Exhaust elbows

[Steve_N]

One of the problems with elbows is the water is injected one side and in the past some have eroded at the bend where the exhaust flow drives the water against one point on the inside. Don't know if S/S is going to have the same problem, but Mermaid S/S elbow for my Ford injects the water into a collar surrounding the exhaust pipe, the flexi fits outside the collar.

I though that may be the weak point on my home-made (supposedly temporary) stainless riser on my MD21B. For simplicity's sake I kept it single skin and the cooling water enters directly through the single wall at 90 degrees, but after approaching 300 hours there's no sign of any corrosion at all. It's SS316 at that point.

 

[jwilson]

The Yanmar ones have the same design. The failure mode on these is not corrosion, it is fatigue. Mine is explained at the bottom of this page http://coxeng.co.uk/metallurgy/fatigue/

I agree that fatigue is probably part of the problem with Yanmar ones. Mine (3YM) though not that old sheared at the weld this summer after a charterer got a big mooring warp round the prop and stalled the engine, torqueing it on it's mounts. It also bent bolts on the drive coupling. I was expecting to find at least one of the engine rubber mounts broken too, but they were OK.

In the ancient law of escalating problems, the exhaust water spraying around the engine compartment soaked the foam air filter element, which made the engine run slow and ultra-rich, hence black smoke plus salt water in the engine space. A week afterwards the engine (which previously had been smart silver, started to develop rust stains on the block and ancillaries, despite liberal WD40.

 

[JumbleDuck]

I agree that fatigue is probably part of the problem with Yanmar ones.

I was never happy about the three-point mounting - it might have been OK if the three bolts were equally space ~120^o apart, but 90^o/ 90^o/ 180^o is asking for trouble.

 

[Tim O]

Im after a new elbow for my Beta 38...curent one has tiny holes developing.

Any suggestions for a fabricator in or around Cardiff or South Wales area?