Exhausted

Probably more than you ever wanted to know about exhaust systems.

Ode to an Exhaust Pipe
“Old little pipe in the stern,
expelling gases engines burn.
Nobody pays you much ado, 
except for an occasional “PU”. 

Well, friends, I have really hit bottom this time.  Poetry and an entire article on exhaust systems for God’s sake. But wait! Some exhaust systems were very special and need to be remembered. Sadly, technology has driven most modern exhaust systems underwater where they are unseen and hardly heard.  

The Rise and Fall of Exhaust Pipes

Around the turn of the century when gasoline engines were first dropped into blowboat hulls producing the first powerboats, the products of combustion – exhaust gases – needed to be routed from the engine compartment to atmosphere. On the earliest double-ended gasoline vessels, this was easily accomplished by simply running a pipe from the engine through the hull side. The huge, slow turning engines of the day produced a very slow pop… pop… pop… pop… one could literally count every explosion – even at full speed.  As engines became lighter, higher revving and more sophisticated, so did the exhaust systems.  Gases were usually led to the lower, outboard corners of a flat transom – not to the hull sides, not underwater, and certainly not through a dry stack.  Exhausts through the transom dumped into the low-pressure area created behind the vessel as she moved through the water. 

All the books tell you that, to protect the engine, exhaust systems should have a constant ½” per foot declivity from the point where the water is injected into the pipe to the discharge port. There are many different ways to set exhaust pipes in transoms.  Most popular was a simple cast bronze fitting screwed to the transom from the outside with a cast in nipple that penetrated the transom for fitting of a hose on the inside.  This was a very practical, straightforward (and very boring) approach to exhausts in transoms.   These systems, which carried on virtually unchanged for about 50 years, produced dull, monotonous, sounding and looking exhaust systems.  

Sooty Transoms

Before 1960, most medium sized pleasure boats were gasoline powered.  With the advent of diesel engines, however, everything changed. Diesel exhaust out the transom produced thick, black soot on the aft end of the vessel, which dictated alternative exhaust systems.  Diesel exhausts were first directed out the topsides just forward of the transom in an effort to get the gases into the slipstream around the hull. Transoms look absolutely naked without exhaust pipes on their lower outboard corners and I have never gotten used to this.  Then, underwater exhaust systems were developed directing the main exhaust through the bottom of the boat into the water and carrying it well aft in the wake before it surfaced.  These systems are effective, efficient and quiet (and also extremely boring).  While most of the exhaust systems we design today are of the underwater variety and extremely practical, it just is not the same.  

Many “Hot Dog” gasoline powered vessels these days use unmuffled straight exhaust pipes out the transom.  Big block, V8 gasoline engines produce an absolute assault on the senses and should be muffled or banned from our waterways (along with PWC and puffboats that never raise their sails).  These boorish, obnoxious, no class exhaust systems usually are a good match for the gold-chained set that owns these boats.  But there was a time when…

Maritime Symphony

The ultimate, nee plus ultra marine exhaust system of all time was fitted to most Chris-Craft cruisers in the late 40’s and 50’s.  Forget Handel’s water music – these exhausts were truly a stereo maritime symphony – gear head delights – works of art never again duplicated.  I do not believe Chris- Craft planned things this way but was the happy benefactor of circumstance.  Let me try to describe this incredible system.  Chris-Craft transoms of the day were things of rare beauty with a jaunty aft rake in profile and a generous radius in plan view.  Built of mahogany and highly varnished with bright stainless-steel trim where the topside planking met the transom, these sterns were absolute works of art. On most of their boats over 30-feet, twin pipes adorned the transom with flair.  

Chris-Craft did it right with large diameter copper tubes penetrating the transom with bronze trim rings. While these pipes could have arbitrarily been cut off plumb, they were elegantly and artistically cut to follow the rake and radius of the transom.  Yes, someone in the design department took the time to lay out exactly how these pipes would be cut. Chris-Craft exhaust pipes just looked right.  But it is the arresting sound and visual entertainment produced by these pipes, that, I believe came about by happenstance.  On those boats, engines were usually mounted well forward, low in the hull to allow the sleek, rakish superstructures of the day.  It was therefore necessary for the exhaust pipes to rise from the engine to the transom – ½” declivity be damned. This meant that water would collect in the low part of the pipes just aft of the engine when the engines were shut down or when they were idling.  Huge cast iron in line mufflers were usually fitted.

Let the Show Begin

When Chris-Craft engines were lit off, it was showtime! Eerily, out of the pipes – like water through a dam – came huge gushers of water without any exhaust sound whatsoever – the result of exhaust gases pushing the trapped water out of the pipes.  When the water cleared, the engines produced a mellow, throaty moan. Think of roaring lions on the Kalahari. Think of the sounds of Fords and Chevys of the same era fitted with glasspack mufflers augmented to the power of three. The exhaust moan would momentarily stop, interrupted by geysers of water from the pipes as it collected and was forced out by exhaust gases. As a kid in the 50’s, I could sit by the transom of a Chris-Craft and listen all day (It really doesn’t take much to entertain me).  At higher throttle settings, exhaust pressure was such that the pulsation stopped but the moan remained. 

Honorable mention for exhaust pipes of the day must go to Matthews, the famous builder from Port Clinton, Ohio. While the exhausts did not sound as great or pulse like Chris- Craft’s, they did come up with a unique exhaust pipe designed to direct the exhaust gas outboard into the slipstream of air passing the hull.  These unique pipes were round as they exited of the transom but then squeezed into sexy, narrow horizontal ovals angled outboard.  I do not know if they worked but they sure did look cool.  

Does anybody else in the world care about this kind of thing or it is just me? 

I am a guy who, immediately after taking delivery of a new C5 Corvette, tore out the stock exhaust system and installed, at great cost, a beautiful, stainless steel aftermarket system because the stock system just did not look nor sound “right.” 

When we initiate a custom design, our clients usually produce a long list of requirements. Never have I seen the words: “must sound like an old Chris-Craft.” But I can dream, can’t I?

(Reprinted with permission of Regina Fexas.)

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