Easy Drawing of a Boat With Black Smoke
- #1
Our 4108 has always been great with no smoke.
Since arriving in Spain we had an issue with dirty fuel. This was black discolouration which would not settle out at all. Nor would it clear after many passes through my polisher. There was no bug present but the dip stick had a heavier coat of tar like stuff than previously. We thought that a precautionary bug treatment we had used had worked but left a fine residue. The advice on line was that these black particles are very fine and will pass harmlessly through the engine!
Back on the boat and preparing for sailing I tested the engine. It revs freely up to 3500 rpm but under load Maximises at 2500 with black smoke this is tied up.
The hull and prop don't look to be badly fouled.
Tomorrow we will be lifted and jet washed and clean the prop (18" x10pitch)
We will run the test again and check hull speed at various revs
I suspect that the injectors may be fouled.
I have spares on board and plan to have them serviced and fitted.
I will value your opinions and advice on this.
- #2
Aja
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- 6 Nov 2001
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If you were tied to the pontoon/Dock when you tried revving the engine in gear, it doesn't matter whether the hull is clean or not. Can't help you with the real problem though ��
Regards
Donald
- #3
I wouldn't bother messing with the injectors until you have given it a few bursts up and down to maximum revs in neutral and then a short blast at max revs in gear in open sea to see if that clears it.
Just don't mention the home of pasta. 
Richard
- #4
Black smoke where none was present before plus limited revs may be caused by a fouled exhaust elbow. Should be easy enough to check and clear if required. I'd do that before messing about with the injectors.
- #5
As above. It's usual not to be able to make max revs in gear whilst parked. The result is over-fuelling = black smoke (as you'd get if substantially over-propped).
- #6
Heckler
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- 24 Feb 2003
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- 15,846
Our 4108 has always been great with no smoke.
Since arriving in Spain we had an issue with dirty fuel. This was black discolouration which would not settle out at all. Nor would it clear after many passes through my polisher. There was no bug present but the dip stick had a heavier coat of tar like stuff than previously. We thought that a precautionary bug treatment we had used had worked but left a fine residue. The advice on line was that these black particles are very fine and will pass harmlessly through the engine!Back on the boat and preparing for sailing I tested the engine. It revs freely up to 3500 rpm but under load Maximises at 2500 with black smoke this is tied up.
The hull and prop don't look to be badly fouled.
Tomorrow we will be lifted and jet washed and clean the prop (18" x10pitch)
We will run the test again and check hull speed at various revs
I suspect that the injectors may be fouled.
I have spares on board and plan to have them serviced and fitted.
I will value your opinions and advice on this.
Ref a few of my posts recently. "Full throttle"position opens up the fuel rack to maximum fuel. If the engine doesnt hit max revs, the governor keeps the rack fully open and with no max revs, not enough air sucked in and so black smoke. Its not your injectors! Revving it tied to the pontoon is not a good test, the prop cant atain max revs because the water flow is not helping it, ie no forward motion. If you do the same test under way then you will get more revs, the engine atains its revs, the governor shuts the rack a bit and happiness! I suspect your prop has some fouling which wont help either.
01978 860 eight three two if you want to chat.
Stu
- #7
lw395
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- 16 May 2007
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- 42,084
Probably right.
Could only be injectors if they are fouled and giving a bad spray pattern I think?
It's useful to know what your engine will do tied to the quay, so you can see what's changed.
Some boats will get close to max revs while hard aground, others nowhere near.
So not a good test unless you have prior knowledge of what it used to do.
- #8
Thanks Stu and all. Good advice as always.
Went out for a test drive and things were much better! Jet washed hull and cleaned prop, 7knots at 2600 and only smoke visible when attempting more speed/revs
It is a useful point that the tied up test is only any good for comparison.
Thanks everyone again!!
- #9
Tranona
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That is very much overpropped - which seems to be common with 4/108s as they are often too powerful for the boat. They are rated at various levels up to around 50hp by limiting the revs.
You are only drawing about 30hp at 2600, even though your engine is governed to 3500 and probably 42hp. The limitation for you is the propeller which is right for the boat as you can achieve hull speed. However, you are not able to use the rated hp of the engine so you have little in reserve for adverse conditions. A smaller prop would increase the revs of the engine and improve performance against wind and waves.
