Cummins Marine Diesel Repower Specialists Forums Cummins Marine Engines 480CE overpropped- what to tell prop shop?

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    Topic
  • #29976

    Nicholas
    Participant
    Engines: 1200hp Man d28 v12
    Location: Cocoa Beach, Fl
    Country: USA

    I’ve finally managed to get some visibility into my fuel burn numbers and from looking at Tony’s articles on propping the 480CE I can tell I’m overpropped. Looks like I need to reduce the fuel burn for each engine by about 2gph at 2200 RPM. Do ya’ll have a suggestion for how much pitch to have taken out to remedy the situation? They are 4-blade props (photo attached).

    Here are my numbers, measured with 4 people on board with gear and supplies for a 3 day trip, full fuel, full water, etc (I only have data from one engine, but I suspect they are the same or similar):

    1900 – 12.1 gal/hr
    1950 – 12.3 gal/hr
    2000 – 13.2 gal/hr
    2150 – 15.1 gal/hr
    2200 – 15.4-15.8 gal/hr (got two different measurements at different times & conditions)
    2300 – 17.7 gal/hr
    2350 – 18.3 gal/hr

Viewing 20 replies - 1 through 20 (of 31 total)
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  • #31315

    Philip
    Participant
    Vessel Name: 2007 35’ Cabo ‘FUGA’
    Engines: Cummins QSC8.3-540’s
    Location: Long Beach, CA

    As a matter of prudent maintenance, if there is a question about the lash it’s definitely worth double checking. Easy enough to do and only takes a few hours to go through the valves on both engines.

    Wether it’s a root cause of your different fuel burns, that would be interesting.

    Phil

    #31312

    Nicholas
    Participant
    Engines: 1200hp Man d28 v12
    Location: Cocoa Beach, Fl
    Country: USA

    Valve lash?

    Curious what you guys think chances are the issue could be attributed to valve lash needing to be adjusted? The port engine got new valves about 200 hours ago per PO records.

    #31310

    Philip
    Participant
    Vessel Name: 2007 35’ Cabo ‘FUGA’
    Engines: Cummins QSC8.3-540’s
    Location: Long Beach, CA

    For info, my fuel flows on my QSC8.3-540’s differ from 1-5% with the biggest difference right as I come over the hump and at max rpm the least difference. I have always attributed that to the counter rotation thru the transmissions. They will never be 100% matched so you will have to live with some differences.

    Your difference seems a bit higher, so it might be worth revisiting the props to ensure they are in fact matched. Also confirm no air leaks, good turbo inspections, and clean after coolers.

    Any vibration throughout the rpm range? If so maybe a misaligned or bent shaft/strut, wearing cutlass bearing, engine alignment, etc.

    Your going to have to just keep working your way through but good on you for dillegence and tenacity!

    Phil

    #31305

    William Walter
    Participant
    Vessel Name: Positive rate
    Engines: Cummings 480ce
    Location: Long island
    Country: Usa

    Fuel flow differs

    Not sure if you read through the thread of redoing my props..I was able to get the burns a lot closer then yours so you may still have an issue on that port engine.i definitely notice my port engine fuel burn is slightly higher.would be curious if all things being equal the port engine would burn more due to setup.

    #31089

    Nicholas
    Participant
    Engines: 1200hp Man d28 v12
    Location: Cocoa Beach, Fl
    Country: USA

    now with WOT numbers

    I went ahead and got numbers at WOT this weekend to go along with the cruise data I posted earlier. The variation was from going two different directions with regards to 25 kt winds and 3′ wind chop. Also my displays only show RPM in increments of 50, so I suspect it bouncing back and forth between 2650 and 2700 was indicative of the engines holding at the governed 2670 RPM max.

    Port: 2650-2700 RPM, 23.8-24.5 gph, 90-95% load , 29 psi boost.
    Starboard: 2650-2700 RPM, 22-23.3 gph, 86-89% load, 26 psi boost.

    Overall, it continues the trend of the port engine just seeming to be working harder to turn the same RPMs. One other interesting observation is that the Port engine is actually at or below the 450 diamond fuel burn curve at WOT, which was my WOT target point. At cruise RPM (2200), it was 14.4 gph vs the desired 13.6 gph.

