What's this nozzle for ??

My little diesel GRP boat has this funny little nozzle attached to the thu hull of the engine exhaust >>



Does anyone know what's it for ?

Exhaust block on MD2B sits one foot above the waterline, so anti-backflow seems not the reason.

 

I've seen extensions like that to keep soot away from the hull.

 

An attempt by previous owner to keep water from backing up exhaust tube when backing up the boat or waves forcing water up into exhaust tubing. Really not an issue if the engine is running.

Pointing up will collect some rain? Have you considered putting this through the hull under the water? I wonder myself about underwater exhaust, having the exhaust exit under the water.
Certainly then no diesel soot on boat, and much less diesel exhaust smells, less CO and pollution for you to breathe.

I was thinking a contoured or angled pipe type through hull, as long as you can not reverse siphon, so might have to have a small exhaust air hole above the water?

 

Many Thanks guys !
I actually hate this ugly little appendix, but hesitated to do something thinking it has to be there for some (important) reason, although I never see them on other boats.
Since the opening points upwards, it dirties the stern deck with soot/diesel.

Tried turning the opening downwards some time, but it didn't move and so gave up being afraid to damage the sealing: not clear how its fixed to the thru hull.

As I understand it has hardly any anti-backflow effect, so I'm considering either sawing the opening to make it point sideways, or sawing it off all together.