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Replacing Exhaust again...need to get it right this time

7K views 24 replies 10 participants last post by  MarkSF 
#1 ·
The PO of my 1972 Northstar 38 re-powered it in 1992 with a new Universal M4-30. The exhaust setup consists of a riser where raw(salt) water cools the hot exhaust via a double-walled metal riser that's fastened to the exhaust manifold on one end and flanged to a DRY, wrapped, black-iron exhaust pipe. The water from the riser exits via fitting into a rubber hose which marries up with the dry exhaust pipe 12 fee away just before exiting at the stern.

The black-iron dry exhaust pipe failed in 2002, and after replacing it, is now failing again. The riser is just fine.

I'd like a longer-lasting solution because the dry pipe takes some tough turns and it's a very difficult, custom job to replace it. Access is very limited

I'm wondering if some of the newer Trident rubber hoses could take the place of the black iron. Or should I consider replacing the riser and black-iron pipe with a whole new setup, like a Vetus water-lock. I'm a bit scared of the water-muffler approach as I'd be inventing the new design and I'm worried about really botching it - as in, water back-feeding into the engine if I get it wrong.

Thoughts on either approach? or do you have an alternative?
 
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#2 ·
We replaced our old riser and stainless muffler with one of the new VETUS waterlock muffler and it has had great results in two years. Boat is substantially quieter at the exhaust.

Dave
 
#4 ·
Normally the water is injected just after the riser and it both cools the exhaust and makes the system quieter. Your 12' of dry exhaust is rare in a sailboat.

Rubber exhaust hose is designed for the water cooled section and will not work for the dry section of the exhaust.

Properly designed and with the desired (required I think) anti-siphon there is virtually no risk of flooding the engine.

Here is a Yanmar diagram showing their ideal layout, but it is not brand specific. The anti-siphon can be a small hose exiting in the cockpit well above a drain to act as a telltale so you know the cooling water is flowing.

Hope this helps.
 

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#5 ·
Agree that hose is only good after the water injection. It will melt.

My previous boat had a Universal 5411 and the exhaust system was standard black iron fittings and nipples for the loop, hose after the water injection, and a Vetus waterlock muffler. The black iron loop lasted 15 years and was very inexpensive to replace since the pieces were standard plumbing parts.
 
#6 ·
Mititempo and JimsCal, thank you. but i spent some time talking to silicone hose distributors. I haven't gotten to the actual manufacturer, but the distribution network challenges your conclusion: meltdown. They say, some of it, anyway, will withstand 500 degrees F. that's enough headroom to do what I need (I think).

Engineering question: if i measure the surface temp of the existing metal exhaust at the hottest point, just after the water-injected riser, and the black-iron reads, say, 300, how hot is the gas inside?
 
#7 · (Edited)
Hotter inside I would guess but I am not sure what temp.

Is your concern siphoning into the engine or offshore seas flooding the engine? Siphoning is taken care of with a layout like the Yanmar one I posted above. As sea it makes no difference, if the stern is clobbered with seas the engine will get wet unless a seacock is installed at the outlet.
 
#8 · (Edited)
Hmmm. The exhaust gases in a diesel running under full load that has reached equilibrium temperature exit the cylinder at 1500 to 2000 degrees. By the time it gets out of the manifold, I would wag a guess of 1000 - 1200 at the manifold exit, although less under more normal conditions. I would not trust any formulation of rubber to stand up to those kinds of temps. I expect it would melt and char from the inside out.

Concern over overheating when you are in nasty conditions and really need the engine is bad enough. Personally, I would not want to worry also about whether running my engine flat out for too long would do in my exhaust. How do you feel about cleaning charred rubber bits out of your water muffler?

Exhaust has corrosive gases. Chemical reactions happen faster as temperature goes up. You say your exhaust pipe was replaced in 2002 and you want to get it right? If this pipe lasted 9 years I would say you got it right last time and should do the same thing again.
 
#9 ·
Exhaust gas temperatures can be well in excess of 500F after operating at load for a period of time. dacap is correct in that gases leaving the cylinder are well in excess of 1000F. A lot depends on the construction of the water cooled exhaust manifold, but temps of 600 to 800F at the exhaust flange would not be out of the question. There is a reason why the section before water injection is commonly wrapped in high temperature insulation.
 
#12 ·
We have had over 25 years of experience with exhaust risers in Catalina 34s. Our skippers have made them out of a variety of materials. Black steel, galvanized (not recommended), and the factory makes them out of stainless steel. You might note that NONE of them includes flexible hose.

