A Pro’s Troubleshooting Guide to Boat Odors

Interior odors are one of the most common complaints people have about their boats. Mold and mildew are probably the most common sources of interior odor but often are joined by blackwater or greywater in producing an interior space that’s unpleasant to spend long periods of time in.

First and foremost, keeping the boat clean is half the battle of keeping it smelling clean. However, many people find this easier said than done. Compared to a house, cleaning aboard boats is complicated by the marine environment, the additional systems that are also more tightly packed, and less frequent use of practically everything. It’s important to routinely check and clean bilges, AC condensate drains, icemaker niches, water heaters (replace your anodes!) and any other areas where a leak or condensation could cause moisture buildup. It’s also a good idea every so often to check on the freshwater connections around the boat – particularly if someone has worked on them recently. We’ve seen instances on superyachts where a tiny leak at one of the hundred or so freshwater supply connections led to significant interior damage after going unnoticed for years. Bilges and equipment where seawater stagnates can generate the foulest odors on the boat. Heads that are plumbed with seawater rather than freshwater are a common culprit and are always recommended against.

One issue we often encounter and frustrates some owners and crew is freshwater odors. Typically first presenting at one or two of the heads, it can spread across the rest of the freshwater system if left unchecked. Essentially this is the buildup of bacteria in the freshwater plumbing. Sometimes the entire freshwater system will smell bad. This is often caused by filling the water tanks through a carbon filter, which removes the chlorine that is intended to prevent bacterial growth. It’s possible to treat bacterial buildup by dosing chlorine dioxide into the freshwater system and running water through all the faucets and heads, but it may require multiple treatments over a long period of time. Another chemical option is dosing household bleach (sodium hypochlorite) either at the freshwater lines producing the odor, or into the freshwater tank at about 50-100 ppm. Be extremely careful when calculating and measuring bleach doses as excessive doses present a health hazard. Best practice is to also replace the sections of tubing or supply hose that run to offending heads or faucets, since bacteria can be harbored in places somewhat protected from bactericidal agents. As with everything else the sooner this issue is addressed the easier it is to resolve. Usually by the time it’s identified it has not spread very far beyond the supply connection to the toilet itself, and it virtually never happens on boats with chlorine or silver ion dosing systems. Predictably, UV sterilizers are ineffective at mitigating this issue, since it is spreading back from the ends of the system rather than from the storage tank. If your boat does not have a silver ion sterilizer, the best way to avoid bacterial buildup in your freshwater system is simply to run water through faucets and flush toilets regularly.

Now to blackwater and greywater odors. These come broadly in two varieties – continuous or intermittent. Oftentimes continuous odors need time to build in stagnant air before becoming noticeable and can be mitigated just by establishing some airflow. But this doesn’t mean the underlying cause should be ignored. If an interior space goes unused for a while the odor may begin clinging to surfaces and will present much more of a nuisance. A common cause of continuous odor is hose permeation – something that can happen over a few months in many types of hose not designed to prevent it. It can be difficult to tell if a hose is permeated. Often any low spots that sewage sits in between flushes will be discolored a little and may be sticky. The best method we have found is to take a dry paper towel and wipe the outside of the hose – if the paper towel has the telltale odor afterward, the hose is permeated and should be replaced. Note that not all of the hose will become permeated at the same rate. Sections with low spots where greywater/blackwater stagnates will permeate in a much shorter time than the rest. For this reason, it is not always necessary to replace all the old hose on the boat, but we recommend getting as much out of the way as practical. It’s also good to do it proactively, if you know the boat was built with odor-permeable hose. Both types of sanitation hose sold by Environmental Marine — Odor-Safe and Yachtflex — are designed to be impermeable to odors for several years; typically, a dozen or more.

Intermittent blackwater and greywater odors can have a wider variety of causes. Commonly, the issue is a design flaw with the vessel that allows fumes exhausted out of holding tank vents in the hull sides to be reintroduced to the boat. Luckily, there’s a straightforward fix. Activated charcoal vent filters can virtually eliminate this type of odor. They have drawbacks – vent filters need to be changed regularly. At minimum once per year, and more with heavy use. If they are not changed out, and the vent filter clogs, it can cause system-wide issues. But if they make the boat more enjoyable to use, vent filters are well worth the maintenance.

Another common cause are small leaks in holding tanks that allow air within the tank to escape, causing the tank to vent into the boat’s interior. This can either be the primary issue or a symptom of another issue like a vent restriction that forces displaced air through the path of least resistance. These can be hard to track down even by marine sanitation professionals. Typically pinpointing the source requires a smoke machine and a few helpers around the boat to watch for smoke as the problem is reproduced. It’s also necessary to ascertain why the tank began venting into the boat in the first place before declaring the problem fixed. For example, fuel vent fittings have flame arrestor screens, and some boat builders use the same vent fittings for holding tanks. The flame arrestor gets clogged, and the air forces a way out of the tank. Even when the cause seems obvious (corroded tank fitting, poorly installed hose, etc.) there may still be a vent restriction, and sealing the tank will lead to greater pressure buildup in the tank and the possibility of something failing spectacularly. Make sure the vent line is clear.

We hope this helps you in eliminating odors aboard your boat. If you have any questions, or an odor problem you’d like assistance in addressing, give us a call. We can offer answers immediately or refer you to industry service experts who help people with these same issues every day.

At Environmental Marine, we’re always happy to help — so feel free to call us at 1-800-522-2656 between 8 a.m. — 5 p.m. Monday through Friday with questions. Often, we can offer an immediate answer.