You haven't had the full C34 experience-failed exhaust riser

[SteveLyle]

until you've dealt with a failed exhaust riser.

I now get that opportunity.

We were motoring out to the lake about halfway down the Genesee river breakwater.  The fast ferry catamaran decided to depart about that time for Toronto, and was even with us.  Since she takes up half the channel herself, there wasn't much room for the rest of us, including the cigarette boat off my stern that thought 6 knots was too darn slow.

I had checked the engine gauges and everything was in the green.  Then there was a sudden change in how the engine 'felt' - just a change in sound, nothing dramatic.  RPM's dropped a bit (I still haven't figured that one out), and it felt like a bit of a loss of power.  Then some smoke/exhaust coming out the companionway.  Then Pam mentioned water on the cabin sole just fwd of the engine.

I put my son at the helm, and headed below.  Once the engine was uncovered, the problem was obvious.  The exhaust riser had failed at the flange.  The raw coolant water couldn't get pushed out the muffler, since it wasn't getting any exhaust pressure, so it backed up the riser and was flowing out the broken end back into the engine compartment.

So things were wet and smoky, but the engine was actually running fine, and would, since the coolant leak was downstream of the engine.  

Back at the helm, we waited for the ferry to pass, then headed back to the dock at about half throttle, simply because I didn't want to pump too much water back into the boat ("Keep the water out" - isn't that one of the key rules?).

I really feel bad for you guys that have to deal with salt water.  My flange bolts, which haven't been touched for almost 20 years, came right off (ok, the bottom one was frozen, but the stud came right out).  When I got the riser home and unwrapped, it looke brand new, just a bit of surface rust.  The raw water nipple was brass, braized into a short length of 1 1/4" brass pipe, and looked great, just a bit of soot inside.  In fact, my repair strategy is to somehow get the flange-end pipe length (which broke at the flange threads) off the riser, and simply replace it, keeping the rest of the riser.  A new flange and gasket, and I'm back in business.  I'll also take this 'opportunity' to switch to a hump hose and replace a few other hoses that are showing some cracks.

Just when I thought I was getting off easy, the anti-freeze drain valve on the engine block fell apart.  I haven't figured that one out either, but I figure Universal can sell me another one.

I'm still trying to figure out my sense that the engine lost some power.  Would zero back pressure reduce power?  Was it my imagination?  I'm thinking it must be - the enginee being noiser makes sense, but not losing power.

Anyway, got a lot of parts to order tomorrow.

Steve

[karista]

Steve
Where exactly did the fracture happen? How old was the heat riser?
Where do you keep your boat? I used to sail out of Oak Orchard Yacht club. Sailed her down a few years ago to the Gulf coast (St. Petersburg). Thinking about sailing her back to Lake Ontario. Between the hurricane warnings each year, the barnacles which build up and the diver cleaning service which never shows up, the hot, no wind summers (except when the tropical storms hit, quite frankly I get less sailing done here than I did in the 3-4 months of season on Lake Ontario.
In addition the constant hurricane preperations have taxed my patience. So let me know where you keep your boat on the river.
Bernd Mueller

[Ron Hill]

Steve : Sounds as though you had your hands full.  
As I wrote in the Mainsheet way back - Catalina started using stainless risers on hull #320 something (as I recall).  Before that they used black pipe.  Nothing wrong with black pipe, but it doesn't last as long as stainless.
The Kubota dealer will have a new drain valve at 1/2 the price.  Take the old one off and match it.
Failure at the flange - interesting.  

[SteveLyle]

Bernd,

We dock and store at Shumway Marina.  Nice facility, and very convenient.  I can be there in 20 minutes after work, 25 from home.

The engine has 590 hours on it.  This is my 4th season with the boat, bought in the fall of '01.  No way to know for sure, but I'm guessing that the riser is original, meaning 19 years old - I would think that if it had failed on the PO, he would likely have gotten a replacement from Catalina, and it would be stainless.  Of course, I could be wrong - maybe it failed for him this same way, and he just replaced the same section I'm going to.

It broke at the thread right at the flange.  Not too surprising, there's a lot of mass cantilevered out there, the engine is vibrating it this way and that, eventually it fatiques and breaks.