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The hump hose goes between the end of the riser and the muffler, after the water is added.
 
#13 · (Edited)
Thanks for all the input everyone. I will take some pictures and post as soon as I can work it out.

I know I'm pushing the issue against the advice above - at least in word, anyway. I really haven't made up my mind on the design.

Someone above asked what my concern was in installing a conventional setup using a water muffler. The reason for exploring alternatives is to avoid the added installation complexity and maybe cost. I'm not worried about the anti-siphon aspect per se, I'm more concerned about the unforeseen - things I might not realize I've done wrong while on the hard, but made painfully obvious under way. I heel my boat considerably and I worry about the concept of 'water line' as a result, for example.

So two more questions: 1) regarding operating temperature of exhaust gas: if I used an infrared thermometer and pointed it at the dry pipe (it's exterior that is) at it's hottest point, would that would give me an actual reading, right? I could even induce a near overheat by say, turning off the raw water intake. And of course, with a careful eye on the temp gauge, I could retake the temp on the pipe. Right?

And what about Stainless 'flex hose' such as this: http://www.jcwhitney.com/flexible-exhaust-tubing/p2006251.jcwx anyone care to weigh in on whether this might outlast the 9 year life of black-iron?

Thanks all!
 
#14 ·
It often amazes me why people try to reinvent the wheel and end up with something that's square.

Really, you have two separate sections: engine to muffler - should be solid pipe to the exhaust riser nipple where the water joins it, then hump hose to the muffler; muffler to exhaust point on the hull should be rated exhaust hose.

What's so hard?
 
#15 ·
Stu, I'm sure your tone is for my well being, not to berate me.
My motives are pure, I swear. I'm not a square wheel sort at all :)

Please read from the top. My current set-up is not what you state. I've got an inter-cooled double-walled heat-exchanger affixed right to my exhaust manifold. The exhaust pipe from that point to the stern is dry, heat-shield wrapped black-iron, as it has been since it was duplicated about 10 years ago.


I'm just trying to get the most value for the buck. That is, I want to fix this only one more time and not have to fix it again until after I'm dead or after I've sold the boat - at least twenty or thirty years if possible. My next two criteria in order of importance are, ease of installation and cost.

More constructive commentary welcome! :p
 
#18 ·
The PO of my 1972 Northstar 38 re-powered it in 1992 with a new Universal M4-30.

Or should I consider replacing the riser and black-iron pipe with a whole new setup, like a Vetus water-lock. I'm a bit scared of the water-muffler approach as I'd be inventing the new design and I'm worried about really botching it - as in, water back-feeding into the engine if I get it wrong.

Thoughts on either approach? or do you have an alternative?
Not berating, just trying to simplify, based on your first post. That double walled contraption is just more difficult to deal with, which is why I believe both Brian and I have suggested a simpler approach. As you yourself mentioned in your first post. That's all.
 
#19 ·
Pub, a couple of thoughts on your search for a better solution.

Any kind of "flex" pipe that is not smoothwalled inside (which means almost all of them) is going to be an exhaust restriction in itself. Flex pipe is only used as a kludge, mainly for that reason and inferior strength.

And while I've bought from what is lovingly called "JC Sh*tney" because sometimes they have things no one else has, their quality has never been their raison d'etre. I wouldn't buy parachute harness fittings from them even if there was no other source. Think of them as, well, Harbor Freight without all the local stores.

Engine exhaust temps are also without any doubt going to be in the range of 1000F+ during normal operation. No matter what your thermometer says on the outside--it is going to be a minimum of 700F on the inside, which is why there's an emphasis on using cooling water as close to the engine as you can. If for any reason you have a cooling water failure and your exhaust pipe can't handle a thousand degrees, you're going to have a bigger problem. So by all means, silicone hose or exhaust hose--just make Real Damn Sure your cooling flow is going to be 100% adequate 100% of the time with 100% coverage in there.
Black iron pipe comes in different wall thicknesses IIRC, maybe you can get better life just by going to a heavier wall pipe?
I'd like a dry exhaust vented up the mast, personally. (VBG)
 
#21 ·
I still don't think it makes sense to replace an inferior system with the same type. Below is a pic of a Beta 25 engine showing the outlet and the water injection point (from Northern Yacht Restoration). From the outlet to the stern it is water cooled exhaust hose to the waterlift muffler, a much safer alternative. I wouldn't want a long run of hot exhaust pipe to the stern from the engine.
 

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