Hints and Tips



Exhaust Muffler Waterlock Issues

Guide to possible solutions


For a period in the late 1990’s and into the 2000’s several Jeanneau sailboat models including the 42DS, 43DS, 44i, 45DS, 49DS and Jeanneau 53 had their engine exhaust muffler water-locks installed as unit within the engine bearers. Many of these installations have required repair or replacement.

Layout in SO42DS


Early muffler designs were typically fabricated from stainless steel, which unfortunately could subsequently corrode and result with water leaks and potential exhaust gases leaking into the engine compartment.


Stainless steel systems need to be carefully built with the correct material and welds if not the exhaust gasses will interact, for example with any nickel in the welds and eventually fail. 

If rebuilding then low carbon AISI 316L must be used and welding should be done in an inert argon atmosphere. All welds then need to be acid cleaned and correctly passivated to ensure they will last.


Later models were often plastic roto-moulded units. Both types suffer from being quite awkward to inspect and access. These plastic roto-moulded types were used into the late 2000’s in designs including the SO42DS.


Whilst original parts might be available from Jeanneau France for some models, several owners have decided to replace with a Vetus plastic option, which are now commonly fitted as OEM by many yacht builders, including Jeanneau.


This is often considerably lower cost option and avoids the risk that the replacement part, if stainless steel would also have a short lifespan. They are also much easier to inspect.


When planning a Vetus option it is important to calculate the water-lock volume and also install the new exhaust run at the correct height, to ensure there is no risk of the new exhaust system filling with water and back flowing into the engine. There are a wide variety of Vetus Waterlocks types available and professional guidance is recommended before finalising a choice.


Typical factory installation of a Vetus waterlock in a SO35 Model


Specific Issues

There are a number of different threads on these issues on the forum and FaceBook group, so to provide an overview I have summarised key points below along with photos of specific model installations with links to the original forum discussion.


Sun Odyssey 37

Whilst this did not have the muffler integrated in the engine bearer, the original in-line stainless and rubber muffler can be prone to rusting, so should be checked if it has not already been replaced.

Consult this thread for more information SO37 Muffler thread


Sun Odyssey 42DS

Some models were fitted with plastic roto-moulded units within engine bearer. These can suffer leak at the joints that can be hard to make gas and watertight.


42DS muffler within engine bearer


Consult this thread for more information SO42DS Muffler thread


Sun Odyssey 43DS

Many 43DS models have suffered corrosion and leaks from the original stainless mufflers.


Additionally these units are very hard to remove, even the fuel tank probably has to be removed. Any sign of corrosion of the muffler at the visible forward end should be taken as a warning that the unit is reaching the end of its service life.


Some 43DS owners, rather than remove the old muffler, have bypassed it entirely with a new Vetus unit installed in parallel. The old muffler can be slid forward enough to allow a 90 bend to be installed to allow connection to the new system water-lock which can be installed next to the P bracket.


An alternative below shows where a 43DS has very tightly installed a Vetus unit within a modified battery compartment


Consult this thread for more information SO43DS Muffler thread


Sun Odyssey 45DS (and probably similar on SO44i and SO45)

It appears that both stainless and plastic roto-moulded units were fitted at different production times.

The stainless version shown above can be very difficult to remove as the flange can corrode and may need to be cut off in situ to remove.


45ds with and without brass threaded insert


The roto-moulded type were later modified with a brass screw insert as shown above. The spigot does not come as part of the kit so must be ordered separately and maybe about 15mm longer.


The woodwork surrounding the companionway will have to be removed which can be awkward due to the engine insulation material.


One alternative option is to fit a replacement at the front of the engine and duct the exhaust through the engine bearer as shown below:

Consult this thread for more information SO45DS Muffler thread


Sun Odyssey 49DS

Karl Kirkman reported on the Jeanneau Owners Facebook Group his experience and solution on his SO49DS which I have summarised:


Our initial plan was to replace the existing leaking stainless with something like a Vetus. But due to the layout, there was no way this could be done without making major modifications. The exhaust hose runs just under the floor and is level almost all the way aft. If we tried to place a muffler under the beds, between the fuel and water tanks, we would have induced an 8-inch (20cm) rise in the hose. This would have trapped water between the engine and the muffler.


The closest we could come to installing a Vetus without causing this rise would have been around the steering quadrant, which my mechanic strongly advised not to do, as it was too far from the engine to effectively trap exhaust water. Both the mechanic and I came to the same conclusion. The best location for the muffler was right where Jeanneau designed it to be, in the stringer under the engine.


To extract the old muffler I had to pull up the floor just aft of the engine as the hose clamps for the back fitting were unreachable, then to get the muffler out of the stringer, we also had to pull the floor immediately forward of the companionway stairs up because of the length of the muffler. It took three weeks to make a new muffler made out of G10 fiberglass as each piece had to be epoxied in, one at a time and then allowed to cure before the next piece was fitted.


The installation took two days as the top fitting had to be epoxied in place after the muffler was installed. To be on the safe side, we let the resin cure overnight.


Finally as a note of caution, engines of course always require seawater for cooling, but additionally with the plastic water-locks there is a risk that they can melt if the engine is run without the seacock on… This happened to this unit on a SO 44i.


Above article is based on original posts from the Jeanneau Owners Forum and Facebook Group

Thanks to the contributing owners for the photographs and knowledge,