For our engine replacement, the only exhaust options that Beta Marine offers will not fit into the space available on the Catalina 36, so the only option is to build your own. At first, I considered reusing most of the existing exhaust, since it was nearly new. However, the Beta rep said the exhaust had to be 2″ (50cm) all the way in order to meet the back pressure specs. If we chose to ignore that, it could void the warrantee. Therefore, I rebuilt the entire exhaust system.
While it was on the hard for other work, I had the exhaust through-hull replaced with one that could accommodate a 2″ hose. I also ordered a new water-lock muffler from Catalina direct. I had them use the same footprint and design as the standard one for Catalina 36, but replace the two inlet/outlet to accept 2″ hose instead of the standard 1 5/8″.
For the exhaust riser, I started with the “dry exhaust” flange from Beta Marine. It is really just a mounting plate attached to a 1.5″ pipe thread. This would allow me to use standard pipe to build the riser, and easily adjust the angles to get the fit right. I chose to use stainless steel pipe and have a custom injection nipple made.
The metal shop I used specializes in marine applications, and they said I could use schedule-40 304 stainless pipe instead of the schedule-80 316 I had planned on. Since the pipe is all on the dry side of the exhaust, they claimed the cheaper pipe would work just fine and still last a very long time. They then built the injection nipple using a combination of 1.5″ pipe, 3/4″ pipe, and a piece of 2″ OD pipe. I needed the water injection to exit horizontally to allow the hoses to fit in the space, but I didn’t want any chance of the water splashing up into the riser, so they curved the inlet pipe, and inserted it into the exhaust stream headed downward.
Before wrapping
After wrapping
As you can see in the photos above, I also rerouted the cooling water lines, and reinstalled the exhaust temp alarm sensor on the hump hose.
