Good read on wet exhaust design

[Bill]

Main Article on Marine Exhaust Systems - Page 2

 

[Brooksie]

You are correct sir. Very good read.

 

[djmarchand]

Tony Athens, the author of that article, preaches several things over on boatdiesel: design your exhaust system so that water can't back up and ruin your turbo/engine, prop your boat to reach rated rpm at wot + 100, cruise your boat at several hundred (depends on engine) rpm below wot, feed your engine clean fuel with proper filtration. Probably half or more of his posts deal with one of these issues.

There are three cardinal rules discussed in that article on exhaust system design:

1. The spill over point at the injection elbow should be at least 12" above the water line.
2. The water injection should be down hill so an internal failure can't back flood.
3. An inherently safe exhaust system has the level of the spill over point aft of the water lift muffler below the spill over point at the injection elbow. That way repeated waves crashing on the transom can't build up a level in the water lift muffler to the point that it floods the engine.

On my Mainship Pilot 34, 1 and 2 were wrong with only 8" of clearance above the water line. I fixed it by raising the dry riser to allow 16" of clearance and pointed the injection elbow down.

David

 

[Toolate]

That is a great read with pictures too (I put down my coloring book to read it .

Seems like simple stuff but if you dont have room for the height and dont plan ahead, the problems are BIG as depicted by him. Thinking about every boat I ever owned right now....

 

[5akman]

Any pros/cons to complete underwater exits as opposed to out the side of the boat? I'm thinking of a wet exhaust system on my gillnetter and going straight out the bottom of the boat just inside the chine. If I go this route, do I need a muffler at all?

 

[delucat2]

You will need to make sure you don't exceed backpressure spec. You can't guess on this, you need to have a plan that you know will work.

TonyD

 

[Toolate]

I am trying to buy an older boat with a 318 Chrysler with wet logs, risers and elbows and you have just raised my blood pressure.... Plan is to replace the whole plant and will def be using the tips provided in your article.

 

[BillD]

I am trying to buy an older boat with a 318 Chrysler with wet logs, risers and elbows and you have just raised my blood pressure.... Plan is to replace the whole plant and will def be using the tips provided in your article.

Toolate,

If you have not already, hop on to boatdiesel forum.
You can spend weeks reading/learning of exhaust failures that have taken out more marine diesels then you can count !

 

[5akman]

Tony,
How do you measure back pressure and where in the system? Just a normal pressure/vacuum gauge? And where would I tap into the system to check? Do you sell the mixer units?

 

[Toolate]

Toolate,

If you have not already, hop on to boatdiesel forum.
You can spend weeks reading/learning of exhaust failures that have taken out more marine diesels then you can count !

Did that today. Only took about 50 suggestions for me to come around..... great place though the format really sucks for a forum. The info is there though.

 

[eyschulman]

Tony's tips

Tony's stuff on exhausts is great I used it as a model on my build and it worked out well. At the seaboard marine site( Where tony is based) and on boatdiesel.com there are many more informative articles written by Tony Athens. Its great that a guy with Tony's experience and knowledge shares what he has learned with all who will take the effort to read it.

 

[BillD]

Did that today. Only took about 50 suggestions for me to come around..... great place though the format really sucks for a forum. The info is there though.

Boatdiesel forum is ALL technical posting, technical specific sections etc.
ANY crappola, chit chat, non technical postings etc. are deleted by the admin folks within a day or two.

 

[greg]

Tony has far more patience than any techie I know. He tolerates fool after fool, many of whom are in abject denial over what the real problems really are.

Great site. It has saved me a lot of money and is beginning to give me a clue how to manage a diesel engine.

 

[Toolate]

Not sure why that site is not set up like this one though (this format for a forum is proven to be a winner). I might if I were an internet type of guy...

Tony is the man as far as I can tell. The hundred hours or so I have spent reading all these sites has brought me to that conclusion.

 

[OLD BAY]

Tony is the man as far as I can tell. The hundred hours or so I have spent reading all these sites has brought me to that conclusion.

X2 on that. That forum must have saved me thousands of $$.