    Still looking for suggestions of what to look at next. If nothing else, I’m going to try to shoot some temps with an IR gun when I can get someone else to run the boat for me, and when the bay is calm enough I won’t get killed in the engine room.

    #30802

    Nicholas
    Participant
    Engines: 1200hp Man d28 v12
    Location: Cocoa Beach, Fl
    Country: USA

    One more data point for any of ya’ll that are noodling on this…according to PO records about 2 years and 200 hours ago the port engine got a rebuilt head, new valves, new #6 piston/cylinder liner/rings/bearings, injector pump service, turbo rebuild, new injectors, and aftercooler service.

    The STBD engine got the same, except no piston/cylinder work and the valves were serviced (but not replaced) w/ new seals, and a portion of the exhaust pipe was rebuilt starting at the turbo outlet.

    So…to sum it all up, the port engine is burning about ~15% more fuel (with a corresponding higher load) throughout the operating range than the stbd engine, including at low RPM’s before the turbos spin up. Boost pressure is also a couple of psi higher at each RPM setting.

    The port engine received a more substantial overhaul than the stbd engine about 200 hours ago, including new valves.

    The boat has been running somewhat over propped for who knows how long. The port engine also had at least one prop blade bent pretty bad, such that the effective pitch of the port prop was about an inch less than the stbd. The props have since been reconditioned and re-pitched, such that the STBD engine is now very close to my target of ~13gph at 2200 RPM and the port is closer to 15gph. The scans show post-recon, the props match very closely.

    Prior to the prop job, black soot was beginning to accumulate on the stern. I haven’t noticed any in the ~20 hours I’ve run since. It’s been unseasonably cold here (in the 30’s-40’s) and i get a fair amount of white smoke at start and when I first throttle up. Pretty minimal although not zero smoke otherwise, and if anything the stbd seems to smoke a hair more than the port. I also get a bunch of white smoke if I throttle up to 1900 or so out of gear. Not sure if i’m even supposed to do that, but i only did it for a few seconds.

    Here are some possible explanations that have been suggested by others or by me, but I’m not sure what my next steps should be:

    -Intake leak – are the boost pressures indicative of a problem?
    -Valve adjustment – maybe the new valves on the port engine need a valve lash adjustment? Could that cause the discrepancy?
    -Port engine is counter rotating – this seems like it could drive single digit percentage differences in fuel burn and load but could it account for 15% difference?
    -Something stupid like a fuel filter? They were all replaced within the last 50-75 hours, and there are no signs on the fuel/water separators of any issues, but i guess it couldn’t hurt to change them anyway…
    -other ideas? Stop being so paranoid and just enjoy my boat???

    #30789

    Nicholas
    Participant
    Engines: 1200hp Man d28 v12
    Location: Cocoa Beach, Fl
    Country: USA

    Ok here are some new numbers. I couldn’t figure out how to get manifold temps. My displays showed no data for any of the exhaust temp fields. I certainly don’t see a smoking gun. Just seems the port engine is consistently working about 10-20% harder.

    1900 rpm
    Port fuel rate 11.5 gph
    Port engine load 53 %
    Port boost pressure 13 psi
    Port oil pressure 60 psi
    Port engine temp 156 F
    Port coolant pressure 22.5 psi

    Stbd fuel rate 9.3 gph
    Stbd engine load 41 %
    Stbd boost pressure 12psi
    Stbd oil pressure 57 psi
    Stb engine temp 159 F
    Stbd coolant pressure 22.5 psi

    2000 rpm
    Port fuel rate 12.6 gph
    Port engine load 57 %
    Port boost pressure 16 psi
    Port oil pressure 61 psi
    Port engine temp 156 F
    Port coolant pressure 22.5 psi

    Stbd fuel rate 10.6 gph
    Stbd engine load 45 %
    Stbd boost pressure 14 psi
    Stbd oil pressure 57 psi
    Stb engine temp 159 F
    Stbd coolant pressure 22.5 psi

    2200 rpm
    Port fuel rate 14.4 gph
    Port engine load 60 %
    Port boost pressure 21 psi
    Port oil pressure 65 psi
    Port engine temp 157 F
    Port coolant pressure 22.5 psi

