Exhaust System

Exhaust systems are either “Dry” or “Wet” systems.

Dry exhausts consist of heavily lagged steel piping and silencers leading directly from the engine room to a funnel and exiting via stainless steel tailpipes high up the mast. This assembly takes some room within the saloon spaces but is maintenance free and typically lasts the life of the vessel.

Wet exhaust design constitutes an assembly of plastic waterlocks, mufflers and goosenecks connected to the exhaust turbocharger outlet, discharging at the vessel hull side or transom. Seawater is injected at or near the exhaust turbo outlet. The purpose of the seawater injection is to cool the exhaust gas and contribute to the exhaust noise suppression.

The decision to incorporate “dry” exhaust systems in all our vessel designs was adopted after lengthy technical analysis of both “dry” and “wet” type installations. Our observations of vessels that are fitted with a “wet” type are that generally the crew, despite a high temperature alarm, has a nagging anxiety about failure of the water supply. The system requires a seawater pump which, despite a rigorous maintenance program, will always fail at some point. The question becomes “what happens to the plastic components after 2-3 minutes of being subjected to 800-1000 degree Fahrenheit exhaust gases?” Also, how does one repair such a system 1000 miles from land?

Another consideration that should be taken into account is the deleterious effect on components of the engine. While the engine is running there is of course no risk of seawater entering into the engine. However the instant the engine is shut down there is a risk the residual back pressure in the system will force seawater laden vapour into the internal parts of the engine via the turbocharger; exhaust manifold, exhaust and inlet valves. This vapour when condensed is highly corrosive and may well explain the anecdotal evidence of sudden engine failure and short engine life where this system is installed.

Other doubtful aspects of such systems is that with the vessel at anchor in rough conditions “wave slop” could be forced into the hull side exhaust discharges with the potential to flood the system.

A further issue we like to see taken seriously, and which Pacific Motoryachts is passionate about is the vessels appearance. With wet exhausts, any “soot” discharge mixed with cooling water will quickly spoil the “first class” hull finish in the vicinity of the outlets.

In view of the above, Pacific Motoryachts have recognized that with the simplicity of dry type exhaust systems; vessel safety will in no way be compromised.

The construction of a traditional funnel casing, but with modern styling, incorporating stainless steel exhaust tailpipes, also provides excellent engine room hot air discharge facilities well above upper deck levels, and as the exhaust system is in weather tight enclosures the longevity of the entire system is beyond question, and to date to our knowledge, Watson series existing vessels have not been in need of exhaust system maintenance.

In terms of disadvantages of a “dry stack” system we have identified two only but which we believe can be readily addressed.

Firstly, on engine “start up” at times, a “sooty” discharge may occur, leaving soot deposits on decks etc. However with Pacific Motoryachts arrangement of high level exhaust discharge pipes this is greatly minimized. Also it is becoming a non-issue now with the new tier II E.P.A certified engines which are free of such emissions.

Secondly, exhaust noise emissions. Again, with Pacific Motoryachts high level exhaust pipe design, coupled with very efficient technically advanced silencers as sourced and selected to meet the high standards set, will, we consider satisfy the most stringent owner criteria.

Last Updated (Wednesday, 15 September 2010 09:28)