Today I’m documenting the final step of the major exhaust system work: yanking out the old system. While it might seem like I’m jumping around unfocused, messing with the exhaust before the hull is painted, the simple fact is that I don’t want to cut, grind, drill or use epoxy resin around anything that’s already painted with “the shiny.” The exhaust system had to be done before we put the last coat of Awlgrip 545 primer on the hull. If the mechanic I fired in July 2013 had installed the engines as promised back in September 2012, I wouldn’t be dealing with this now.
The OE exhaust system consisted of two 15-foot sections of 5-inch Schedule 40 pipes welded in from the transom to the engine room bulkhead. Inside the ER, there were two large steel “suitcase” mufflers, all of which had pretty much rotted out after 15 years of service. When we got the boat in 2007, she’d been on the hard since the mid-’80s. She’d only been running on the water for a decade and a half before ending up on purgatory row. So, rather than just go with the exhaust system that Chris Craft used, which obviously had its shortcomings, I wanted to do something better, longer lasting, and quieter. The factors that led me to go with side exhaust and waterlift mufflers were:
Noise reduction–I’ve always had Detroit-powered boats and the sound of the exhaust was something I used to like…but not for long days at the helm. Even my other boat–a 1968 427 Ford-powered Commander 42–sounds wonderful…for about 15 minutes. After that it’s pretty much just noise. Granted, the Cummins 6CTAs in the Roamer will be a lot quieter than Detroits, but they’re hardly quiet. The waterlift mufflers are going to make for a quiet ride. In solving one problem though, another pops up.
Backpressure–I’d have to run 15 feet of 8″ pipe out the back on each side to get the backpressure where Cummins wants it. By going out the side and using an auxiliary raw water outlet so it doesn’t all have to go through the muffler, I can stick with a 6″ system and keep the backpressure down.
Space– the OE 5″ pipes took up roughly 12″ of width from each side of the aft stateroom. 8″ pipes would have pushed the wasted width to about 30 inches, and the pipes are 18 inches above the aft stateroom floors. When you add in air space around the pipes, you lose a huge amount of storage volume by running the exhaust out the transom. And finally,
Bang for the buck–the price delta between 6″ exhaust parts and 8″ is significant.
While taking out the old exhaust system, I found some more reasons why long aluminum pipes out the transom weren’t such a great idea.
In the pic above, you can see the “pipe within a pipe” consisting of the original 5″ exhaust pipe with the 3.5″ replacement I installed inside it for the Lehman 120 engines I originally planned to use for the boat. Let me know if anybody’s interested in some nearly new 3.5″ 6061 aluminum pipe…or some Lehman 120s with Twin Disc MG-502 gears.
One very nice thing about aluminum is that you can use common woodworking tools to cut it. I do find, though, that metal cutting jigsaw blades last longer than ones intended for wood.
My Miller Trailblazer 280 and Spoolmatic 30A worked real well for welding the patches in.
I used a carbide blade on my beater Skilsaw to make the initial cuts to get the pipe down to a manageable size, since carbide cuts through aluminum like a hot knife through butter. Then I followed up with my Harbor Freight sawsall to finish the cuts. The HF saw is noisy, but what do you expect for $20? With good Freud blades it does a good enough job and is still going strong after 7 years.
Incidentally, the pic above shows the half of the pipe that’s still connected to the boat at the engine room bulkhead. It’s also connected to the hull frame at the cut point. Since that welded brace midway along the pipe is behind extensive cabinetry with the original interior and the OE fuel tank, it’s got to be a really big job gaining access if you ever have to…say…replace a rotten pipe. You can’t just cut the two ends and pull the pipe out the transom.
The shot above shows the interior of the exhaust pipe that was welded to the ER bulkhead. The pipe is rotated so what was the bottom is on the right side in the pic. You can see the extensive pitting in the metal, especially where raw water would have been flowing when the engines were running. My theory is that the aluminum was attacked by copper ions from the exhaust risers on the Super Seamaster twin turbo engines that I pulled out of the boat back in 2008. Some of those pits looked extremely deep…
Like the rest of the hull, Chris Craft coated the exterior of the exhaust pipes with bitumastic and silver paint. Out of curiosity, I looked at the outside and noticed three spots where there was a wee bit of white powder, AKA aluminum oxide, which is what aluminum turns into when it corrodes.
My steel pick when straight through the pipe with very little effort. One of the holes was big enough to put a 1/4-20 bolt through it; another was big enough for a 3/16″ screw.
When I saw this I had to laugh, thinking back to the fellow who sold the boat to me when he said all it needs is engines and a paint job.
With the OE exhaust system off the boat and the new side exhaust flanges at the paint shop, I focused on wrapping up the final work to get the hull ready for “the shiny.”