    Stbd fuel rate 13.1 gph
    Stbd engine load 53 %
    Stbd boost pressure 19 psi
    Stbd oil pressure 58 psi
    Stb engine temp 161 F
    Stbd coolant pressure 22.5 psi

    2400rpm
    Port fuel rate 18 gph
    Port engine load 72 %
    Port boost pressure 27 psi
    Port oil pressure 64 psi
    Port engine temp 159 F
    Port coolant pressure 22.5 psi

    Stbd fuel rate 16.3 gph
    Stbd engine load 64 %
    Stbd boost pressure 24 psi
    Stbd oil pressure 56 psi
    Stb engine temp 163 F
    Stbd coolant pressure 22.5 psi

    #30685

    Nicholas
    Participant
    Engines: 1200hp Man d28 v12
    Location: Cocoa Beach, Fl
    Country: USA

    Transmissions are zf280-1a.

    Just to clarify – there is some uncertainty as to the fuel burn prior to re-propping. I only had visibility into gph data on the one engine, and when I refueled the boat the amount of fuel I added seemed reasonably consistent with doubling that total amount burned by the one engine – not a very precise validation.

    I didn’t get the visibility into both engines until after the prop job. It’s a long story how all that happened in that way. But I chose to take action immediately on the prop job, even when I was only half way through the ~900 mile trip home, because the numbers were so high and because I was beginning to see black soot accumulating.

    Also I’ll note that my fuel burn data is coming from the ECM, not from separate flow meters, if that matters.

    I’ll get more data hopefully this weekend

    #30602

    Philip
    Participant
    Vessel Name: 2007 35’ Cabo ‘FUGA’
    Engines: Cummins QSC8.3-540’s
    Location: Long Beach, CA

    Highly unlikely that an alternator or anything that spins on the front of the engine is the cause. But easy enough to check, and a good thing to check as well – simply remove the belt and spin by hand the alternator, all the pulleys and idlers and water pump etc. any play or roughness should be addressed.

    As for a no load rpm fuel burn – that data is not a good measure as without load your not really burning much fuel. Let’s get some boost and inlet manifold temps are cruise rpms and see if that shows anything….

    Keep in mind that pre prop adjustment you had +1/2” more pitch on one side that may have explained why the fuel burns were even before and now slightly different. What transmission are you running?

    Phil

    #30599

    Nicholas
    Participant
    Engines: 1200hp Man d28 v12
    Location: Cocoa Beach, Fl
    Country: USA

    Typing that response made me think of two items to post – no idea if they are helpful or not. First, the fuel burn is consistently higher (about the same percentage wise) throughout the entire operating range of the engine, including at low cruise RPMs and at idle. It’s even a hair higher at idle out of gear, although at zero load the burn is so low I’m not sure it’s accurate to a tenth of a gph or whatever the difference is. But this weekend I’ll try revving the engines up out of gear and see what the numbers look like. At least that will definitively rule out the running gear as the culprit.

    Only other thing is that I did have both alternators rebuilt right before I started the trip. The shop said they were pretty much shot when they opened them up. Totally random thought but makes me wonder if there is a spinning accessory on the port engine that is close to seizing up (or if the shop didn’t do a good job on the alternator??), if that would drive the higher burn. Seems like an awful large percentage load increase though to be something like that.

    #30598

    Nicholas
    Participant
    Engines: 1200hp Man d28 v12
    Location: Cocoa Beach, Fl
    Country: USA

    Ok I’ll configure the displays to show boost and also look for any signs of a leak. Any other measurements available from the ECM that I should be looking at to point toward potential culprits?

    #30597

    Philip
    Participant
    Vessel Name: 2007 35’ Cabo ‘FUGA’
    Engines: Cummins QSC8.3-540’s
    Location: Long Beach, CA

    Got to thinking some… what are your boost numbers? If you have a leaking hose in the intake between the turbo and engine you would have low boost and possibly higher fuel burns with little to no evidence of smoking unless you look really close. Especially this time of year after some cool temps those hose clamps all need a check. Get down there when running and look for an intake leak on the low boost engine.

