Black water from exhaust at full throttle?

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Boeingdr

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Just got back from 3 superb weeks sailing the west coast. Used my trusty old Buch 20 quite a lot during transit north and south to Clyde as there wasnt much wind during these days. Never missed a beat however I did notice towards the end of the trip that when the throttle is put well forward (or backwards for reverse) the exhaust water became black (this was initially pointed out by somebody ashore).
Is this a problem? and what might cause it? the water clears as soon as throttle reduced.
 
Hmm, that would make a certain amount of sense as I replaced the original 2 blAded prop with a 3 bladed before last season. We did calculate the optimum for engine / gearbox etc with the prop manufacturer but it is a substantial increase in blade area.
Thanks
 
Boeingdr said:
Just got back from 3 superb weeks sailing the west coast. Used my trusty old Buch 20 quite a lot during transit north and south to Clyde as there wasnt much wind during these days. Never missed a beat however I did notice towards the end of the trip that when the throttle is put well forward (or backwards for reverse) the exhaust water became black (this was initially pointed out by somebody ashore).
Is this a problem? and what might cause it? the water clears as soon as throttle reduced.
Click to expand...

Black WATER is likely to be corrosion. Do you have a steel muffler?

Black SMOKE is most likely to be due to a fouled prop otherwise is likely to be a problem with your injectors -- or even your basic setup; though if it used to be fine then suspect injectors.

We need to know -- Black smoke, or black water?
 
black water could be a film of carbon on the surface of the sea; in which case it's likely to be partially burnt particulates, indicating a prop/engine power band mismatch.

An alternative is the muffler getting good and hot at sustained full revs, and clearing out carbon deposits which have built up at half throttle.
 
Could well be a choked air cleaner or spark arrestor. You're injecting max fuel into the cylinder without the corresponding oxygen to burn it all at high power lever settings, giving rise to soot particles.

Certainly the easiest and cheapest option to check on first.
 
Thanks for all the comments.
Discharged batteries with light fouling on the hull? could you explain that please.
The hull is likely to have light fouling but the batteries are well charged, but very interested in why that would cause black exhaust water.
Think I will start by investigating the exhaust elbow.
 
If the engine is being overloaded then there will be black smoke from the exhaust. An easy way to check is slowly increase the throttle setting if at some point the engine revs cease to increase but you still have some movement left on the throttle then the engine is overloaded. There could be a few reasons for this, the prop being too big, the prop getting growth over it, barnacles etc. Other reasons for black smoke is a blocked air intake filter or faulty injectors (doubtful).
If the exhaust elbow is blocked then the engine would probably run hotter, even to the point of getting an alarm. If you have run the engine at half load for prolonged periods then when you give it some wellie it tends to 'clean' out the combustion space but after a while the black deposits would clear.
Lots of options to think about, but always try the simple things first.
Hope this helps
Rgds
Bob
 
As bob said above.
Tthese engines do need a good clean out, I have on occassion had the "black water" but on closer investigation it has been carbon deposits (ie black smoke) in the water.
When I first got my boat I sufferd from this, I now make sure that I push the engine a bit harder each time I use it, and each time I get a little less black smoke at full throttle.
I put it down to the previous owners never giving it a good run.
I have the same problem with my car with its 2.5 TD engine, after weeks of town driving on short runs I give it a good blast to clean it out, only difference is with a car only exhaust comes out the back, with a boat, it gets mixed with the coolant water, if you give a boat diesel engine a good blast the amount of water flow also increases, so you will get more black smoke mixed with more water, and more deposits visible.
Well that is what I hope is the reason for my Black water (which as I said earlier is getting less every time I give it a good full throttle)
 
Black Water at Full Throttle

Smoke at full throttle is a sign that you are feeding in a bit too much fuel for the speed of the engine - boat fouling + larger prop mentioned + flatter batteries could do this.
Its not too serious as you can just throttle back a fraction until clearer water comes out while knowing that at any time you can get 100% of the power your setup can deliver at that time.
If it keeps on running extremely black then the exhaust elbow will begin to clog up and the injectors will get grubby - I once had the throttle at 100% while trying to head into a F7 in Southampton Water - it took 2 hours to get from Southampton to Hamble and the next time I tried to start the engine it was extremely reluctant until the injector was cleaned (quick careful scrape with Swiss Army knife screwdriver blade).
 
forethought said:
If it keeps on running extremely black then the exhaust elbow will begin to clog up and the injectors will get grubby - I once had the throttle at 100% while trying to head into a F7 in Southampton Water - it took 2 hours to get from Southampton to Hamble and the next time I tried to start the engine it was extremely reluctant until the injector was cleaned (quick careful scrape with Swiss Army knife screwdriver blade).
Click to expand...

Well I never did. I'd better get a Swiss Army knife.
 
forethought said:
the injector was cleaned (quick careful scrape with Swiss Army knife screwdriver blade).
Click to expand...



Very carefully I hope.....Invest in one of those wee brass brushes you find in B and Q and tn you can do it the way the professionals do.


I suspect the orinal posters problems are due to mild ovr propping and that some judicious trimming of the prop blades will gett the engine back to smokeless blackless full revs.

For his wondering , flat batteries means extra alternator load however this is more apparent on small one lung engines like the 1GM or MD2A where th alternator load can be a sizeable proportion of the total load.
 
Another vote for thorough check through the exhaust system - delaminated Vetus type exhaust pipe - looks fine outside but collapses from the inside blocking exhaust gases / raw water flow.
 
Boeingdr said:
....when the throttle is put well forward (or backwards for reverse) the exhaust water became black (this was initially pointed out by somebody ashore).
Is this a problem? and what might cause it? the water clears as soon as throttle reduced.
Click to expand...

Probably just the increased water / exhaust flow washing soot out of the system. give it a full throttle blast for ~1/2 an hour, and see if it's still coming out black. If so, the doom & gloom merchants above may be right, but I bet it'll be OK :)

Andy
 
If its just started, it may well be fouling on the hull and prop that has just 'tipped' over the resistance through the water, causing incomplete combustion. I had the same problem with an old engine - it did look like black water - a slick in the wake - but it was soot mixed with a good flow of exhaust water.

Try the simple things first like the air filter or the hull fouling.
 
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