can wet exhaust be reduced

[Terra Nova]

Originally Posted by jimbunyard

...I'd match the ID of the exhaust manifold outlet to the ID of the muffler inlet ID...

Originally Posted by jimbunyard

...Yanmar certainly has looked at your specific boat, application and financial situation, all the time keeping in mind that your personal satisfaction is paramount to their business model...

Ridiculous.

Any boat mechanic with a basic knowledge of engines will know that you match the OD of the mixing elbow outlet to the OD of the water lift muffler inlet. That gives you the ID of the exhaust hose.

OP--on your steel hull it is a very simple and inexpensive matter to remove the 2" exhaust fitting and substitute the correct 3" fitting.

[jimbunyard]

Originally Posted by Terra Nova

Ridiculous.

Any boat mechanic with a basic knowledge of engines will know that you match the OD of the mixing elbow outlet to the OD of the water lift muffler inlet. That gives you the ID of the exhaust hose.

OP--on your steel hull it is a very simple and inexpensive matter to remove the 2" exhaust fitting and substitute the correct 3" fitting.

What is truly ridiculous is the number of people who either cannot comprehend the original question, or, for whatever unfathomable reason, chose to mislead others, nefariously or otherwise...

mass flow rate = density of fluid x area of passage x velocity of flow

And, since we're talking about the flow rate through a round pipe, the 'area of passage' means the internal diameter of the pipe, because area = 3.14 x radius (1/2 the ID) squared.


__________

Using this 'logic' (within the context of the OP's question)

"...the OD of the mixing elbow outlet...the OD of the water lift muffler inlet... gives you the ID of the exhaust hose."

this


has exactly the same flow characteristics and capabilities as this.



________


Sooo, once again, it is very likely that, if the ID of the exhaust manifold outlet is 2 inches where it leaves the manifold (not the 'bell' of the mixing elbow), the existing hull outlet will work just fine, thereby saving the extra costs involved in removing and refitting a new outlet, as well as the extra costs for the larger muffler, hose and fittings. Savings are also realized by reduction of area taken up by having an oversized exhaust system...


And, if the OP needs a 'professional' and 'expert' opinion, maybe he can get ahold of Tony Athens at Seaboard Marine, (805) 382-6287. Tony'd likely be able to answer the question in very short order, as well as supply the parts necessary to complete the installation...

[Lepke]

All the technical crap aside, the more back pressure, the more effort your engine has to expend exhausting the spent charges from each cylinder. In your case you'd use slightly more fuel.
I use to do sprint car race engines, and just about every type of piston engine from aircraft to ship diesels. I got to see on a dyno the effect of the exhaust system. Most of the issue of back pressure happens at high rpm. 2-4 times higher rpm than almost any diesel. The article was written for hot roders and hobby racers working on a different set of issues. It's your boat, do what suits you best. The fuel cost on a sailboat is minimal anyway.
The amount of water going thru the exhaust can be changed, too. On bigger engines, it's common to send some of the raw water exhausted in a separate line, usually adjusted by some valves. You only need enough water in the exhaust line need for cooling the plumbing. That's how my boat is set up.

[a64pilot]

One of the Hunter models has I think a 2" exhaust with a Yanmar 4JHE engine, this does not meet warranty requirements of Yanmar, but was allowed for this installation.
The assumption is that if correctly run a 2" exhaust is OK, the issue may be correctly run, length, rise and number of restrictions as in direction changes I am sure makes a difference too.
I'd plumb it as is and measure the back pressure myself. I'd build myself a water manometer to measure it.

Even if you go with a three inch, it might be prudent to measure backpressure.

Quick Google found this
https://forums.sailboatowners.com/in...xhaust.155682/

[puffcard]

I would say no.
2" the area is 3.14 sqin
3" the area is 7.07 sqin

2" only has 44% of the area, that's a huge restriction. I would ask the manufacturer.

[jimbunyard]

Originally Posted by puffcard

I would say no.
2" the area is 3.14 sqin
3" the area is 7.07 sqin

2" only has 44% of the area, that's a huge restriction. I would ask the manufacturer.

Well, as 'they' say, "you can lead a horse to water...". Even though this is mostly rhetorical at this point (the OP hasn't made an entry in a week), we'll continue for posterity's sake...

Again;

mass flow rate = density of fluid x area of passage (internal diameter) x velocity of flow


And for those unfamiliar with the mixing elbow we're discussing here




The relevant dimension, the 50mm ID (1.9685") shown on the flange, yields 3.04 sq in, which, while not being much smaller (.1 sq in) than the 3.14 sq in of the OP's outlet, still doesn't classify as a 'restriction'. Of course, if we add in the cooling water flow, then maybe we should consider the 'restriction hypothesis' further...

Except for he fact that this is the elbow for both the 3JH3E, 3JH4E, 3JH5E, 4JH4E, 4JH4AE and 4JH5E, that is, a 3 cylinder, 100 cu in and a 4 cylinder, 134 cu in engine...