    Just a thought

    Phil

    #30596

    Philip
    Participant
    Vessel Name: 2007 35’ Cabo ‘FUGA’
    Engines: Cummins QSC8.3-540’s
    Location: Long Beach, CA

    Typically if your engine alignment was out or had a prop shaft or strut bent you would have vibration. Shaft log can also account for different drag and thus different fuel burns.

    It’s normal to have some variance in fuel burns but you seem to have more than normal.

    I asked about maintenance and fuel filter as a small air leak could cause the fuel burns to be off. No idea if the high or low number is the right one….

    I’m sure others will have a next step….

    Phil

    #30592

    Dave Carlson
    Participant
    Vessel Name: Bec'n Me
    Engines: 500 QSC
    Location: Fort Myers
    Country: USA

    I had a similar problem on a Searay with these engines. It was over propped by two inches of pitch. During the process I installed egt/boost guages as per Tony’s recommendation. After the props were done the boat actually picked up speed in the mid range and the exhaust temps went from over 900 at cruise to 700-725 and the boost was the same on both engines. It still had a variation on fuel burn as described above. I even had a quality Cummins mechanic come down to check the electronics etc. while running at speed. He told me to quit being so anal, there was nothing wrong with my boat, it is just an algorithm!

    I took his advice and since the egts were so good I ran the boat from Fort Myers to Key West with the generator off. At fill up the two tanks were not off more than 5 gallons. I used the boat for 2 more years (100-125 hrs per year) with no problems and what I considered to be good fuel consumption and good speed in the 2150-2200 RPM range.

    I should mention when this work was being done the cooling/air system was done following the “West Coast”
    protocol!

    #30562

    Nicholas
    Participant
    Engines: 1200hp Man d28 v12
    Location: Cocoa Beach, Fl
    Country: USA

    Just wondering…is a shaft alignment issue a likely culprit to explain the difference in fuel burn? I’m just wondering because if the prop technician was right, and one or both of the props had run through a sandbar, would that also likely have thrown the shaft/engine out of alignment as well, and could that lead to a ~10-15% higher fuel burn at a given RPM on one side?

    #30558

    Nicholas
    Participant
    Engines: 1200hp Man d28 v12
    Location: Cocoa Beach, Fl
    Country: USA

    Looks like a nice prop job.

    Any chance you did any other maintenance while the props were at the shop? Change fuel filter by chance?

    Phil

    Nothing on the engines. I had a hydraulic leak on the steering fixed. The primary and secondary fuel filters were replaced when I took delivery of the boat. I’d say they have ~60 hours on them. It’d be easy enough to replace them though if they are even somewhat likely to be a driver here.

    #30555

    Philip
    Participant
    Vessel Name: 2007 35’ Cabo ‘FUGA’
    Engines: Cummins QSC8.3-540’s
    Location: Long Beach, CA

    Looks like a nice prop job.

    Any chance you did any other maintenance while the props were at the shop? Change fuel filter by chance?

    Phil

    #30544

    Nicholas
    Participant
    Engines: 1200hp Man d28 v12
    Location: Cocoa Beach, Fl
    Country: USA

    Attached are the prop scans, both before and after. Admittedly, I’m no expert in reading such things but I don’t see anything that would explain the ~10-15% difference in fuel burn between the two engines at any given RPM. Any thoughts?

    #30441

    Nicholas
    Participant
    Engines: 1200hp Man d28 v12
    Location: Cocoa Beach, Fl
    Country: USA

    To answer robs q – the port engine, which is the higher fuel burn engine, is the one I had fuel data on pre prop rework

    Re:Philip – I have scans but they are hard copy only. I’ll take a photo of them and post them shortly.

    #30424

    Philip
    Participant
    Vessel Name: 2007 35’ Cabo ‘FUGA’
    Engines: Cummins QSC8.3-540’s
    Location: Long Beach, CA

    What kind of prop job did you get? A traditional pitch block adjustment or the newer prop scan style with pitch and balance computer reports?

    If the latter prop scan style can you post prep and post adjustment printouts?

Viewing 20 replies - 1 through 20 (of 31 total)

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