- #10
Heckler
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That is very much overpropped - which seems to be common with 4/108s as they are often too powerful for the boat. They are rated at various levels up to around 50hp by limiting the revs.
You are only drawing about 30hp at 2600, even though your engine is governed to 3500 and probably 42hp. The limitation for you is the propeller which is right for the boat as you can achieve hull speed. However, you are not able to use the rated hp of the engine so you have little in reserve for adverse conditions. A smaller prop would increase the revs of the engine and improve performance against wind and waves.
Not arguing but some useful practical info. My Bene 381 has a 50 hp MD22. The previous owner has also changed the prop to a 16 by 16.
1800 revs gives about 6 kts in calmish water, 2100 gives the same in rough water. Before I put the in the shaft spacer and changed the engine mounts, any more and the shaft started to vibrate which offended my mechanical sensibilities. Having been on friends boats they seem to ignore what I consider to be vibration. Since doing the work I can hit over 3000 revs and get up to 8kts. When I first did the work and tested tied to the pontoon I could only get 2800 rpm with quite a bit of smoke. That is how I discovered that tied up and free running gives different results.
Going on from there we escaped from Padstow a while back after a few days sheltering from bad weather. As we left Doom Bar behind the remaining swells coming in were quite short and high. I foolishly thought that big engine and more power would get us out of trouble, in fact all it did was launch the nose at the sky and slam us down after the crest of the wave. The realisation hit that power alone doesnt get you out of trouble. Judicious use of reefed sails and low revs combined to get us moving in a more kindly manner.
- #11
That is very much overpropped - which seems to be common with 4/108s as they are often too powerful for the boat. They are rated at various levels up to around 50hp by limiting the revs.
You are only drawing about 30hp at 2600, even though your engine is governed to 3500 and probably 42hp. The limitation for you is the propeller which is right for the boat as you can achieve hull speed. However, you are not able to use the rated hp of the engine so you have little in reserve for adverse conditions. A smaller prop would increase the revs of the engine and improve performance against wind and waves.
Thanks for the steer on that, my existing prop is 18" x 10 pitch (just confirmed) what would be suggested and would this mean higher revs to achieve my desired cruising speed. Currently this is 1700 to achieve 5.5. as we increase to 1800 or 1900 the engine sounds slightly less pleasant, not noisy or stressed but noticibly different. We like the sound at 1700!!
Thanks all again.
- #12
I think that we have communicated before and that you are a fellow Neptunian owner. I'm surprised that you have only recently had problems with a smokey transom, every Neptunian I have seen has suffered from a dirty transom and we are no exception. I believe that part of the problem is that the Perkins 4108 is a noisy beast and the more revs that you give it the noisier it gets. As a consequence owners have over propped the boat in order to achieve 6kts or so at lower revs, which has meant that the throttle level has to be advanced further than it was designed to be and you end up with smoke from the unburnt fuel. Though this does not explain why it has suddenly happened to you.
Our experience is as follows. When we brought the boat it had a fixed three bladed prop', sorry I can't remember the size, but it was of significant proportions given the size of the boat. 1500 rpm gave us 6kts and a dirty transom every time. One fellow owner saw ours and suggested that we followed his example and painted the transom in a dark colour, as he had had to.
Our prop had a nasty nick in one of the blades and we lashed out on a brand new Kiwi feathering prop. On the Kiwi prop it is easy to adjust the pitch, so we started with a coarse pitch, but following discussions with my friendly engineer we did some calculations which suggested that we reduce the pitch, but the down side was that the revs would have to come up in order to achieve 6kts; at one time we were considering a setting which would have required 3200rpm. Believe me the noise was incredible! We have compromised and settled on a setting which requires 2200rpm. The result was minimal soot on the transom, but it cannot be described as soot free.
We have had a top end overall on our 4108, as a result of a failed exhaust elbow, which involved in having the injectors serviced. The result was a slightly cleaner transom, but it's not perfect by any means. My tame engineer tells me to remember that the engine was designed in the 1960's when diesels were expected to smoke, and that is unfair to try to compare them to more modern designs.
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- #13
I learned that lesson in the Sound of Jura recently. Throttling back made it much more comfortable and less scary.
Source: https://forums.ybw.com/index.php?threads%2Fblack-smoke-under-load.486301%2F