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
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
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
Be sure to remove all materials stored in the bilge that can hold smell
(cardboard, paper, and cloth).
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.
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
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
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.
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 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 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
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.
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.
Put the ozone generator inside the cabin, close the hatches and let
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.
Water dripping from the anchor chain contains bottom muck, and small
amounts of micro organisms that will begin to decay once inside the
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.
Many odours come from petroleum products that have spilled or leaked
onto the engine, “gassing” once the engine has reached operating
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.
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.