bad design of exhaust system?
 

The 1969 Irwin 28 CIB I have has an A4 with a water-lift muffler. The problem I'm having is two fold. Water flowing back into the exhaust manifold and thereby into the engine and hard starting. The more I've looked at the design of this system the more I think there ought to be a dry loop ahead of the point where the water from the exhaust manifold jacket gets sprayed into the exhaust hose.A) Has any one else had this problem? B)Would the addition of 3- 90 degree elbows a 3 inch long nipple to gain height above the manifold, a close nipple to join the pair to form the loop, and a 4 inch nipple to lower the attachment point for the water injection point so it's below the manifold oriface by at least half an inch, solve the back flow problem?

I don't think it will solve, but it should help. I have the same problem in my Catalina 30..the 'dry stack' puts the manifold exit just barely up from horizontal where the water is injected. Although the metal is sound, I took it off since I'll be replacing all of the soft hose in the system, and had some between the injection point and muffler. I am considering re-designing this as well, but knowing about the possibility of water backing into the system will likely remind me to close the thru-hull if it doesn't start up easily.

http://www.abycinc.org/committees/P-01.pdf
http://www.boatus.com/goodoldboat/Marine_exhaust.asp
http://www.yachtsurvey.com/exhaust_risers.htm
http://www.yanmarhelp.com/i_exhaust.htm
and a search for exhaust posts here in Don's forum might be of interest too.

my version of exhaust(cool runnings)
 

I saw this thread was active so I just thought I would share a schematic drawing of the exhaust on my 68 Columbia 36.
Not all the features on this boat were first class, but the exhaust seems to be well thought out and nicely made. It is dry all the way to the transom with the water only injected just before it leaves the boat. The hot gases are cooled very well with a water jacket heat exchanger and then the water exits the heat exchanger by a hose and is injected into the exhaust after a high loop at the end of the pipe. This stuff is all bronze or brass and looks pretty healthy after all these years.

The high loop at the end is just single wall exhaust pipe but it always runs cool. The previous owner had fenders and ropes and stuff crammed in the lazzarette (sp?) against the heat exchanger with no problems of burning or melting. And, the single wall pipe at the end does have some fiberglass insulation around it just for extra safety.

We realized the beauty of this system when we were cranking the engine a lot to chase down an ignition problem. We thought we might fill up the engine with seawater through the exhaust so we stopped:eek:. After analyzing the system I was really happy to find out that would be very unlikely. A following sea in rough weather might be the only problem here, but a simple flapper might fix that.
This all responds well to the first rule of boating; "Keep the water out of the boat":)

Russ

Bad design
 

Since the majority of the problem seems to be at start (or non start) and difficulty of getting to the seacock to shut off (starve the pump) the raw water to keep from filling the exhaust with water and having it flow back into the manifold into the engine and then when the engine starts reach over the running engine to re-open the seacock in time to not burn up the impeller, it seems to me that rather than shutting the raw source flow off, installing a diverter valve in the line from the exhaust manifold to the injection point that could shunt the flow overboard until the engine starts running and then return the flow to "normal" allowing water into the exhaust would solve two problems. A simple cable actuator (like a choke cable and bell crank) with the pull mounted adjacent to the choke pull, for would fix one issue (access) and the diverter would solve the water backing up in the exhaust problem without creating the dry pump risk.
Does this sound reasonable to you ?

Rise in dry stack works for me
 

Pater et al.,

On my 75' Tartan 27, I have a dry stack rising up about 12 inches above the water line before the water is injected, and flows downward to the water lift muffler, and then a steady 6" rise for the 6' run out. I have an exhaust check valve just before the outlet in the transom.

I do have to snake the dry exhaust forward about 6 inches from the manifold outlet to get the vertical space for the dry stack to go up though, and it is well taped with insulation. I do have 5-second access to the cooling water intake valve on balky startups.

I have encountered no problem in 5 years, with some heavy weather, but am looking to add a few more inches in the dry stack rise just in case--because I can.

Mary

Mary,
This discussion has also led me to think about a re-design of my Catalina 30 exhaust hot/dry stack setup.

I think I can get 4 or 5 more inches out of it if I try. Currently it runs almost horizontal to the water injection point which then goes into the muffler. I think I can make a loop that goes up 6", across about 6" and then down to the same water injection point.

This forum is great! I have learned so much about the good (& bad) designs of various A-4 set ups!

Incidentally, my local Lowe's has zero 1-1/4" galvanized pipe or fittings for the hot stack....there is apparently a plumbing supply store about 20 minutes out of town I plan to visit next week. At least the Lowe's employee recognized what I was trying to do when I brought my old pipe in and had a suggestion.

bad design
 

So I take it no one thinks much of shunting the coolant water overboard with a three way valve between the exhaust manifold and the injection point in the drystack thus avoiding ending up with water backing up into the engine.