Exhaust soot in various lockers

[GarthP]

repost from pbo forum

Hi all - any advice on this appreciated.

Recently completed a trip - Mallorca to Barcelona and back in our Predator 72 (recently acquired). With 2-3M seas on quarter for some of the time we had some rolling to contend with and when we arrived we noticed that the cockpit sink and ice-chest were completely full of diesel soot/smells. Later we realised that the same thing was happening in both aft rope lockers. With black rope, we had not noticed it before, but when washing down there has always been some residue on the ropes that we had put down to being stuff picked up in the marina. Now we can see the build up on the inside of the lockers.

I assume then that all these spaces have drains that exit into the same holes in the hull used by the exhaust and that back pressure during lively passages is forcing the exhaust gasses into them.

A set of bungs may be the simple answer - tried one in the ice chest so far and it seems to be OK but not tried under the same sea conditions (actually a wine bottle stopper commandeered for the trial!). Non-return valves have been suggested but I wondered how effective they would be at stopping gas returns as opposed to liquid. Even considered re-routing them to drain into the bilge...(but not for long).

Any thoughts or pre-canned solutions?

Cheers

Garth
Read more at http://www.ybw.com/forums/showthread.php?457674-Diesel-soot-in-various-lockers#OwMcFRRFjAMBWu5u.99

 

[dpb]

I have no experience on that type of boat but can't imagine a path from exhaust to locker. Are you sure it isn,'t damp and mould?

 

[omega2]

If it is not going out the back then the exhaust system has to be the culprit, check from elbow to outlet, any reinforced rubber bits could be delaminated/cracked, any fixings clips etc could be broken, Do you see any black smoke when engines are running, I know its a long way from your helm to your stern LOL

 

[Portofino]

It will be what you say. But not from the exhaust direct. It will be most likely from the under water box that the main exhaust is ment to discharge .

Some will be piped to the stern via tubes glassed into the hull or proper E tubing ,bit most will be intentered to exit via the "underwater box " -idea is less noise .Mario Amarti ,designed / kinda invented it on his Itama range - , since then the concept has been copied .

Mine have a little spoiler or deflection plate that creates a -ve pressure ,faster you go the more suction hence the gasses and any drains the direction of travel is out .We have no external holes in the hull on the sides -everything exists via the exhaust boxes or other underwater holes .

Crucial factor being the hieght of the box in the E room ,taller the better but that conflicts with engine instal riser hieght ,that need to be a nice big arch if poss ,not a low one otherwise potential water backlash .you don,t want that = knackered engine

Having said that in 1/4 or rolling sea than occasionally if a "box" is exposed to the surface we hear a big roar then a gulp as it splashes back under .
Never noticed any regurgitation .
All I can think is that the box design has not been thought out ,not high enough in the E room so when the boat roles back water is forced up back through passive holes ( engines has +ve reassure via gases ) ,
Or the combo size of box /transome pipe diameter is wrong ,leading to back pressure in certain rolley sea states .
It's prob water ,soot In feasted water so fit corks for now ,but try none return valves on the offending drains -try and go out in a sea state and get it rolling to eye ball it first .
You can,t alter the box , or the risers .
Never ,I mean never ride with one engine OFF in a rolley sea = no back pressure = water enters the exhaust riser ,which may be low ,explaining why the box hieght is low , in the 1 st place -leading to what you have .

As an aside we had a Sunseeker Portofino on drives -one of the bilge pumps in the engine compartment used to regurgitate oilly bilge fluid into the cockpit sink and cool box -nice -I used wine corks for a fix .

How fast we're you going , hmm hang on more rpm = more pressure ,but if designed right in the first place -underwater exhaust should increase suction as speed increases .

Really need to see pic of engine install the arch on the risers - hieght of box in the E room ,and the under surface of the box in the hull .

 

[Portofino]

1- As an aside we had a Sunseeker Portofino on drives -one of the bilge pumps in the engine compartment used to regurgitate oilly bilge fluid into the cockpit sink and cool box -nice -I used wine corks for a fix .

2- How fast we're you going , hmm hang on more rpm = more pressure ,but if designed right in the first place -underwater exhaust should increase suction as

my Diagnosis from an arm chair ---/

1- are you sure it was not Olly bilge water -rough sea spray - and all water sloshing bilge pumps -on /off
2- long shot -you cruised too slow and exhaust pressures in the box all cocked up

 

[rafiki_]

A couple of seasons ago our props became badly fouled. Knocked more than 10 knots off the speed, and resulted in a really smokey boat, where the exhaust, underwater on ours, pulled bcc over the boat in the turbulence. Took some cleaning! So before you start fixing the complicated things, check the hull and prop fouling.

 

[Promarine11]

Portofino answer and solutions rock. Low speed, injector servicing, exhaust to cockpit return due to design or aft weather and any of the possible leaks are not good if they worsen. Dirty lockers would be the last of my concerns. Recommend Terry Sunseekers in Adriano's first rate engineer.

 

[GarthP]

Thanks for everyone's input and especially Portofino's comprehensive response.

Exhaust arrangement is as Portofino described. However, the drain holes in the hull are separate from (but close to) the exhaust, so its simply back pressure under certain roll conditions.

Will post up any long term solution that gets implemented.

Cheers

Garth