Good read on wet exhaust design

djmarchand

Captain
Joined
Jul 24, 2012
Posts
664
Likes
293
Location
Litchfield, CT / Punta Gorda, Fl
Boat Make
Atlas Pompano 23 outboard
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

Admiral
Joined
Aug 6, 2013
Posts
6,535
Likes
2,456
Location
Southwestern CT
First Name
Ben
Boat Make
1998 36' Sabre Express CAT 3116TA's, 2015 ROS Scotia 16 Etec 50
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

Commander
Joined
Mar 4, 2012
Posts
264
Likes
39
Location
Chico CA/Kenai AK
Website
www.alldrinsalmon.com
Boat Make
40' Snowball gillnetter
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

Lieutenant
Joined
Aug 10, 2013
Posts
69
Likes
8
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

Admiral
Joined
Aug 6, 2013
Posts
6,535
Likes
2,456
Location
Southwestern CT
First Name
Ben
Boat Make
1998 36' Sabre Express CAT 3116TA's, 2015 ROS Scotia 16 Etec 50
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

Admiral
Joined
Sep 1, 2011
Posts
7,586
Likes
3,315
Location
Portsmouth NH, boating out of the mighty Merrimack
Boat Make
25 Terry Jason with Cummins 370 power
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 ! :D
 

5akman

Commander
Joined
Mar 4, 2012
Posts
264
Likes
39
Location
Chico CA/Kenai AK
Website
www.alldrinsalmon.com
Boat Make
40' Snowball gillnetter
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

Admiral
Joined
Aug 6, 2013
Posts
6,535
Likes
2,456
Location
Southwestern CT
First Name
Ben
Boat Make
1998 36' Sabre Express CAT 3116TA's, 2015 ROS Scotia 16 Etec 50
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 ! :D

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

Commander
Joined
Jul 20, 2012
Posts
333
Likes
84
Location
seattle
Boat Make
Devlin 48 & Marshal Sanderling
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

Admiral
Joined
Sep 1, 2011
Posts
7,586
Likes
3,315
Location
Portsmouth NH, boating out of the mighty Merrimack
Boat Make
25 Terry Jason with Cummins 370 power
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. :D
 

greg

Captain
Joined
Sep 3, 2011
Posts
986
Likes
198
Location
Point Judith, RI
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

Admiral
Joined
Aug 6, 2013
Posts
6,535
Likes
2,456
Location
Southwestern CT
First Name
Ben
Boat Make
1998 36' Sabre Express CAT 3116TA's, 2015 ROS Scotia 16 Etec 50
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

Rear Admiral
Lite User
Joined
Aug 25, 2012
Posts
1,095
Likes
826
Location
Annapolis, Md
First Name
Eric
Boat Make
Shelter Island 38
Top Bottom