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the exhaust is pretty much 90% dry water does not get injected back into the exhaust tell just above the muffler. and the picture is a bit decieving the exhaust does slope away from the motor but not a lot. the loop in the exhaust is a good 3' above the waterline. see diagram.

I know we have spoken many times about things so please understand that I am not picking on your design. I have just never seen one like that before. That was why I reccomended discussing it with some experts (which I am not). I have simply had my fill of exhaust issues and the massive havoc they can create - which includes complete failure of an engine(s).

My first concern is what the sulphor and nitrogen diox will do to the galvanized pipe. I really do not know if they would corrode it. Also, the 1.5 seems small for an exhaust size too. The new Yanmars (for example, in the 20ish hp range) reccomend a minimum 2 inch as I recall... with more being better. If you have a long run, tight loops, high risers, etc... that exhaust hose size must be increased to allow for the pressure to get out.

The way you check this is by checking your backpressure. This is generally done on new installs at the factory. They will have the mfg reps/lead mechanic review and approve the install of the engine. This includes the exhaust (which is actually a major part of the install). They do a sea trial and make sure the thing is operating within specs. One of these tests is a backpressure test. It is the only way to be sure you have a proper exhaust.

If you have high backpressure, the cylinders will begin to run hot over time (on water cooled, especically those closest to the rear exhaust which I do not understand why). That heat then causes scoring. The scoring causes very small scratches in the wall. THat then causes compression loss. The compression loss causes engine failure.

I think your engine is a Universal? I do not know the specs for that engine, but I would guess the BP at the elbow should not exceeed about 2psi at WOT. I would need to doublecheck those numbers, but I think that is about right (on a Yanmar). If you exceed about 3 psi, you will eventually have problems unless you never run her long enough to get hot (which causes other problems).

Just some thoughts from the headaches I have dealt with. It is not meant to criticize your install, just to make sure you are aware of these things. I certainly hope you do not take any offense to my comments. I am certainly no "know-it-all". There are many people on this forum that are much more knowledgeable about these things than I am (and maybe you are too). Engines are not my strongest subject.

Brian
 

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Discussion Starter · #23 ·
No I am not offend by your comments and that I why I am posting so I can get all your opnions. I see your point on the exhaust size, one then that comes to mind right to me is why would I need say a 2" exhaust when the port coming out of the motor is only 1.5" I am going to get my hardware store exhaust bent at a shop from 1 piece of pipe. We are in fresh water, and the exhaust is dry so I am not to worried about it rusting to pieces.
 

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No I am not offend by your comments and that I why I am posting so I can get all your opnions. I see your point on the exhaust size, one then that comes to mind right to me is why would I need say a 2" exhaust when the port coming out of the motor is only 1.5" I am going to get my hardware store exhaust bent at a shop from 1 piece of pipe. We are in fresh water, and the exhaust is dry so I am not to worried about it rusting to pieces.
The only way to find out for sure is the BP test, as I said. Remember, the reccomended size is based upon a standard install. Is yours standard??? Eveytime you put a loop, a bend, a long run, a rise, etc, you increase the pressure. THink of a water hose.

Catalina runs like a 3 inch off of their 40hp Yanmar (for comparrison) and as I said, I think the minimum recc exhaust size for the 20ish hp yanmars is 2 inches with larger being better. We have actually had Catalina owners rip out their exhaust and put in even larger ones to incresae the power and decrease the fuel consumption.

The fresh water thing is not what I am talking about (though that is a concern too). Diesels put out SO, NO, and NO2 as part of their combustion, amongst other things. How will galvanization hold up to that? I wonder if there is a reason that boat manufacturers do not do it like you did? If it is corrosive to the galvanized steel (which it may not be, I really do not know), then it will have to be removed. An exhaust leak could be deadly. Isn't that the number one cause of death amongst boaters?? I thought I read that in Boat US not long ago.

That was why I reccomended calling the guys whose link I posted. Talk to them about what you did. THey could probably help provide the insulatio ntoo. Also, let us know here what they say. It will be a learning experience for me as much as you.

Brian
 

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Just on general principles I like the second diagram better than the first, as long as the indeed-critical issues of back pressure and corrosion are dealt with.



My personal situation on my boat is simplified greatly in one respect by having the exhaust on the starboard side of the hull, NOT at the transom. However, motorsailing on starboard with the exhaust submerged means I have to figure my angles well and I am thinking I want to put in a ball valve at the hull to shut while sailing.

Has anyone priced a three-inch ball valve in bronze? I have...eeep!!
 

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The only problem I have with the second diagram is why is the injection loop lower than the second loop.

That seems to be the fundamental flaw with this style system.

This is the set up I have except the second loop is 25cm lower than the first and the first is about 3ft above the water line.
 

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I expect that the exhaust pipe will break the flange where it bolts to the manifold very quickly. That is the highest stress point, and if diesels do anything, it is vibrate. I used to do exhaust pipes for our trucks, and equipment, and frequently had problems with the manifold flange breaking even when using light guage bent pipe. Even light guage pipe in that diameter will be extremely stiff. I think you would find it difficult to find any professionally done exhaust installations without a flex connection close to the engine. The closer it is to the engine, the less it needs to flex also.

Nice engine, hate to see it damaged.

Gary H. Lucas
 
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