose smell

To check if a hose is “odour impregnated” wrap a rag soaked in hot water around the hose at its lowest point. After the rags cool give them the sniff test. If the unpleasant odour has transferred to the rag it’s time to change the hoses.

Be sure to check the toilet outlet hose, the vent and the holding tank outlet hose.
Hint - Flushing with fresh water (and occasionally with acid) can make head hoses last nearly forever. A less aggressive method is to flush a litre of vinegar down the head every month. Let the vinegar sit in the lines, breaking up deposits.


Head intake hose

The intake hose of any salt water system is prone to a build up of micro-organisms that give off a distinct “rotten” odour when the head is flushed. Over time this organism can infect the complete head system.

To kill the micro-organisms pull off the intake hose at the hull and suck up a bleach/fresh water mix (10:1). Continue to pump till the bleach mix has completely filled the inlet hose and the smell of bleach is present in the toilette.

Once the bleach is inside the inlet hose let it sit for a few hours before pumping out.
Vent hose

The vent from the holding tank can be a steady source of odours through the cabin. In severe cases carbon filters can be added to the head vent hose to catch the odour before it reaches deck. On larger vessels the vent can be led overhead to the radar arch, or up a mizzen mast.
It’s possible for the head odour to end up back in the boat due to pressure differences between the deck and cabin. One solution is to hook a small fan to the vent hose that keeps a slight negative pressure in the tank.


Sink and gray water smells

Gray water has a distinct stale grease smell. The source may be the gray water tank, the shower sump or often the sink trap.


Gray water

Gray water tanks need complete cleaning every few years because oil and grease washed from the body can combine with soap to form a thick gooey substance coating the bottom of the tank. This slime is organic and will eventually begin to rot, giving off a repulsive odour.
Scooping the slim from the bottom of the tank is one easy solution. Alternatively, the evacuation pump can be left on while a powerful hose breaks up the slime allowing it to be sucked out while in motion.


Sink traps

Sink traps hold heavy grease, hair, and other contaminants. The typically recommended method of cleaning the trap is to take it apart and clean the elbows individually.
Another solution is to pour hot water down the drain then use a plunger to break up the held material.



Mould not only makes a boat smell stale, it can cause respiratory problems, headaches and even long-term illness.

Protect yourself by wearing a respirator and long gloves during the de-moulding process.
Use a mixture of vinegar with a cap full of bleach in a bucket of water. Wipe all exposed surfaces and let the mixture dry. Remember, bleach does not kill till it dries, so wipe the bleach on and leave it alone.

Pull all sheets, towels and anything else that can be washed from the boat. Run it through the laundry adding a small amount of bleach and hang in the sun to dry.
Impregnated mould

Removing mould that has gotten into the wood or the interior can be a challenge. A pan filled with a strong bleach solution and left open in the cabin with all the hatches closed can help as a shock treatment to the living mould.


Ozone generators

Put the ozone generator inside the cabin, close the hatches and let it run.
It’s best to leave the boat unattended during an ozone generation cycle as ozone is not good to breath. If the ozone is noticeable as a smell the concentration is too high to be safe. Leave the area till the treatment is complete.

Let the boat air for a day or so before re-occupying. Repeated ozone treatments are often needed.


Chain locker

Water dripping from the anchor chain contains bottom muck, and small amounts of micro organisms that will begin to decay once inside the boat.

To remove the smell use a deck wash down hose to clean the chain as it comes aboard. Next, separate the chain locker from the main bilge to contain the messy water where it can be easily pumped overboard.

To clean dirty chain lay out it out on the dock, scrub out the interior of the chain locker and wipe it down with a mild bleach solution. Let the bleach completely dry before replacing the clean chain.


Engine odours

Many odours come from petroleum products that have spilled or leaked onto the engine, “gassing” once the engine has reached operating temperature.

The easy way to deal with these is to clean the engine completely. Locate any new leaks and fix them.

Be sure to use an electric engine room blower whenever the engine is running and continue to check for new engine leaks.


Fishy smells

Fish begin decaying moments after dying, and also contain a high percentage of oil that helps the odour to impregnate into any substance it touches.

Start with a good cleaning of the affected area with a detergent and bleach mixture. Let the area soak, and then rinse. The detergent lifts the fish oils, and the bleach kills the bacteria.

After the area has dried sprinkle baking soda and moisten with a fine spray of water. Leave to soak for at least 15 minutes, followed by a good scrub of the baking soda. Leave to soak again, then rinse.




   © Team Yachtwork 2007