A weld/fabrication shop got the old '1st segment' off and put a new one on for $20.  I ordered all the parts & hoses today, will be out of town this weekend but should have it all back together by the middle of Sept or so - with maybe a month on the outside left on the sailing season up here.

I figure when the boat gets hauled I'll take off the repaired riser, send it to Catalina and get one of the newfangled stainless ones.  That'll give me a spare.

Our original plan was to take a season ending sail to Sodus Bay this past weekend.  But it turns out that that was my plan, not the crew's plan.  And when all my fixed ports decided to leak at the same time (that's another post for another time) it seemed the better plan was to fix those and head to Sodus some other time.  After the riser failed that was an even better plan.

[Paul Blumenfeld]

Steve,

I talked with Catalina parts today and they said if I brought them a black iron riser they would make it the same, not replace with stainless.  Did you get a new one out of stainless?

Paul
#312

[SteveLyle]

Paul,

No, I ended up making my own out of Home Depot iron pipe.  Figure that I'm good for another 19 years.

Interesting - I wonder why Catalina would say that - did they give you a reason?  I would have thought that if you were willing to pay for one made out of gold pipe, they would have done it.

Steve

[Stu Jackson]

In addition to Ron's many posts on this subject, refer to the February 2004 Tech Notes Online for my writeup on a failed riser and its replacement from Catalina.  Searches here on exhaust riser will pull up the earlier discussions about black iron vs stainless.  Steve, glad you made it back under power, when mine died it was at the nipple, but I got a great long sail home out of it!

[Ron Hill]

Guys : I've had two replacement risers.  Both were stainless.  One cracked at the raw water nipple entry and the other I believe was at a weld under the wrapping(I didn't take it apart, but Catalina did). 
The most frequent break point is at the nipple.  Just remember to stake weld the nipple on the inside for extra strength.   

[tstrand]

We just had the failed riser experience, too. The engine compartment got a good coating of exhaust grime but we managed to motor home without choking on the fumes. Ours broke both at the flange and the nipple. I think the nipple had been leaking because we could smell some exhaust in the head before the event.

Catalina told me the same thing they told Paul: if I send them a black-iron riser, that's what they'll send back. Ours is stainless so we got stainless back.

Catalina's first attempt at making a replacement was unsuccessful; the angles were off so far that it couldn't reach from the riser to the muffler, even with a new silicone hump hose. I sent it back with a detailed drawing on how to make it right. Their second try didn't fit either but I discovered that I could make it fit by unwrapping all of the insulation (wear gloves and a dust mask if you attempt that - fiberglass dust everywhere), untwisting the threaded elbow they use for the first turn by about 15 degrees, and then reassembling the whole thing. All reassembled now and no exhaust smells, so we're ready for a test drive.

The whole job would be very quick and easy if Catalina delivered an exact replacement. I think in our case they lost the reference angles because the nipple area was so corroded. It would be almost painless to do this job before the riser fails, if you can figure out when that is...

[Mike Vaccaro]

Another possibility is local manufacture.  We had a local company that specializes in marine machine applications built a replacement for our boat two years ago.  In accordance with some good advice posted on the site in the Mainsheet, we used heavy walled tubing and paid particular attention to the water injection nipple.  We also used fiberglass tape for insulation (held in place with stainless safety wire).  This makes the riser easy to handle and remove for maintenance.  Each time the riser is off, it should be inspected.  It's a good idea to keep a spare exhaust riser gasket on board in your spare kit.     

Have also found that some high temperature RTV in conjunction with the gasket is helpful to prevent seepage of glycol into the exhaust.  This seepage is generally the result of a less than perfect surface on the flange which will degrade over time.  If the flange is in generally good condition, it's surface can be refaced by machining or with sanding/polishing. 

Replacement flanges are available from several sources and are plain steel, so they require some occasional preventative maintenance for corrosion control even when your pipe is stainless.

Best of luck,

Mike

 

[Ron Hill]

Mike's got some good advice, as that gasket between the flange and the engine is only a couple of $$.  You might also consider an extra flange as the old one may be a bear to get off!!
 
One of the problems that the factory "induced" is they added extra layers of insulation around the new riser just aft of the flange.  This extra thickness caused pressure from the riser on the heat exchange below and the first indication was the broken hose clamp that holds the HX in it's saddle!!  That extra pressure also could work on the screw in-thread of the riser pipe into and on the flange!!
A few thoughts.