Tuesday, January 5, 2016

Fabricating a wet exhaust system

This is an older write up that was never published.

Being the frugal (cheap) guy that I am and that I like to build things I decided I would say some money and build my own wet exhaust. (Just so you know if I feel I can't make something that is equal to or better as far as being safe...I'll spend the money and buy the part.) What is a wet exhaust you say? Well it is simple, like a car the boat has an engine that has exhaust. To get the exhaust out of the engine room you run some exhaust pipe to the back of the boat like you do a car. But the exhaust is really hot. So hot it could set the boat on fire. Yea not a good thing. So you "inject " water into the exhaust and it cools it down so you don't get a flaming sailboat...the best kind...not on fire! There is more to it than that but that is the basic idea.
Yanmar wants $350- $500 for the pieces for the wet exhaust elbow. The wet elbow is the expensive part of the wet exhaust system. I'll make that part. The rest of the system will be off the shelf from Home Depot using 2" galvanized pipe. So here goes.

This is from the Yanmar catalog.  Assembly #4 is what I will be making. The the other items will be bought from Home Depot. FYI item #7 will be a regular elbow then a "T" below that to "inject" the water....you'll see.

This is the exhaust port on the engine. It is the back of the heat exchanger.

I need to make a template of the exhaust port so I take heavy paper, tape it on and lightly tap with a hammer, end of a chisel, etc to "cut" the paper on the edges of the exhaust port.

Here is the finished template.
I purchased a 1/4" plate 3" wide and 36" long as scrap from a metal supply house. I choose 3" wide so I only had to make a single cut as the total side for this part is 3"x3". I am make two so that is why I have two in the picture. I laid the template I made over these two pieces and marked the opening I need to cut/drill. You can see I already rounded the corners of the plate.
Here I am drilling the holes for the bolts. 
Now the test fit for the bolt holes.

 I don't have a picture of it but to cut the large middle hole I drilled a series of smaller holes near the edge of it and then cut it with a jig saw.
Here is a 2" x4" galvanized nipple that I cut in two. I know some of you will say not to use galvanized piping on the exhaust due to the galvanizing out gassing when heated and making me sick. Well the galvanizing has to be really  hot like welding hot to give off gases that make you sick. I have actually seen this happen to some welders I worked with. I'm in the sheet metal trade so we deal with welding galvanized stuff all the time. Some don't take the proper precautions...the first time...LOL. They do after that!  FYI, drink milk and it will make make the illness go away.
Here is a test fit of the nipple mocked up on the plate to check for clearance.
 And wa-la the nipple is welded on the plate. I did grind the galvanizing off the nipple. It makes for a better weld and I keep from getting sick!

Here is the back side. I didn't get as pretty as a weld on this side but it will work. The 2" nipple is actually bigger than the exhaust opening but I went ahead and smoothed the weld over for better air flow.  I had actually spaced the nipple about 1/2 way into the plate and welded it there. This gave me a good place to weld on this backside without building up too much to grind off.

 Since I was fabricating stuff I went ahead and bought a sheet of exhaust gasket material. I made several gaskets as the cost for one was about $14. Now I can make many for only $8! 
Here is a picture of the material I used.
As I said before I am making two sets of wet elbows so I can carry a spare when we are out sailing the world. These things do rust out so I'll be prepared when it falls apart from rust!

So I wrote about the west exhaust awhile ago. The wet exhaust has worked great. I  wrapped the whole thing with header wrap I bought from NAPA. The header wrap will help me keep my skin. It insulated the hot metal exhaust from my arms because sure as water is wet I would burn myself if I didn't insulate it. I have found now that I have had it installed for awhile that the header wrap is really itchy. I found I have to lay across the engine from time to time working on the engine of the forward part of the engine room. So I think I will sew a cloth cover out of scrap sunbrella that I have to go over the header wrap. That should stop all the itchiness and should not catch fire as the insulation gets warm but not hot.

When I get back in the engine room I will take a few pictures to show the final installation.