And, since backpressure is directly proportional to gases produced by the swept volume of any particular engine (among many other things), and the 3 cylinder engine cannot produce more gases than the 4 cylinder, it appears Yanmar, true to their business ethic (profit, as it should be), has efficiently consolidated their parts overhead by adopting a 'one-size-fits-all' perspective for this part.

Which has nothing to do with the suitability of said part for every application, or of Yanmar's concern with the economic or spatial requirements of an individual customer's application...




Fluid flow in pipes is affected by many different factors:

• The viscosity, density, and velocity of the fluid.
• The length, inner diameter, and in the case of turbulent flow, the internal roughness of the pipe.
• The position of the supply and discharge containers relative to the pump position.
• The addition of rises & falls within the pipe layout.
• The number & types of bends in the pipe layout.
• The number & types of valves, & other fittings, in the pipe layout.
• Entrance & exit conditions of the pipe work.

Of course, some 'horses' will never drink unless they're reassured by the statements of an authority figure. So be it.

But for those willing to learn, (and use the same physical constraints the 'authority figure' used, if they're any good, to arrive at their conclusion), the benefits are consistently win/win...

The recommendation to test the system with a manometer, made by several here, regardless of the pipe size eventually used, is a very good one. All other things equal, I 'd rather have a 2" thru-hull than a 3" every time...

[Snore]

Originally Posted by puffcard

I would say no.
2" the area is 3.14 sqin
3" the area is 7.07 sqin

2" only has 44% of the area, that's a huge restriction. I would ask the manufacturer.

Shhhh

I said the same thing at post #11. But let's not let physics and Yanmar ruin a fun to read debate.

[Terra Nova]

Originally Posted by jimbunyard

...The relevant dimension, the 50mm ID (1.9685") shown on the flange, yields 3.04 sq in...

You seem to know a lot that simply isn't true.

The hole in the flange has absolutely nothing to do with the desired inside diameter of the hose run. For those actually willing to understand this, consider the tiny hole provided in an outdoor water spigot. What happens to the water flow when you connect a 1/2" garden hose or change to a 3/4" hose?

Case closed.

[puffcard]

If you think Yamar makes a well engineered product and you trust their engineers. Whose only job is to engineer long lasting small engines. Why would you trust a $15K engine to a internet forum and not talk with them? I worked in submarine engineering for over 33 years, they are nothing more than a pipe filled with pipes. The calculations that go into fluid flow are complex and done with software. Exhaust pipe diameters are sized to be best suited to a particular RPM range, by the manufacture.

[Herreshoff]

Can we get a photo of the Herreshoff neriea. I'm on one also, but a cutter sloop version instead of a ketch.

[jimbunyard]

Originally Posted by Terra Nova

You seem to know a lot that simply isn't true.

The hole in the flange has absolutely nothing to do with the desired inside diameter of the hose run. For those actually willing to understand this, consider the tiny hole provided in an outdoor water spigot. What happens to the water flow when you connect a 1/2" garden hose or change to a 3/4" hose?

Case closed.

Originally Posted by puffcard

If you think Yamar makes a well engineered product and you trust their engineers. Whose only job is to engineer long lasting small engines. Why would you trust a $15K engine to a internet forum and not talk with them? I worked in submarine engineering for over 33 years, they are nothing more than a pipe filled with pipes. The calculations that go into fluid flow are complex and done with software. Exhaust pipe diameters are sized to be best suited to a particular RPM range, by the manufacture.

Could either of you, please, if you have something to say, make a coherent argument supporting your opinion???? Or provide some empirical evidence refuting mine (and several others similar, reasoned opinion, [though to label it 'opinion' is inaccurate, since the facts of the matter are hard, incontrovertible fact; the dimensions of the elbow are published, by Yanmar; the ratio of flow to swept volume is fixed (if all other variables are equal) and can be verified by actual, as well as theoretical, experimentation; the displacement of the respective engines is fixed, and also published by Yanmar])?

[kenbo]

I know this thread is old but for the sake of providing real world data...I have a 4JH3E that uses the same mixing elbow as the OP. I have a 2" wet exhaust. 3" reduced to 2" right after the elbow with a fiberglass reducer.

My wet exhaust rune is about 5 meters. I measured the back pressure to be in excess of the 120" H2O (4.35 psi)g recommended by Yanmar. I reached 120" at 3100 rpm on a 3800 rpm max. I did not go any further with the rpm test, it failed.

I'm in the process of increasing to 2.5" wet exhaust and "wasting" some cooling water to reduce volume. I'm not going to 3" because of severe limiting space restrictions.

