bertram31.com

I just purchased a set of primax silencer at a great price. They have a anti back flow system(flapper) built in. My question Is should I still install surge tubes. Thanks Joe

Joe,
I am not familiar with your mufflers i purchased a pair of the Centex mufflers as I decided to go with 6" exhaust. (i had to raise the deck about 1.5 inches to make them work). This also made it difficult to fit surge tubes on the inside. I also moved the exhaust outlet to the side of the boat to stay away from direct surge. My understanding is that with a muffler installed the critical measurement is height from the exhaust elbow to muffler inlet. Most designs i have seen are about 12 inches to be safe. If you have less than 12 you may want to consider surge tubes. There is probably a formula one of the more experienced readers may know that would allow to reduce the size of the tube capacity necessary for straight exhaust as compared to your system.
Good luck,
Rick Kral

Anything mechanical can fail. Flappers can stick open. Why gamble with an expensive piece of gear for the cost of another 4 feet of fiberglass tubing?

Installing the Exhaust System (Hancock B31)

Cpt. Pat,
What type of system did you use to mount the mufflers? Was there space between the hull and the muffler or did you add an antivibation material between the muffler and the hull. With the six inch exhaust there is no room between the hull and deck.
Thanks,
Rick Kral

Rick,

The engines are the 4 banger Yanmars so exhaust system is 4", so didn't need to raise the deck, (muffler diameter is 9.06"). The mufflers ride in sealed mahogany cradles and each cradle has a strip of 1/4" neoprene rubber under the exhaust hose, with the exhaust strapped down in the cradles.

You could save space between the deck and exhaust by using the Vernatone Mini Max which has a 10.04" diameter for 6" exhaust system as opposed to the 12.20" diameter full sized muffler. The Mini Max also has a shorter length... I believe JP is using the Mini Max on his 6BTAs. There's not a great deal of loudness between the two different styles.

Rick, I went with 6" centubulars made by centex, they do have a cone inside to reduce back flow but I also went with Y surge tubes, made my own since nothing off the shelf will fit "just right", gives you piece of mind, make sure you pitch exhaust back as much as possible, also keep 12" above water line minimum from shower head, that last cyclinder loves to suck in saltwater. BH

Bob,

What HP are your engines? The Centabulars are only rated to 280 HP for diesel...

CHIMERA uses 6" Centek Centubular mufflers.

When the installation was tested there were no issues according to Cummins

Cummins still calls for 5-6" exhaust on their installations of 270-330 hp engines

The 5" Centubes have been used on the 270hp installs with the same passing results. I believe Centeks numbers error on the side of caution

I know of at least one installation of QSB's using the primed with the mechanical flapper and it also has surge tubes as a precaution

The centubular mufflers are noisier at idle than the vernatone models

Capt. Getting old?????? You were thinking of Phoenix remember the the controversy when I first announce what I did? The first thing you did at the Montauk gig was to jump on my boat and check out the mini max exhaust . Cockpit is stock height with exhaust up and over on cummins 330 hp and piped to outside. You can back up 15 knots all day ,I shut my engines down offshore if the boat is at idle more then one minuite. I run on one motor all the time when trolling and back up with one motor running I done everything possible to slug a motor. The up and over in combination with one way mini max mufflers and full cone shield but MOST important the sprinkler head is in the exact verticle position.so you don't get a hot spot and inturn short life on the sprinkler head . The exhaust sprinkler head is perfectly surrounded by the cooling water .there is somethink else which Carl is going to add to his list of Phoenix "tricks" and that is the harmonics set up by bringing the one muffler within 48" of exhaust turbo outlet.causes a savaging effect above 2400 rpm. Surge tubes would be as useless as tits on a bull and interfere with generator location.carl look very carefully and enlarge photo of Phoenix on images posted on site observe the exhaust/water flow from 6" exhaust .i have no idea why every diesel/ 31'bertram does not make this a standard .

Hello Bob -
Last we spoke, i believe you were installing 370 hp motors. Cpt. Pat mentioned the HP ratings on the mufflers. After a bit of Q&A with Scott at Centek it would appear that the 6 inch tubes are undersized for the HP rating. I too have a pair of 370's and after considering the function of the new recomended 8 inch Marlin muffler by Centek believe i am going to eliminate the muffler entirely from the system. The 8 inch Marlin will fit under the deck but creates a bit of piping issue from the 6 inch exhaust manifold and then again at the six inch exhaust ports at the hull. The engine exhaust is not so bad but i don't think i want to have 8 inch exhaust tubes sticking out the side of the boat (not to mention the time and expense to change my new six inch tubes). I am going to continue to do some research.

