Thoughts on using ABS pipe for an exhaust gooseneck

[briblack]

exhaust temperature can rise rapidly if the water injection stops for any reason. exhaust system components are always(?) fire resistant, even if they're hose or fiberglass. (mufflers, elbows). I think ABS can burn, and wouldn't be comfortable with ABS on my boat.

[Boatwright]

Yikes! The injection point for cooling water is at the goose-neck, that is why they are called injection elbows and that is also why they are made of metal. Downstream, after cooling water has been injected the exhaust is no hotter than boiling water, so there plastic is OK.

The Yanmar elbows are available, although US parts suppliers charge way too much. Several years ago, I got one on eBay for a reasonable price.

It is possible to fabricate one from pipe fittings, although it will not have the internal baffle on the OEM part. Google the topic. A fitting for the water will have to be welded or brazed into the setup. You also need to know that Japanese pipe (JIC) threads are NOT the same as US threads (NPT). Japanese threads however are the same as British threads. British thread pipe fittings are available from McMaster-Carr.

If you decide to use plastic get ready to jump overboard when your boat catches fire.

[Vince124]

Originally Posted by Boatwright

Yikes! The injection point for cooling water is at the goose-neck, that is why they are called injection elbows and that is also why they are made of metal. Downstream, after cooling water has been injected the exhaust is no hotter than boiling water, so there plastic is OK.

The Yanmar elbows are available, although US parts suppliers charge way too much. Several years ago, I got one on eBay for a reasonable price.

It is possible to fabricate one from pipe fittings, although it will not have the internal baffle on the OEM part. Google the topic. A fitting for the water will have to be welded or brazed into the setup. You also need to know that Japanese pipe (JIC) threads are NOT the same as US threads (NPT). Japanese threads however are the same as British threads. British thread pipe fittings are available from McMaster-Carr.

If you decide to use plastic get ready to jump overboard when your boat catches fire.

The injection point for cooling water is at the goose-neck? You do realize that a gooseneck and an injection elbow are different things right? The gooseneck (a.k.a. swan neck) in this case is at the transom, while the injection elbow is at engine.

For all of you naysayers on ABS, please let me know why Vetus has been making their waterlock mufflers and goosenecks out of plastic for years.

[blubaju]

Since 30 years: mixing Elbow stainless, connection hose to water collector (=muffler) hydraulic rubber hose, everything else downstream PVC, it is all cold down there. Forget metal, it corrodes, more or less, but it does

[kev_rm]

Originally Posted by briblack

exhaust temperature can rise rapidly if the water injection stops for any reason. exhaust system components are always(?) fire resistant, even if they're hose or fiberglass. (mufflers, elbows). I think ABS can burn, and wouldn't be comfortable with ABS on my boat.

Uh ya, this. It might be cool when your impeller is intact but it will be 250 degrees in a hurry when its not.

[thunderhoof]

Let's hope the water intake or the filter never gets plugged or that the impeller of the raw water pump never fails. In any of these cases the hot exhaust could put a hole in ABS or PVC pipe before your overtemp alarm sounds.

[Compass790]

Originally Posted by thunderhoof

Let's hope the water intake or the filter never gets plugged or that the impeller of the raw water pump never fails. In any of these cases the hot exhaust could put a hole in ABS or PVC pipe before your overtemp alarm sounds.

This hasn't been my experience. Had the water temp alarm go off more than a few times when motorsailing & heeled over too far so water intake comes out & it has never melted our PVC pipe or plastic waterlock muffler. Our system goes ss 316L mixing elbow,steam condensate hose ( like exhaust hose but free) pvc pipe, water lock muffler, pvc pipe, steam condensate hose in a loop then ss 316 stern outlet.

However happy to confess have melted a previous plastic waterlock muffler on a boat with no alarm in the exhaust when impeller failed. It was an air-cooled diesel so no engine alarm. The muffler never caught fire, simply melted & it's pretty quickly apparent when exhaust fumes start coming out of the cabin what is happening

If you have a high horsepower turbo diesel maybe it would happen but my advice was to the OP with his 1GM10 Yanmar with a very similar heatload to our YSM8. I would not comment on it ( without caveats) if I wasn't confident it would be a goer. Have made a few ss exhaust systems out of both tube & pipe, purged & not purged & prefer plastic in its various forms,FRP/GRP where it is possible to use it on the small diesels I'm used to.

