Any chemists among you?

[CDK]

When I open the engine bay of my boat, I smell something acid.
The boat is not in use because I am working (again) on various electronic items.
Batteries are of the sealed type, all 3 of them full and kept that way by a small solar panel, so I've ruled them out.
There is still a trickle of seawater coming in because of a laminate fault somewhere on the transom; is is pumped out automatically, but the pump cannot expel the last 1,5 inches. On top of the water is an oil film from one of the diesels, it drips some engine oil from the turbocharger although the ring nut is as tight as I dare pull it. There also leaks a minimal amount of diesel fuel from one of the injection pumps where a seal is not 100% and there may also be some fumes that escape from the oil pan ventilation. All in all, the oil film kind of seals off the water surface so the engines cannot corrode from evaporating sea water. But the smell is always there....

[SamSam]

I would check the condition of the batteries. A charger on a bad battery stinks like something toxic.

[CDK]

The sealed batteries have these "eyes", green is OK, black is discharged, white is end of life. they are all green.

[TeddyDiver]

And leaking battery stinks..

[CDK]

Since there was little feedback on this forum, I posted my question on a usenet forum (sci.chem) and received several response. This one, from Ron Jones in the UK, makes a lot of sense to me.
In the meantime I had my wife stick her head down the engine bay hatch. She disagrees with me and says the smell is more like - but not exactly - H2S. That is the smell of rotten eggs...

> OK, so I'm not the only one. My nose registers an unpleasant odor but
> has proven to be totally unreliable as a sensor: I translate it as
> acid or acrid.
> Diesel fuel is said to contain sulphur, probably as SO2. They also
> sell low-sulphur diesel at a higher price so it probably is true.
> With water it forms H2SO3 which may be what I smell. But that would
> mean that the fuel must also react with the metal parts it comes into
> contact with.

It's not there as SO2, the sulphur is there as thiols - hence the typical
diesel smell. Having said that, bacterial oxidation could well turn these
into some odour that seems acidic. The mix of diesel + water *is* well
known to be attacked with bacteria - it definitely has been known to cause
problems in boat fuel tanks where water separates out and bacteria goes
causing a growth that can later block the fuel filter (BTW that's why I
always add FuelSet to my boat's diesel, and keep the tank as full as
practicable - prevents too much air being drawn in with temperature changes
and causing condensation in the tank).

--
Ron Jones
Process Safety & Development Specialist
Don't repeat history, unreported chemical lab/plant near misses at
http://www.crhf.org.uk Only two things are certain: The universe and
human stupidity; and I'm not certain about the universe. ~ Albert
Einstein

[longliner45]

rotten egg smell is from overcharged batterys,,do you leave a trickle charge on while you are gone?? or is the smell more prevalent when running?..I would dissconect the batterys for a day and see if the smell persist,,hope that helps ,longliner

[longliner45]

well?

[CDK]

I've pumped the bilge dry. The water + diesel had thickened from bacterial growth and smelled terribly.
To prevent this from happening again, I added some chlorine to the bilge water.

[FAST FRED]

An easier plan is better bacteria. There are many marine bacteria starter setups that are designed to EAT all the oil in the water.

Big help in places where the "Sheen Police" are active and want thou$and$ for every bilge pump run .

FF

[Itchy&Scratchy]

Could be the water that you say is trickling from the laminate, stagnant water trapped in between the layers can cause a bad smell, like when you open up an osmosis bubble.

cheers
Justin

[ancient kayaker]

Wet rust smells acid ...

You can get a Ph test kit as used for swimming pools, if the Ph is lower than 7.5 it's acid

[CDK]

Originally Posted by FAST FRED

An easier plan is better bacteria. There are many marine bacteria starter setups that are designed to EAT all the oil in the water.

Big help in places where the "Sheen Police" are active and want thou$and$ for every bilge pump run .

FF

Most of what Google found for me were theoretical discussions plus some bacterial starters for aquarium applications. Do you know any commercially available oil eating cultures?
"ancient kayaker": This is the Adriatic sea, the Ph needs not to be tested as it is always under 7.5. With more than 2% NaCl and lots of other chemicals in the water even marine grade stainless steel has a reduce lifespan here.

[ancient kayaker]

The Ph of the fluid in the engine bay may not be the same as the sea's unless the Adriatic is even more poluted than it's reputation. Is it possible to remove or wrap the batteries? That might isolate the source of the smell. Good luck with your enquiries wherever they lead.