Exhaust Elbow

[Harrier]

I am in the process of replacing the exhaust elbow on my Westerbeke 20B.  The equipment being removed is galvanized steel pipe and goes through ~6" rise after exiting the manifold before returning to the muffler.  I purchased a OEM Westerbeke 45degree down elbow (no riser) to replace the current arrangement, but am second guessing the installation.  It appears to meet specs for height above the waterline, etc but I'm now wondering if the riser is critical to preventing risk of flooding the engine.  Has anyone installed this type of exhaust, or know if the riser is required?  Thanks 

[wes]

Very interesting question! I've been staring anxiously at the original 1988 exhaust elbow on my Universal M12, wondering how hard I'll have to work to get it off and replace it (soon). Like yours, it has the vertical riser. I've just assumed that's to get it as high above the waterline as possible, but I don't really know.

Wes

[brackish]

I'm reminded of something that happened a long time ago with regard to cooling systems, risers and exhaust mufflers and thought I'd pass it on.  Our Columbia 8.7 was approximately 20 years old when we started to get water in the aft most cylinder of the Universal Atomic four and it was happening on shutdown of the motor.  We struggled for a while trying to figure out what was causing it.  I finally contacted Moyer Marine, the guru of all things atomic four to ask an opinion.  He didn't know but sent me a package of articles on cooling exhaust systems to see if I could find something in there. Turns out as scale builds up over time in the water muffler it takes up room required for the water to drop down when the motor is shut down and the water pump stops.  The design is such that the water is supposed to drop down into the water muffler.  Because, displaced by the volume of the scale, there was no place for it to go it backed up and went back to the exhaust valve on the last cylinder and got in the cylinder. Don't ask me about the capacity geometry of the paths, I never figured it out, however, we pulled the muffler, cleaned it out and problem was solved.  Just for info, hope it might help someone who has a similar problem.

[Harrier]

Wes, definitely recommend replacement before you "need it".  Mine fractured (fortunately not catastrophically) and ended up spraying the engine compartment and lockers with a nice fine mist of salt water and diesel soot.  Took an entire day just to clean everything.  Brackish notes another potential failure mode.  Removing the elbow was actually very straightforward.  Its only attached to the exhaust manifold via a v-band style hose clamp.  I decided to make the job bigger by removing all coolant hoses for replacement as well as the heat exchanger for deep clean and fresh paint.  If you are just doing the elbow, its probably not much than an hour of work.
The riser undoubtedly adds height above the waterline, and in this regard, I guess more is better.  But, I tend to appreciate form as much as function, and liked the idea of a more 'elegant' elbow design.  That said, I obviously dont want to risk flooding the engine.  Function first. 

Anyway, thanks for the input. 

[wes]

Yep, I'm worrying about that heat exchanger too. It's already been repaired once (brazed) for a pinhole leak at one of the hose nipples.

I did replace every hose (including exhaust hoses) when I bought the boat. Cheap insurance.

Wes

[Harrier]

Spoke with Gerry at Compac Yachts.  He confirmed that the original riser was just a fabrication of standard galvanized NPT pipe fittings.  The only piece they fabricated was the water injection nipple which is welded to the NPT.  He offered to sell that piece for ~$65. 
Regarding the ?need? for the riser, he seemed less certain that it was required, but recommended the general good practice of taking advantage of all available height under the deck. 
Also after reviewing several articles on the subject, I?ve come to appreciate the added safety of inserting water down stream of the high point.  The cast housing manufactured by westerbeke and others injects water directly adjacent to the manifold.  The water travels through an internal plenum cooling the entire elbow, and ultimately mixes with the exhaust down stream similar to the fabrication. The potential issue is that if the internal plenum where to ever crack, you run the risk of pumping water into the manifold and engine.  Opposed to the fabrication, you just make a mess of your engine compartment - like as happened to me?

[Harrier]

Sorry, one more thing.  If you are not able to remove the V clamp exhaust manifold adapter from the old piping (mine is soaking in in pb blaster but hasn?t budged yet), you will need to purchase a new one from westerbeke.  Best price I?ve found so far is $90.