As stated in my previous post you need to have a working overtemp alarm

As for the vibration aspect if you isolate the pvc/abs with some exhaust hose that should take care of that. Havent seen many engines that vibrate more than our 8hp single & we dont have much exhaust hose between the ss injection elbow & the PVC pipe.

My conclusion is, forget the naysayers & install the abs, you'll be fine. That's it for me on this thread

[qwert]

I think (note think ) that the Vetus fittings are made of polypropylene which has a no of varieties but the melting point is around 150-160degC.

The majority of waterlocks made by a several different vendors are plastic and they come before the gooseneck. Subject to the fatigue possibilities mentioned earlier I think you'd be fine but if I was doing it I'd be installing a thermocouple in the exhaust a short distance after the water comes into it. This will give you warning of a dangerous increase in temp.

Note that ABS is the principal plastic used in vacuum forming because it becomes flexible at a relatively low temp.

As an aside an exhaust temp warning is arguably better than an engine temp gauge because the moment your cooling water is restricted the exhaust heats up and you have several minutes before the engine starts to sustain damage (impeller excluded). If you react to an engine overheat gauge you have to shut it down immediately.

[Djarraluda]

Use of 316l stainless at high temp is a waste of money. At elevated temps it corrodes just like mild steel. If you want a high temp corrosion resisting material, you need a Duplex stainless steel, but it is not cheap! The material to avoid is copper
Roger

[Vince124]

Originally Posted by Compass790

My conclusion is, forget the naysayers & install the abs, you'll be fine. That's it for me on this thread

Thanks Compass. I've actually been using it for testing the engine on the hard for several hours at least and the exhaust has been surprisingly cool.


What most people probably don't realize is that high temp rubber wet-exhaust hose has a lower melting point than you'd think. Typically 138 degrees C or less.

[Jim Cate]

The material to avoid is copper

At it's current price copper isn't a likely choice, but I'm curious as to why you say this?

Jim

[Reefmagnet]

Originally Posted by Vince124

The injection point for cooling water is at the goose-neck? You do realize that a gooseneck and an injection elbow are different things right? The gooseneck (a.k.a. swan neck) in this case is at the transom, while the injection elbow is at engine.

For all of you naysayers on ABS, please let me know why Vetus has been making their waterlock mufflers and goosenecks out of plastic for years.

Your water muffler easily won't sink the boat if it fails. A goose neck has a lot higher probability.

A 180 degree stainless steel exhaust bend would probably make a cheap alternative goose neck.

[Cliffhanger]

Technically you are right, amorpous plastics like PVC don't melt. Unlike semi-crystaline plastics. But at 240 deg C, PVC will have the consisancy of thick honey, which in layman's terms is pretty much "melted." So, for amorphous plastics like PVC, the glass transition temp (i.e. the temp at which it will soften and deform) is what is important and for PVC it is around 85 deg C - roughly the coolant temp. Of course under normal conditions, the raw water temp will be well below that.

The questions I would ask myself is "how confident am I that the raw water temp will never get to 85 deg C?" and "if it did, what would happen?"

At the glass transition temp, the pipe would act like a flexible hose instead of a rigid pipe, it wouldn't necessarily leak. But for example if there was a hose clamp relying on the dimensional stability of a rigid pipe that has now become a flexible hose, I think you might have problems.

[saillr]

I bought a fiberglass exhaust elbow from "Fisheries Supply" in Seattle WA over 30 years ago. It was to raise the exhaust loop to deck level and is on a Yanmar 4JH2E. Has worked fine now for 30 years and still is fine.

[Davo1404]

Hi Vince
I have the same home built plastic goose neck exhaust riser in the stern locker exiting above the waterline. Been there for 20 years. Engine is a 2GM20F with about a 6 ft exhaust hose run from the plastic water lock.