Side Exhaust vs. Out the Back

JohnD · Post by **JohnD** » Wed Apr 25, 2007 2:27 am

Thought I'd post this here for general discussion. I'm about 3 weeks out from starting my Diesel conversion, unfortunately timing of yard and motors pushed things back. Anyway, here's the topic: I've got a 1972 B35 with gas and 3" exhaust out the stern. I'm installing 3126 Cat's and will be changing the complete exhaust over to 6" per spec for my motors and I'll be using an inline muffler. My Options are: 1) Keep the current config and run out the back of the boat. May be a little quieter than out the side, but greater stationwagon effect bringing fumes into the cockpit. 2) Modify and exit the exhaust out of the side of the boat & if so, how far up from the stern? I'd expect this modification to cut down on cockpit fumes, though may make the boat "sound a little louder". I'd be interested in hearing the thoughts and opinions of others. Thanks, John D "Lady D" Bertram 35 Pasadena MD

Post by **dougl33** » Wed Apr 25, 2007 3:34 am

John, I know some of the guys have removed the velocijet exhaust openings during the re-powers. The guy who's doing my re-power has done several 33's. He said that for the 6BTA's its fine running with the stock gas exhaust set-up. That's the way I decided to go. Even though the job is complete, I'm still about 6 weeks away from hitting the water. I will let you know how it works at that point, though I think it will be too late for you to make a decision by then. I know you're going with the 420hp Cat 3126's, so maybe its a different beast all together. How many liters/cubis inches are the 3126's? I know the old 3208's are over 600 cubes. Regards, Doug L. 1986 33 Bertram FBC Queen Elizabeth Marblehead, MA [img]http://www.bertram33.com/photogallery/p ... sabeth.jpg[/img]

JohnD · Post by **JohnD** » Wed Apr 25, 2007 6:32 am

Thanks Doug, The 3126's are 7.24L or 441.81ci (per the spec sheet). Mine is a '72 B35 without the veloci-jet exhaust. The first time I saw one was on a later model B35 that happens to be in my creek and we were both waiting for the drawbridge to raise. I couldn't figure out what caused it to spew water from 1/2 way up the side, it only happened every once in a while. Though we've spoke I don't have his contact info to see if he likes it or not. If I switch to the side it would be a single outlet at the waterline. John D "Lady D" Bertram 35 Pasadena MD

Brian Davin · Post by **Brian Davin** » Fri Apr 27, 2007 1:02 pm

John, I repowered last year with Yanmar 370's and went to 6" side exhausts, removing the veloci-jets altogether. Came out very nice. They're 12" - 15" forward of the stern I think, but I'd have to measure to be sure. Had to cut old exhausts in half to remove and then replaced with 6" version, though a few inches shorter to be able to fit back in around the bulkhead wall behind the fuel tank. I've been very happy with the side exhaust, though, without comparing to another boat with the traditional stearn exhaust, it's hard to say if they're actually loader or not? Let me know if you have more questions. Brian '90 Bertram 33' FBC Never Say Never Guilford, CT (Homeport) Kinnelon, NJ (Home)

Chris Anderson · Post by **Chris Anderson** » Mon Apr 30, 2007 11:04 am

Hi John, I repowered from gas to Yanmar 6LP UTE 315 hp 3 years ago on my 33SF and also did the 6" side exhausts. We positioned them about 5" forward of the transom and about 3/4 the way above the waterline. I used Tiara's deflector which keeps the water from covering the outlets at slower (hole diging) speeds. This also helped keep the exhaust back pressure and temps from increasing during any times of continuing slower running. I do get some soot marks on the side, but not too bad. The sound levels with the mufflers is a nice low rumble that is about 2db below what the 454s were at cruise. 1.1 MPG at 22 knots is a real nice result. After 1100 hours they still feel new to me. You will be THRILLED. (I HAVE to learn to post pics) Please feel free to email me any questions I can answer for you. Chris

JohnD · Post by **JohnD** » Tue May 01, 2007 3:53 am

Thanks for the feedback, just what I was looking for. I already have fg mufflers and will probably just glas in 6 inch outlets. Chris, would you happen to have any pic's of the "Tiara deflector?" my e-mail is johndunker@yahoo.com Between their schedule and mine it looks like it will be another week before I get into the yard. John D "Lady D" Bertram 35 Pasadena MD

jav · Post by **jav** » Tue May 01, 2007 5:32 am

John, I would recommend side exhausts if you can. In addition to the the station wagon effect for fumes, the same is true for transom soot.

JohnD · Post by **JohnD** » Tue May 01, 2007 8:22 am

Something kind of funny is that I posted the same question on B31 as here and most of the responses there have been to keep them out the back. Once I get the boat opened up I'll look at how much trouble it will be to go out the side. I know I'm going to do that with the Gen exhaust anyway & will already have some holes in the transom to fill, so what's a couple of more

John D "Lady D" Bertram 35 Pasadena MD

richcatch22 · Post by **richcatch22** » Tue May 01, 2007 1:51 pm

Personally, I don't technically understand the use of side exhaust. My Aquasport had side exhaust, no real problems, but sound and engine performance definitely effected by sea state and running conditions due to the changing exhaust back pressure. The transom exhaust offers a free unobstructed exhaust flow when running. I have 45 deg elbow at the transom exhaust to direct the exhaust to the side and have no transom soot or station wagon effect. Capt Rich Catch 22 1989 33 FBC

Chris Anderson · Post by **Chris Anderson** » Wed May 02, 2007 3:48 am

John, One item I wish I had done different, concerns the gen exhaust. I ran it out the Stb transom.... I wished I had combined it out the stb main port (like Viking,etc as a tube within a tube) as I have a swim platform that gets too much exhaust.

JohnD · Post by **JohnD** » Wed May 02, 2007 10:02 am

Chris, Thanks for the pictures I like the way yours were done. Funny think I was thinking of combining my generator exhaust with the motors as well. Capt Rich you do have a point about the running noise, though hope the back pressuer wouldn't affect the diesels. I'd say that right now I'm leaning toward the side about 5-6 inches from the stern. Either way, I'm going to plumb the gen exhaust into motor outlet (ala the big boats like new Bert's and Vikings). Man I can't wait for the fun to begin. Cheers, John D "Lady D" Bertram 35 Pasadena MD

Capt. Ed · Post by **Capt. Ed** » Wed May 02, 2007 2:52 pm

My neighbor has side exhaust at the waterline on his 40' Chris Craft with Cats. You don't even hear it running and do flumes in the cockpit either.

Post by **dougl33** » Wed May 02, 2007 3:29 pm

How do you do flumes in the cockpit? Regards, Doug L. 1986 33 Bertram FBC Queen Elizabeth Marblehead, MA [img]http://www.bertram33.com/photogallery/p ... sabeth.jpg[/img]

Chris Anderson · Post by **Chris Anderson** » Sat May 05, 2007 6:53 am

Hi John, If you look at the "Events" section, Kiwi Too was at the Captiva Island "Bertram Pride" gathering (which was a wonderful time...) but in some of the pics you can see the side exhaust and how I get a little soot area that I mentioned before. More soot in the high temps and humidity of summer.

Sean B · Post by **Sean B** » Sat May 05, 2007 10:05 am

quote:Originally posted by dougl33 He said that for the 6BTA's its fine running with the stock gas exhaust set-up. Can that be right? I had thought the 6BTA's needed at least 5" exhaust. What's the 6 week holdup on the splash? Sean Burlingham "Island Time" 1987 Bertram 33 SF Melbourne, FL SBurlingham@cfl.rr.com [img]http://www.bertram33.com/photogallery/p ... d_Time.jpg[/img]