Azimut 37.9 Exhaust System

[Santinho]

Hi all,

As all we know the Volvos TAMD*s 61 series are very smokys.

This is a problem in my new marina berth with a lot of neighbors living in their boats and when I sailing in low revs with motors only engaged and want to put some guest in rear deck.

Ownering an Azimut 37 from 1992 with "out of water" exhausts I*m thinking in change them by an "in water" outlet system, adding a tube since my transon until the water (about 5 cm inside water).

With this change I think reduce significantly the smooke around my guests and other boats.

My concerns are if the system have enought "air flush" power to let smooke get off the system.

What do you think about? Advices needed please.

Best regards
Joao Santos

 

[Divemaster1]

The exhaust gases are lighter than water, so my guess is that it will emerge up again straight away!

The smoke is probably over-fuelling at start-up (quite common to have un-burnt fuel ... grey exhaust at start-up on older generation engines), and if you put exhaust under water, you will increase back-pressure which in turn may have a negative effect (resulting in possible slower starting ... more un-burnt fuel = more smoke .... or other negative effect). For that reason, most manufacturers are building underwater exhaust systems with outlets above water for start-up & idle and diverts the exhaust under water at higher revs and when underway to reduce noise..

Someone who knows the 61 series will hopefully come along and advise on if anything can be done to reduce smoke at start-up.... but one have to assume that engines are in-tune and healthy...

 

[Santinho]

Hi Divemaster1, many thanks for your reply.

I read about and d`like to see an underwater exhaust system with outlets above water. I`m gonna seek in the internet.

The engines are in perfect condition but the smoke is a little bit unpleasant. I know is a factory fault but I like to improve for modern standards if its not to expensive and, most important, if it works.

I saw and take a picture of an Jeanneau Prestige 36 with something like a underwater system but I dont know if is a factory setting.

Best regards
João Santos

 

[Divemaster1]

The picture below is of an Azimut 39 with underwater exhaust ... but the small outlet just in front of the fender here is the exhaust outlet which is used at start-up and idle ... once underway and at higher RPM, there is a flap in the exhaust system which diverts the exhaust under water..

I believe the trend in underwater exhaust systems was to reduce noise and to make exhaust gases emerge further behind the boat when underway (to reduce soot on transom).

I do not believe that you will have less smoke at start-up with your 61 series engines just by installing an underwater exhaust system.

 

[adey]

Hello João,
I think you are trying to solve a problem that doesn't exist.
Some other boats must smoke much more than yours.
Your engines only smoke a bit when cold and I'm sure your neighbours will be tolerant as long you don't run them for no reason in the marina.
Once underway I don't think you have a problem?
Leave the exhaust alone..

 

[david_bagshaw]

I am not certain a little back pressure causes more smoke as both Scania and Isuzu on trucks use the exhaust brake to create a partial back pressure to help combustion and reduce white smoke on cold start and early warm up.

Latestarter is the guy for the definitive view.

 

[Santinho]

Hi all. Many thanks for advices and pictures. Now, I better understand the underwater system seeing this Azimut picture. Its more complex than I was thinking.

Adey, I are you? Thats not a big problem - pherhaps I make it apear larger than he is but is not pleasant if you consider that in the firsts minutes you go sailing its unpleaseant to stay near the transom.

When I go underway at low revs they also smooke while they are cold. This could last several minutes unless you go at higher rpms for some time. After that is ok - you can reduce to idle speed with no smooke at all, but at this moment you already have burn some litres of diesel unnecessarily.

Adding to this I`m thinking to start rent the boat for short trips (2 or 3 hours) and imagine what good can be you can have customers seating in cockpit seats for the first moment without diesel smooke.

I dont know if I go make any change in exhaust system - its only an attempt to see if is possible to do with no sustancial costs.

Best regard
João Santos

 

[Santinho]

I David,

Very interesting theory. If works in trucks why not in our boats.

I gonna wait for Laterstart or VolvoPaul views.

Best regards
JS

 

[Tordjman]

Hi
I have the same boat, smoky only when the engine is cold
Have you the owner manual for the azimut 37.9??

 

[A_8]

I don't think the Prestige 36 exhaust outlet is std and probably only makes a difference at speed in that the exhausts exit further from the boat.

The type of diesel you use can affect smoke, I find that white diesel exhausts smoke and smell a bit less.

 

[Portofino]

Amarti the designer and founder of Itama was the first boat builder way back in the 80 s to use under water exhausts .
There is a back pressure issue and thus there needs to be always a way out , in effect a fart pipe to the transoms for when the boats off the plane and doing marina movements .So just attempting to divert it all @ tickover speeds is gonna upset the back pressure side of things .
At static or berth movements your smoke will just escape out of the fart pipe , you are gonna need one any how .


The Amarti method is a shelf that causes a vacuum at speed , so when tonking along virtually all the gases exit under when running .
The gas vol is not linear with rpm s as the EGT s temps go ballistic , tick over under a 100 , running my boat typically mid 500 s
Those kinda temps are gonna hugely effect the pressures .We are not talking about leaving a can of pop on the back seat of your parked car in the sun here .Heat the can to 550 degrees and pull the ring pull ?



The under water bit note the step to create suction when running .


You can see where the fart pipe comes off the underwater collection box , and has its own cooling water feed.

It’s a complex subject and engine manufacturers would have signed off the design and tested .
Indeed I just had replacement exhausts in SS fabricated and the MAN agent has done a final seatrial + sign off .

As others have said just accept it , or get the injectors serviced along with possibly the pumps ……..but if it all works my advise leave well alone rather than open a rats nest of back pressure problems which might shorten the life of something else , knock on effect adversely.