3 blade prop

[maybetuezday]

We just purchased a 2004 Hunter 36. New to sailing. We were having problems under power at 2500 rpms with smoke and fumes coming from our engine. We were first told it was our belts and we had those replaced. However the same problem. We have a 27 hp Yanmar. We were then told that it was our prop. That we could not have it up to 2500 with out burning oil. We have a 3 blade bronze Brunton's auto prop. We were told we would be able to raise the power and speed of our boat if we switched to a fixed prop. Does any of this sound right to anyone? I am not sure why we can't be under power at 2500 rpms when the engine is rated around 28 or 29 just because we have that kind of prop. Please help!!!

[my900ss]

Ok, so let me politely say that you should stop listening to whomever is currently giving you mechanical advice. They are effectively telling you that if your car engine was smoking replace the tires...

A few questions for you.

1. Where is the smoke originating from? I.E. the exhaust output or somewhere in the engine bay?

2. What sort of fumes? I.E. diesel fumes, burned oil fumes?

3. Where are the fumes most evident? I.E. Topside, below decks, engine bay etc.

4. Is the issue digital in nature i.e. at 2,400RPMs there are no fumes and no smoke, yet at 2,500RPM's you have the smoke and fumes? I.E. below 2,500RPM's do you have any issues?

5. Noise... is there any noise associated with the smoke and fumes?

6. Is there any separation between what is generating the fumes and smoke?

7. What color is the smoke?

Have you contacted Yanmar with the same question as posted on sailnet?

Regards,

T

[maybetuezday]

smoke is coming from companionway. Fumes start first and then smoke, as soon as we turn down the throttle it stops immediately. There is no noise when this happens. The smoke is white to grey not black. The fumes smell like fumes as opposed to burning oil. When it has happened we turn the throttle down right away so we really haven't studied the effects in detail and no we have not contacted yanmar but we will.

[nemier]

Hello Tuesday.
Have you or anyone else changed the oil lately?
And if so, make sure it is not overfilled!
I once overfilled the oil on my Catalina 36 and had the same problems under load. When we arrived at our destination I removed a liter. Next time under load, no issues.
It's worth telling you that according to the dipstick, it was near full, not right at 'full'. I now operate at a dipstick level of no more than 3/4 full. Never had an issue since.

[Minnewaska]

Exhaust leak? Steam pushing through at higher RPM/temps?

[T37Chef]

Originally Posted by Minnewaska

Exhaust leak? Steam pushing through at higher RPM/temps?

That would be my guess...check the elbow connection?

[maybetuezday]

We bought the boat in August and took it from Havre de Grace to Rock Hall. 5 hour trip, no problems. We took it out a few times after that..no problems. Had the oils changed and filters. Took it out and when we turned up the throttle I could smell fumes coming from the companionway. I asked my husband to turn it down because of the fumes and didn't know what the problem was. As soon as the throttle came down the fumes went away. A little while later he throttled up again and again fumes and then smoke. I told him he needed to turn it down and I went to check to make sure we didn't have a fire. Again, once turned down everything went away. We had two seperate mechanics come by and each one of them ran it full throttle in the slip and they could not replicate the problem. One changed the belts and one lowered the oil level because it was too high. When taking it to the marina for winter storage (and with an employee from the marina) we had to give it more throttle because the tide was out and we were scraping bottom and needed to avoid coming aground. When we did this the fumes and smoke started again. The marina then asked me what the engine topped out at? When I asked our surveyor he said usually the 27hp yanmar would be 28 or 29 but the with 3 blad auto prop we have it's around 23. He said after that point we are just running the engine too high and burning oil. When I told this to the marina they think maybe the prop needs to be fixed and they would take it off and send it out. With my ignorance of sail boats I can't imagine that a prop would be doing all that and so I would say then get rid of the prop and put a fixed prop on. So now I don't know if it's the prop, an engine problem or with my 36 hunter I can't go any faster than 2300 rpms which doesn't make much sense because that is really slow. I still ahve no answers and I know that when spring comes I am still going to have the problem. But what really is the problem??

[PalmettoSailor]

First, I'd highly recommend you check the exhaust system for any leaks and equip your boat with a Carbon Monoxide detector.

I think one other potential cause of smoke from the engine compartment, could be leaky injectors. If fuel is entering the cylinders at the incorrect times, partially burned fumes might escape back through the open intake valves and out the breather.

Whatever it is, a good diesel guy should be able to diagnose it and fix it. These engines are pretty simple and reliable and will run for decades with relatively miminal maintenance. From what you've said about the person you've spoken to regarding your issue, I don't think you've found a good diesel guy yet. Ask around the marina, find out if there are any delivery captains around and talk to them about who they recommend.

Edited to to add:

Regarding props, keep in mind that engines develop their rated horsepower at a specific RPM. If for example your engine is rated at 27HP at 2800 RPM, you need to select a prop that will allow the engine to reach 2800 RPM. If the prop is too large or has too much pitch the engine cannot reach its rated RPM and will not produce full power. Its like driving a car in 4th gear up a hill, the engine is straining and fuel is being wasted. In a car, you downshift, with a boat you might need to select a different pitch for the prop.

That said, I don't think the prop is the problem your seeing or at least not all of it. A boat that's over-propped will usually indicated it by 1. Not reaching rated RPM, 2. Black/Dark smoke from the exhaust, 3. Running hot when pushed.

[maybetuezday]

Thank you for your response. We do have carbon detectors on the boat and they have not gone off. I will check around with a mechanic (we have one who is also a Yanmar distributor in the area and go that route. So you are leaning more to the engine as being the problem rather than the prop?

[rayncyn51]

A prop that is too large for the engine and weight of the boat will limit the engine's max rpm at wide open throttle. If you try to push the engine past that max rpm, it will act as you are describing. The most efficinet rpm for cruising on any given boat will be somewhat less than full throttle. Anything above that rpm will not make the boat go faster, it will just cook the engine.