The exhaust manifold exit hole is 45mm not 50mm as mentioned previously. I measured it with a vernier caliper. I believe the OP's engine will be very close, if not exceeding the 1200mm/47" H2O/ 1.7 psig max pressure recommended by Yanmar

[jimbunyard]

Originally Posted by kenbo

I know this thread is old but for the sake of providing real world data...I have a 4JH3E that uses the same mixing elbow as the OP. I have a 2" wet exhaust. 3" reduced to 2" right after the elbow with a fiberglass reducer...

.. I believe the OP's engine will be very close, if not exceeding the 1200mm/47" H2O/ 1.7 psig max pressure recommended by Yanmar

Why would you believe that? Your engine, being a 4JH (4cyl), puts out (across their respective rpm ranges) 25% more exhaust gases than the OP's 3JH (3 cyl).

If all other things are equal, based on your data and in your application, the 3JH would likely work just fine with a 2" exhaust system.

Of course, as has been stressed, real world data trumps the theoretical models, so the final say is the pressure test....

[kenbo]

Originally Posted by jimbunyard

Why would you believe that? Your engine, being a 4JH (4cyl), puts out (across their respective rpm ranges) 25% more exhaust gases than the OP's 3JH (3 cyl).

If all other things are equal, based on your data and in your application, the 3JH would likely work just fine with a 2" exhaust system.

Of course, as has been stressed, real world data trumps the theoretical models, so the final say is the pressure test....

Jim,

I made my estimate based on my real world data. My 1.99 liter 4 cyl reached 120" H2O at 3100 rpm using a 2" wet exhaust. So I deduced that the OP's 1.36 liter (68% not 75%) would yield similar results with the same 2"wet exhaust, .68 x 120"=81.6" H2O which clearly exceeds the allowable 47" H2O max by a considerable margin.

There are other factors to consider other than size of the wet exhaust, type of hose used, how it's run and supported, design and placement of the water lift, and total rise to include the gooseneck. None of these are known to us. That's why I said "I believe the OP's engine will be very close, if not exceeding" the max back pressure. I know what I would do but it's not my boat. Just offering an opinion based on a similar set of circumstances.

[jimbunyard]

Originally Posted by kenbo

I know this thread is old but for the sake of providing real world data...I have a 4JH3E that uses the same mixing elbow as the OP. I have a 2" wet exhaust. 3" reduced to 2" right after the elbow with a fiberglass reducer.

My wet exhaust rune is about 5 meters. I measured the back pressure to be in excess of the 120" H2O (4.35 psi)g recommended by Yanmar. I reached 120" at 3100 rpm on a 3800 rpm max. I did not go any further with the rpm test, it failed.

I'm in the process of increasing to 2.5" wet exhaust and "wasting" some cooling water to reduce volume. I'm not going to 3" because of severe limiting space restrictions.

The exhaust manifold exit hole is 45mm not 50mm as mentioned previously. I measured it with a vernier caliper. I believe the OP's engine will be very close, if not exceeding the 1200mm/47" H2O/ 1.7 psig max pressure recommended by Yanmar

Originally Posted by kenbo

Jim,

I made my estimate based on my real world data. My 1.99 liter 4 cyl reached 120" H2O at 3100 rpm using a 2" wet exhaust. So I deduced that the OP's 1.36 liter (68% not 75%) would yield similar results with the same 2"wet exhaust, .68 x 120"=81.6" H2O which clearly exceeds the allowable 47" H2O max by a considerable margin.

There are other factors to consider other than size of the wet exhaust, type of hose used, how it's run and supported, design and placement of the water lift, and total rise to include the gooseneck. None of these are known to us. That's why I said "I believe the OP's engine will be very close, if not exceeding" the max back pressure. I know what I would do but it's not my boat. Just offering an opinion based on a similar set of circumstances.

Well, it's good that you followed the more rational advice here, or your own advice, whatever, and ran a test to see what the backpressure was...

I'm confused though; which is the recommended pressure? Is it 4.35 psi or 1.7?

As you, and others previously, have said, the configuration of the system can make more difference than the size of the piping.

My deduction, based on the faulty assumption that your and the OPs' engine had the same cylinder diameters, was that 3 cylinders would put out 75% that 4 cylinders of the same size, and that the gas output volume of a 4 cylinder engine at 3100 rpm, would be roughly equal to the output of a 3 cylinder engine (with the same per-cylinder dimensions) at 3800. Of course, this was just meant as an estimate, since we both know that there are many more variables in play. A major one is that your system is 5 meters, the OP's, 3. So does that reduce his backpressure by 40%? (haha)

It is very possible that you'll find the volume of water has more to do with this than you think, or is normally imagined. The addition of a cooling water bypass line could easily have more effect than increasing the exhaust size; as you say, there are too many variables to predict the outcome without experiment.

A bonus to adding a bypass line is that, if you place the outlet where it's easily seen, one can see if they forgot to turn on the raw water valve, as well as assess the condition of the raw water pump (among other things).

If you go bigger rather than smaller on the bupass, and add a valve in the appropriate spot, you can regulate the water flow through either the exhaust or the bypass, as needed or as conditions require...