Rick

Rick I wil dol everything I possibly can do to help.i have both took part in and experimented many hours on the subject.years ago we spend hundreds of hours doing " burn outs" preparing for the NHRA nationals in Indy.1835 hp from a 500 " big block with a single four barrel was unheard of at the time .S&k/Zulu won the nationals and beat the best of the best on the final run ,pro stock national champ,in addition to B stock world champion offshore boats exhaust system was one of the most radical at the time and contributed tremendously.i used every little " trick" I possibly could on my 31 Bertram exhaust and knew all along it had to be quiet or the wife would go bezerk reminding me of the young grandchildren in the boat so I had tough odds but it came out flawless with about 3 or four hp gain from harmonics as a plus.you need a whole lot of things going for you to exceed 2 mpg this is one of them.

rick this is the exhaust on port side. notice by going up and over from turbo the height of exhaust is even with gunwale or coaming boards, port is the same height as the exhaust goes across it comes to 4' by 6' adapter to 6' sprinkler head where the raw water from heat exchanger comes in in a perfect circle within ss sprinkler head .cool to touch 360 degrees. port has same set up next exhaust and water go thru blue silicon hose and into 6" mini max exhaust were a inverted (one way) cone helps the flow by putting exhaust to inside and water to outside of 6" rubber exhaust hose . i use coast guard exhaust hose to further quiet exhaust all the way to bronze outlet. back up wot. if you could!!!! water surge cannot get past cone then 90 degrees uphill then thru sprinkler head not happening!!!!.

muffler has large one way arrow

Rick, My engines are 370s the inside of the centubular is wide open with just a slight wedge molded inside with nemerous holes. If 6" pipe is adequate I believe the centubular should work just fine, if I find it adds backpressure I will remove the wedge and go straight pipe. These engines are not loud exhaust wise, the turbo blows the sound away pretty good. I tried to "fit" the mufflers that corresponed to the HP, give up all the fishboxes and lot more $$$$, get on a 31 with straight pipes...Not annoying at all, nice commercial rumble. I will let you know soon enough, Im getting her wet THIS year..BH

no mufflers for me

Bob L. - Thanks for the photos and info. All will be helpful as I begin preliminary installation of the motors.

Bob H. - The six inch semed to make sense to me as well but the conversation with the folks at Centek confirmed that the 8 inch is required for the HP rating. After analyzing the make up of the tubes it seemed like it was a lot of money to spend for what amounts to rigid exhaust pipe. It will be interesting to compare the difference.

Rick

I would respectfully disregard the muffler manufacturer rating and go with the engine manufacturers recommendations. I know of plenty 8.3 liter engines that put out the same horsepower as our 5.9 liter engines with considerably more torque. I would guess as an exhaust manufacturer you would rate at the worst case scenario for your product.

jp, personaly I would agree but i spent a lot of money on new motors and don't want any reason for the warranty to be voided. As you may be aware, manufacturers look for any reason not to cover a claim. I am sure Centek is covering their ass but if anything did happen i would have no claim against them either. I also do not believe the Centubular mufflers offer much in the 31 system to warrant the $1,300.00 each price tag.
Rick

the fact that they fit, allowed the creation of in deck fish boxes without raising deck height when exhausts were moved outboard and passed all Cummins back pressure tests for warranty certification I'd guess they just work perfect in the b31 application. The length of the units reduces the cost of exhaust hose can be glassed right through the transom and with properly installed surge tubes doesn't require mechanical check valves in line. You can use standard Cummins risers with confidence as it is sufficient vs the more costly port side cross over.

We anchor and drift in some real crap without ever worrying about starting the next morning. And yes this boats been backwards at the upper end of its rpm range on several occasions, I can't drown it.

The more simple you make it the better.

And remember their is only one GOD of engine warranty and its the engine manufacturer. Follow all of their recommendations. Good Luck

Bob L,
how difficult is it for you to change out the raw water pump with the genny sitting there?

Eric

The generator is on a SS. Track. By removing rancor 500 gen filter which is mounted on a dovetail plate for easy removal,I then slide back the generator. The fuel filter is already move to inside nothing serviceable between engine and gen.

track, huh?
all of you guys never stop amazing me. just another idea to add to the rebuild.
thanks Bob.

No rocket science they sell SS track to be used to mount a double seat on a base with the ability to move in and out like a car.
I know this is not related brothers but it is very important and should be noted.ok I have a single fuel tank that hold 231 gallons of fuel so iam cool I can go to any canyon stay overnight and troll all day without any through of fuel------ right. No wrong! Yes in theory I can go 450 miles But the fickle finger of faith can occur anytime WATER in fuel. On the photo with generator, engine shown there is a 500 rancor just for generator mounted at bottom there is a wif.( water in fuel) alarm on bottom of fuel bowl this is connected to a buzzer hopefully I never have to hear it.obveous I do not need a ridiculous large filter for 4kw gen but this is smallest raccor that (wif) alarm fits in from factory.