Warring Bad Exhaust Design

[Paul F]

As many of you know I have had my 1980 Hunter 33 for about 10 years now, running the 2QM15 Yanmar as an auxiliary. This last July I ran aground on sandy Three Rooker Island when Hurricane Bonnie took the water out of the intercoastal. I ran the engine trying to get off in very wind blown water. The boat was tipping back and forth. Finally gave up and called for a tow. After getting off, the engine immediately began to run extremely rough. As it was night I anchored and waited for the next day. In the morning while the engine started it was rough running and would not rev up at all. I was about 10 miles from home, so sailed there. Restarted the engine to get in the pass and into my slip. It started but rough running and no power. Made it in and shut it down. I spun and started the engine the next day before leaving for two months. When I returned the engine was frozen. When I took off the head the cylinders had sand in them. It appears the engine needs a complete rebuild to run again. Rather than do that I am buying a new engine.

When an experienced engine installer looked at the boat he said the exhaust set up was designed to fail, as there was no loop in the exhaust. To review, the exhaust ran immediately down from the manifold in an elbow to the muffler under the fuel tank, then directly out the thru hull a few inches from the waterline. He said that any healing of the boat brings water/sand directly into the engine. And that is certainly what happened during the windy grounding.

If your hunter has the same exhaust design as the 33, please consider redoing the exhaust as soon as you can to prevent the intrusion of water and sand into an old engine on a bad day.

 

[Blaise]

It is difficult to believe that water and sand could be forced into an engine that is running. What I think is more likely is that you blew a head gasket and water and sand entered that way. I have never seen a vented loop on an exhaust system, but I am sure they must be out there somewhere. I removed the original 2QM20 in Midnight Sun and installed a 3GM30. Neither exhaust system had a vented loop. 6000 hours on the first engine and 4800 on the present. I used a plastic Vetus waterlock muffler on both.

 

[Ed Schenck]

It's not a vented loop, just a loop. My 2QM20 and my new 3YM30 was and is installed that way(pic). The better option might be Blaise' waterlift muffler. But I have never had a problem. And since I installed a new custom muffler recently I do not intend to change.

Don't know what to think about sand in the cylinders. Strange.

 

[kloudie1]

Exhaust Design

I wouldn't think there'd be a problem with sand intrusion while running, either.. I have a vented loop between the engine and the exhaust elbow..(mounted above the engine on the back wall of the engine box) and I have a loop in the pipe before it goes to the thru-hull exit.. (background of picture with battery box)..

 

[Paul F]

I hear you guys and before this happened I agreed with you, but I first learned of this from a powerboat mechanic. He said that many older engines let sand in when boats are grounded. Normally it doesn’t affect sailboats because of the keel, which keeps the boat higher in the water away from the sand. On the night this happened the sea was full of sand as the boat pounded on the low sand island. Here is an article I found which I think says how it can happen.

http://www.marinemechanic.com/site/page66.html

it says:

Problems occur because on almost all sailboats, and on many powerboats, the engine is installed below the waterline. Even if it's not below the waterline when the boat is at rest, the engine may well end up there when the boat heels, or when it is heavily loaded. This latter case can be particularly dangerous: because the boat's designer or engine installer may not have adequately planned for it. If the engine is or any time below the waterline, any cooling circuit that allows raw water into the exhaust has the potential to set up a siphon action. Water may siphon in from the water injection side; or, if the exhaust outlet is below the waterline, from the exhaust outlet side.

And

Whatever the mechanism, once the exhaust fills with water, the water will back up the exhaust pipe into the exhaust manifold and the engine. If the engine has more than one cylinder, one or more of the exhaust valves is likely to be open. The water will run through this valve into the cylinder below, and will then dribble down the sides of the pistons and rings into the crankcase.

This is likely what happened to the engine on my boat.

 

[Paul F]

After looking at an electric engine and other diesels the boat is now powered by a Yanmar 3YM20. I am in the process of putting the boat back together now. Here are some photos of the installation. First a vented loop for the water line from the engine to the exhaust elbow. This loop runs way up inside the back of the cockpit seats. The other vented loop in the picture is for the head. The next two pictures are of the water lift muffler and the exhaust hose looped high in the lazarette from the muffler to the thru hull. This installation is very close the the recommended Yanmar installation for sailboats.
http://www.yanmarhelp.com/i_exhaust.htm

 

[Ed Schenck]

So you bit the bullet Paul? A really big bullet. Same engine as mine except 20 instead of 30. But I don't have that same exhaust elbow. Mine is just like the old 2QM20, angles down from the heat exchanger. Was that a standard part with the engine? Maybe a few more pictures from the front showing the overall installation? Makes for a Merry Christmas.

 

[Paul F]

O.K. Ed, was down to the boat today doing more to put it back together again. Here are some pictures of the exhaust elbow. It is the one that came with the engine. I don't know why there are two types. In the picture you can see the water hose from the heat exchanger which goes to the vented loop and returns to the exhaust elbow.

Then three pictures of the engine. It fits well although tight on the sides. All of the access is on the starboard side for oil filter, drain plug (yes there is a drain plug now). This is the opposite of the old engine. I have made a much larger access opening through the head to the engine, so this change of engine access should work out alright.

 

[sandpiper10471]

LAst summer I hydro locked my fairly new Nanni 30hp. Twice!!!!! Filled the two back cylinders and filled the air intake chock full with water. Poor installation to begin with. Had there been sand in the water it would definitely have destroyed the engine. After 2 1/2 seasons without a problem, all of a sudden I had a serious problem. Engine just getting broken in after a couple of hundred hours? Bad combination of circumstances? Rectified the situation: raised the h2o intake strainer above the waterline, installed vented loop between water pump and exhaust elbow, installed waterlock muffler, removed kink in transmission cooling line. Hopefully no more hydro locking. Time will tell.