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Oceanis 351 Exhaust Question

Dec 7, 2016
2
Beneteau Oceanis 351 Beaufort, NC
Due to corrosion, leading to water leaking, I just disassembled the water exhaust from the heat exchanger on my 1994 Oceanis 351. The engine is a Perkins M30 29 hp diesel. The exhaust elbow was completely corroded, and now I'm searching for a new one and have run into problems with parts.
It seems that the standard set up from the Perkins engine is for the raw water cover to hook up directly to an inlet on the exhaust elbow. However, on the Beneteau the raw water cover and the exhaust elbow separately connect to a big exhaust manifold pipe/tub thing that connects to the muffler. I've attempted to attach a pic of that part. The small inlet facing out is the raw water inlet. The "J" portion is the heat exchange exhaust, and the part with the ring clamps goes to the muffler / water exhaust.
Beneteau water exhaust.jpg

I can't find any reference to this part anywhere. It seems like all the pics I find online have the raw water going directly into the exhaust elbow, and then out. If I rebuild it, can I just get a replacement exhaust elbow with an inlet to run the raw water right into it? Can I omit this whole beast and simplify?
 

DougM

.
Jul 24, 2005
2,102
Beneteau 323 Manistee, MI
Not familiar with the Perkins. Nevertheless, that does not look like an original equipment exhaust elbow setup. Are you sure that is not something that was cobbled together by a previous owner? That could be why you cannot locate anything like it.
 
Nov 23, 2009
437
Beneteau Oceanis 361 Clipper --
I really try to understand what this photo is! I have the Volvo MD2030 engine which is in fact the Perkins M30 but painted green (it's even mentioned on the engine that it's Perkins). There's a simple mixing elbow somewhere at the rear of the engine. The top part is connected with the heat exchanger (for raw water) and there's a black hose/pipe that connects it to the muffler. Nothing complicated. Probably as Doug mentioned is something a previous owner did and you should simply instal the "proper" one.
 
Dec 7, 2016
2
Beneteau Oceanis 351 Beaufort, NC
I really try to understand what this photo is! I have the Volvo MD2030 engine which is in fact the Perkins M30 but painted green (it's even mentioned on the engine that it's Perkins). There's a simple mixing elbow somewhere at the rear of the engine. The top part is connected with the heat exchanger (for raw water) and there's a black hose/pipe that connects it to the muffler. Nothing complicated. Probably as Doug mentioned is something a previous owner did and you should simply instal the "proper" one.
The photo rotated when I posted it. It is rotated 90 deg clockwise. So the "loop" you see at 3 o'clock, when mounted, is actually up. The exhaust elbow connects to this thing at the part that is at 6 o'clock in the photo. Connection at 9 o'clock leads to the muffler. Connection pointing straight out at you is the raw water inlet. The "steel tape" you see at the loop is mine: the whole reason I yanked it out is that the mounting bolt eroded through while going down the ICW, blowing exhaust and sea water into my engine compartment. So the tape was a field expedient patch (which held up for the next two years, I'll add!). Now, however, I was getting a lot of exhaust leaking from the point where the exhaust elbow itself was corroded, which is why I pulled this all out.

I would think the same thing (that it was an owner modification), except that it was actually attached via a bolt to a mounting frame that is integral to the engine installation. I looked at that mount to see if it looked welded in after the fact, and it looks for all the world like it was mounted with the engine (which is original). I've also looked at the "typical" mixing elbows, and the way they angle downward would look like trouble actually fitting in this particular install. Really makes me wonder if this was a Beneteau factory modification to make the engine fit in this particular model. The way it fits, it is almost mandatory that the exhaust exits, then takes a turn upwards. This would be the reason that the water inlet needed to be on the "down side" of the loop. I also wonder if they designed this upwards facing loop to act as a defense against backflow.

Having said that, there is some degree of modification, as it leads out to a plastic water lift muffler that is clearly not original. I have most of the original documents / owner's manuals, and there is no diagram that specifically shows the exhaust set up for this particular boat.
My problem right now is that the iron portion of the exhaust elbow is so corroded and so hard to get to, that I'm having a great deal of trouble getting it off the exchanger. I suspect, once I get it off, I'm going to need to get a custom build. Good times.
 
Nov 6, 2006
9,107
Hunter 34 Mandeville Louisiana
Any industrial pipe shop could fab that for you, or you could make an equivalent from a Yanmar or other elbow.. if Yanmar, you'd have to deal with the left threads in the ell.. You can make one yourself from regular pipe fittings threaded together.. The important things are, 1. that the water come in where it can't get back into the engine and, 2. the height of the elbow above the engine must stay the same so that water cannot get back into the engine.
 
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Nov 23, 2009
437
Beneteau Oceanis 361 Clipper --
I think (from your description) what you have is what volvo calls an exhaust riser.

Edit: See the attachment. Two options. The usual one and the one with the riser.
 

Attachments

Last edited:
Mar 20, 2016
461
Beneteau 351 WYC Whitby
I don't think its a modification, I have a 94 351 and it looks the same
 
Mar 20, 2016
461
Beneteau 351 WYC Whitby
Any industrial pipe shop could fab that for you, or you could make an equivalent from a Yanmar or other elbow.. if Yanmar, you'd have to deal with the left threads in the ell.. You can make one yourself from regular pipe fittings threaded together.. The important things are, 1. that the water come in where it can't get back into the engine and, 2. the height of the elbow above the engine must stay the same so that water cannot get back into the engine.
I like this idea , you could order 316 stainless fittings from McMaster Carr thread them together and make this pipe up. Only a flange may have to be fabricated to attach at the exchanger. Then wrap in exhaust wrap from speed shop to insulate, it will last forever
 
Mar 20, 2016
461
Beneteau 351 WYC Whitby
I have the same setup had the boat for 5 years , if its not broken I would leave it. If mine went ,I would not use the standard mixing elbow ,because it most likely falls below the water line that's why they went high before injecting the water. The mixing style like on the md2030 have the tendency to plug because of narrow passage to inject water down and they don't go high. I don't think this has the narrow passage to plug. I would thread together 316, 2 inch pipe using 4x 90 degree 1x 45degree and a 2inch TEE x 3/4 where the water injects using different lengths of nipples to make it the same. 90 off plate ,then 45 to kick it back , then 90 up 2x90 to bring it down , then tee and a 2 inch barb to push the hose onto.
The plate that bolts to the exhaust can be fabricated out of 316 plate tapped for 2 inch, thread in a close nipple to attach to first 90 and weld the plate to the nipple. Now it's pretty much for life.
Or maybe you can get away with the standard S/S exhaust mixer , however the engineers went high for a reason ,get water back into the engine ,hydraulic lock and bend the connecting rods or worse and bring your wallet
 
Dec 31, 2016
319
Beneteau Oceanis 351 Charlottetown
Here's what mine looked like under the heat wrap,. They were made from thin wall copper tubing, silver soldered together with a stainless steel flange. I would assume most that are is salt water will look the same once the cover is removed. Keep in mind these are unavailable now.
 

Attachments

Feb 7, 2010
15
Beneteau Oceanis 351 Rockport,Tx
Not familiar with the Perkins. Nevertheless, that does not look like an original equipment exhaust elbow setup. Are you sure that is not something that was cobbled together by a previous owner? That could be why you cannot locate anything like it.
It is exactly the same on my 95 351. I had one custom-made for a replacement