Boat Odours And Other Headaches

[Colin Swithenbank wrote this article some years ago, basing it on an article entitled Boat Odour, It's Not All In Your Head, by Peggie Hall (a consultant on head issues) for Passagemaker magazine. He has since updated it based on his extensive cruising experiences aboard his PDQ 36, Cadenza.]

Boat odours can be troublesome and difficult to identify and resolve. While the primary candidate is likely to be the head, there are also other possible odour sources.

Head Problems

1. Intake hose

Any raw intake water, fresh or salt, is certain to be loaded with micro-organisms that line the hose, eventually dying and decomposing to produce hydrogen sulphide and mercaptans to which the nose is extraordinarily sensitive. Test for the presence of these by removing the hose from the through-hull (closing the latter first) and pumping a sterilizing solution through the line. This could be white vinegar solution, Raritan’s "C.P." (a bio-enzymatic cleaner recommended by Peggie Hall), dilute bleach, oxalic acid, or cationic soap/bactericides like Fantastic. Instead of removing the intake hose at the thru-hull, you may wish to consider removing it at the head itself (keeping the open end above the waterline) and pouring your sterilizing solution through a funnel, which makes a tight connection to the hose. A 10' x 1" ID hose should only require about one and a half pints of solution. If a sink drain is close to the head inlet hose, the inlet hose can be teed into the drain close to the thru-hull. With the through-hull closed, you can then pour sterilizing solution down the sink drain, from which you can pump it through the head; for best results, do this every time the boat is closed up.

Some claim that it is sufficient to get the micro-organisms out of the bowl and hose by flushing the head with fresh water before closing the boat. This can be done either with the teed-valve solution or more simply by pumping the head dry, then dumping a jug of fresh water into the bowl and again pumping dry. White vinegar diluted 5:1 with fresh water or Raritan's "C.P." is likely to be more effective than fresh water alone.

2. Stinky Sanitation Hoses

Test for this problem by wetting three rags with hot water and wrapping them around the lowest point on each of the three sanitation hoses (head discharge hose, holding tank discharge hose, tank vent hose). Leave each rag until it cools then smell it. If it smells bad, you've found at least one source of the problem, so you're halfway to a solution.

Consider your head-pumping habits. PDQ believes that half of the stinky-hose problem is caused by people not pumping the head enough to get the contents of the bowl all the way to the holding tank. What was formerly in the bowl then sits in the hose, which is not as odour-proof as a tank. Next cruise, pump a couple more strokes after the bowl is clear to ensure the hose is also clear (but remember that this will fill your holding tank more quickly).

If the hoses still smell bad when you re-test them, replace them. Practical Sailor magazine recommends a white plastic hose from Australia called Sealand Technology Odoursafe. (Available from Genco Marine in Toronto and West Marine stores in the US as "Odorsafe". Odoursafe is flexible but very stiff – installing it in the confines of a C&C 27 may call for careful warming with a powerful hair dryer or very hot water.)

Note that in salt water, head-to-holding tank hoses become lined inside with a malodorous, highly coherent coating which can eventually block the hose. Using lots of water for each flush can minimize its formation, but this fills up the holding tank fast. Pouring two tablespoons of white vinegar into the head every couple of days and a full cupful each time you leave the boat for any length of time will prevent this precipitate and even dissolve any that is already there. It may not be a bad strategy to replace the hose periodically.

3. Holding Tanks

Properly constructed holding tanks are rarely a source of odour. Check O-rings and hose clamps for leakage (there should be an O-ring to seal the inspection port of most types of tanks, but on boats as old as C&C 27's they may be missing; hose clamps should be snug but not so tight that they distort the hose). However, odour from the vent tube with each flush can be a serious issue. Try using more of your tank treatment or switch to another brand.

Peggie Hall claims that the main source of sewage smells is anerobic bacteria. Being anerobic, these bacteria can be controlled by ensuring that the tank is well supplied with fresh air. To that end, make sure your vent fitting and hose are clear. If possible, fit a second vent on the tank.

While we agree that anaerobic bacteria are responsible for the highly odorous hydrogen sulphide and mercaptans emitted from the tank vent, supplying air in sufficient quantities is not really feasible. A much better solution is a vent-gas "scrubbing" tube (such as the Sealand vent filter from West Marine, model 447144). At nearly US$80 for a season's protection, we consider this unit very expensive and on Cadenza we originally inserted the Odorbuster (no longer available), which at US$55 worked fine. We have since constructed our own unit from 2" ID PVC pipe with end caps drilled for 3/4" through-hulls. This unit is filled with a granulated product called Ammo-Sorb, obtainable from aquarium supply stores, with a stainless steel pot scouring pad in either end to keep the granules in the tube. It is refillable and cheap (3lb bag of Ammo-Sorb: US$12) and highly effective at intercepting odours from the holding tank vent.

Other Possible Odour Sources – (Remember, it's not always the head)

1. The bilge is another source of odour from decaying micro-organisms or diesel fuel. The primary defence is to clean the bilges regularly and if possible keep them dry. Again, Raritan's "C.P." is an excellent cleaning agent for the bilge.

2. Mildew can cause odours and staining on cushions, mattresses, clothing, headliners, etc. Prevention is the best solution. Make sure that the boat is rain-proof with a good supply of fresh air in all areas. Be sure the boat’s vents are clear to draw in and expel air; consider also powered vents like the Nicro solar vent. When the boat is to be left for an extended period, open locker doors and tip cushions up so air can flow around them. A new product that looks like a super-heavy-duty version of furnace-filter material may be put under cushions to permit airflow.

If mildew does start, bleach and sunshine are the most common mildew fighters. Cationic surfactants like Fantastic are powerful bactericides and are particularly useful on hard surfaces; lemon oil will kill mildew on teak panels (and make it look new again).

On Cadenza we have put 1/8" tongue-& groove cedar in the back of one of the problem clothing cupboards with great success. Based on this we put a frame of 5/8" cedar under the mattresses which keeps any condensation off the mattress and allows air circulation for faster drying.

3. The chain locker, an enclosed area filled with damp and often muddy chain and rope, provides an excellent breeding ground for odours, which can sometimes spread through the boat. Clean out the area and let the contents dry out completely, preferably in the sun.

C&C 27-Specific Sources

Yves Chiricota had a mysterious smell in the forepeak of his Mk V. He found that water was leaking from a portlight and from the anchor well into an area under the head sole, from which it could not drain. He eliminated the problem by fixing the portlight leak and by running an overboard drain hose from the anchor well. He also carefully cut a hole in the sole and installed a 5" inspection port so that any water that reaches the undrained area could be mopped up. He cautions anyone who wishes to do the same should be careful not to cut a piece of supporting plywood below the sole.