QSC540s showing different load %

[ph321]

Hi,

I was hoping that someone might be able to help with where to look to solve an issue I’ve got with the port QSC540 showing higher fuel burn & load percentages at the same RPMs.

Late last year I had the props re-pitched and a full salt water service. Aftercoolers and everything removed and cleaned. The before scan of the props showed that the port prop had ½” less pitch than the starboard, whether it left the factory like this or has been adjusted in the past 12 years to hide an issue I’m not sure. The prop shop is certain they didn’t make any mistakes… To me, all symptoms look like the port engine is seeing more load.

Other points which may be relevant:

– If I bring the revs up to say 2000rpm and then push the throttles fully forward the port engine lags the starboard.
– Temperature seems to run slightly higher on the port engine at cruise speed
– No noticeable smoke at any rpms. Idles smooth.
– Air filters are new (Walker AirSeps)
– I haven’t had the riser off the turbo yet to check the exhaust housing but the port engine uses more fuel / shows higher load both on & off boost.

The boat is due to come out for an anti-foul again in August so I’ll probably get the props scanned to make sure they are the same. Is there anything I should check with the engine beforehand? 

Fuel burn on the graph is shown in L/hr. 

Paul

Topic

[ph321]

Tony,

Thank you for taking the time to reply.

1. I’m OK with this and had the props repitched last time the boat was out of the water. If both engines were showing the results that the starboard engine is I would be 6L/hr below the Cummins fuel graph at 2300rpm where I cruise. This was admittedly with new anti-foul but otherwise as heavy as it will ever be.

2. Noted. It looks like I’ll take the port prop back and get them to take another 0.5″ off.

3. Noted.

4. There is a vacuum guage on the racors and it’s reading doesn’t change as the revs increase. Should I check after the on-engine filter (also new)? Could I just swap the pressure sensors on the fuel rail to see if that affects any of the readings?

5. It’s true I would probably prefer the boat went faster. Having said that, I am part way through trying to get the props correct.

Thanks again for your help.

Paul

[Tony Athens]

Paul,

I am going to give my 2-cents worth here……

1) It’s 100% IMPOSSIBLE to under prop your engines or any engine of this type .. You can only OVER PROP THEM..   Just think about that for a while..

2) Props shops can be really good as to “shaping”  a prop to get what you need, but the problem is,  I have never found one shop that “knows”  what you need–And I am talking 100’s of prop adjustments over 30 yrs  and not less than 10 shops.. YOU and only you need to TELL THEM what you need to do based on what you have now.  All they seem to think,  and maybe are trained to do,   is WOT RPM vs HP vs the vessel specs…………………..Ask yourself this:  Do you know anyone that runs around at WOT in the normal course of a day on the ocean? Something else to think about.

3) Per Cummins engine  design, +/- 5%  on  all performance #’s are within standard tolerance..

4)  Ever measure fuel VACUUM at the inlet to the engine?  That “number” alone can affect the read-out as to  the “load %” and “GPH”.. Remember, both of these numbers are “algorithms” based on various reading, with “feul inlet vacuum being a big one… 

5) the fact that you are over-propped at your “cruise RPM’s” tells me that you will never be happy with overall performance.. Remember #1..

Let’s start with this and some thinking by you and who ever else may be reading..

Tony

 

 

[ph321]

I wasn’t really given a choice by the prop shop to keep the difference. I just asked them to take about an inch of pitch off and they gave them back nearly identical. The fuel burns were pretty close beforehand. Is it common for manufacturers to have to put different props on identical engines? Transmissions are ZF285IV with 1.815 ratio.

Engines have about 800hrs and otherwise seem healthy. I don’t have any great photos unfortunately, it’s pretty tight in there. The exhaust risers are still original and are the “doomed to fail” style, they’re on the list to do soon but no signs that they’ve failed yet. Fuel filters were replaced at the time with no difference in load/fuel burn.  I usually cruise at 2300-2350rpms where both engines are below the Cummins’ fuel curve.

Sounds like I should just get half an inch taken off the port prop next time it’s out. I just didn’t see the point in doing this if it was just hiding other issues. 

Thanks,
Paul

[Rob Schepis]

You didn’t include load% in your graph…

So it sounds like you assumed the less pitch in the port prop was in error and you had the props re-pitched identically?  Were the fuel burn’s in line with one another before you added pitch to the port prop?  It is common for a twin engine boat to load the engine’s differently hence that lower pitch in the port prop was possibly/probably meant to be there.  The port side could have more in the gearbox to spin as well.  What tranny’s and what ratios?  You want to be <66LPH at 2,200rpms…the port side is overloaded.  Fuel filters all clean?  Any pictures of the engines and exhausts?

[Author]

Replies