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Carver 570 w/ Cummins 535 HP missing 200 RPMs

Discussion in 'Carver Yacht' started by Aquaventures, Aug 21, 2006.

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  1. Aquaventures, Aug 21, 2006
    #1
    Aquaventures

    Aquaventures New Member

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    I am trying to solve a problem on a 2001 Carver 570 Voyager with 535 HP Cummins QSM 11 motors. These motors are supposed to acheive 2300 RPM at full throttle. On a trial run 2100 RPM was the max with a speed of 22 knots. Seas were 1-2 feet and wind was light. The hull is clean as are the props and running gear. The motors do not smoke at all even from a "hole shot"; indeed they are two of the nicest running motors that I have seen. There is 800 gallons of aged diesel in the tanks (full fuel). We are changing primary and secondary fuel filters as well as air filters. We are also polishing the fuel. We will run again when this is done and if there is no improvement we plan to have a Cummins tech go out with us with his computer to check engine loads and settings. My question is this: Would the additional weight of full fuel (say 5600 lbs) be enough to drag the RPMs down this much? Is the ageing of the fuel a contributing factor? Would a fuel additive improve the performance?
    There is also full canvas on the flybridge which may be contributing drag from the "sail" area. We believe that the propellors are pitched correctly. Our trial run was done with the air temp around 90 degrees and high humidity (Ft. Lauderdale). Removing the old fuel is not something that we want to do since the boat is to be delivered some 1200 miles from here and fuel is so expensive. Is it possible that the fuel weight, old fuel, the resistance from the canvas and the enviromental conditions could all contribute together for a 200 RPM loss? Would it be advisable to get the Cummins tech out first? Does anyone have experience with this boat/motor package to tell me if this is normal based on the conditions described. If so does the boat get faster (and RPMs higher) as the boat gets lighter? Does Carver set these boats up to do 2300 RPMs in a light boat condition? Any input is appreciated. RK
  2. Garry Hartshorn, Aug 21, 2006
    #2
    Garry Hartshorn

    Garry Hartshorn Senior Member

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    Bottom line is it require more power or less resistance to achive that rpm. you need to acheive one or more of the following

    less pitch
    smaller diameter props
    less blade area
    reduce weight of vessel
    reduce windage
    reduce underwater drag
    more power

    What did the vessel achieve in prior seatrials ? is this a new issue or an ongoing one ?
  3. CaptTom, Aug 21, 2006
    #3
    CaptTom

    CaptTom Senior Member

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    Aquaventures,
    The full canvas could impact speed/rpm but I don't think by that much. What is the coolant temp when you're running? Normal or to cold/hot? You say there's no smoke and the hull is clean, but how many hours on the engines? Maybe the soot was cleaned off and the fuel pump leaned out to stop the smoke, which is now giving you less than expected RPM.
    It can't hurt to polish the fuel if it's been sitting, but that alone will not help the RPM. How old is the diesel, over a year? If that was the problem then many more yachts around Ft Lauderdale would have the same conditions. Perhaps the boat is heavier than you think, as in a wet bottom. You say it's traveling 1200 miles soon, which way north or south? If north, it will get there, be fueled up and sit over the winter, possibly with same problem as now. Have the Cummins tech check the fuel flow/capacity. Low fuel flow will slow you down with no smoke signs at the exhaust since it's starving for more fuel.
    Good luck.
    Capt Tom
  4. K1W1, Aug 22, 2006
    #4
    K1W1

    K1W1 Senior Member

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    Hi,

    Where did this figure come from?

    You can bet your bottom dollar that the manufacturer did not run it on test for max speed and performance with the tanks pressed up.

    Loading of any high speed vesel is critical to the overall performance.

    There are a number of things that you could ask the Cuimmuns Tech to check.

    I am not familiar with this exact engine so I don't want to suggest things that could have an influence just tell the Cummins agaent before the mechanic is sent out that you want him to check for reduced top end so any special tools will be brought to the job first time.

    Do you have any confirmation that the Props are pitched correctly?

    I hope you get this sorted out successfully and please post back with the outcome so the rest of us can add another open ended question to our knowledge banks list of answers!
  5. TSI AV, Aug 22, 2006
    #5
    TSI AV

    TSI AV Senior Member

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    Hi,

    1. 2100 rpm. True / false value ?
    Sometimes indicators show not correct values.
    Make it sure with independent measuring device.

    2. Is the fuel rack at the limit ? Or somebody changed that limit ?

    3. Engine is overloaded or not ?
    Exhaust temp; Fuel rack; Turbo speed;
    (Compare to shoptest data).

    4. Input signal (mech.,pneumo,electr.,etc.) to the governor is not correct.

    5. Governor is not performing well.
    Probably, this type of governor has an separate oil filter.
    Replace it, if so.

    6. Is this type of engine equipped with injectors-pumps, driven from camshaft (by pushrods) ?

    But first - check rpm in fact !

    Regards,

    Andrei
  6. Aquaventures, Aug 22, 2006
    #6
    Aquaventures

    Aquaventures New Member

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    Thanks for the response Andrei - Your point is well taken regarding the verification of actual RPMs. Kind Regards, Richard
  7. Aquaventures, Aug 22, 2006
    #7
    Aquaventures

    Aquaventures New Member

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    Hi K1W1, Thanks for the input. We have decided to have a Cummins tech with us for seatrial Friday. 2300 RPM is the manufacturers max RPM figure. I am pretty sure that the boats are initially tested in a light load condition. I am more and more inclined to believe that the full fuel load is what is reducing RPMs. I don't want to repitch the props because in a light load condition it very well may be close to 2300 RPM. I am hoping that someone reading this forum has already been down this road with the same boat/engine package and can verify that the boat will indeed show a significant RPM increase in a light load condition. Kind Regards, Richard
  8. Aquaventures, Aug 22, 2006
    #8
    Aquaventures

    Aquaventures New Member

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    Hi Capt. Tom, The motors have 180 hours total. Coolant temp guage shows normal temp. We will have the fuel flow checked. The diesel fuel is over 1 year. Your point regarding hull weight is well taken. Hopefully there is no moisture in the hull but we will check at survey. Kind Regards, Richard
  9. Aquaventures, Aug 22, 2006
    #9
    Aquaventures

    Aquaventures New Member

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    Hi Gary, I agree with you that these items are all related to vessel performance. I am coming into this without information on prior history. I will have more information when we sea trial Friday. I am suspecting that the fuel load is the main performance variable in this situation. Thanks for your input. Kind Regards, Richard
  10. Garry Hartshorn, Aug 22, 2006
    #10
    Garry Hartshorn

    Garry Hartshorn Senior Member

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    Best of luck, hopefully it is an easy one
  11. TSI AV, Sep 16, 2006
    #11
    TSI AV

    TSI AV Senior Member

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    Hi again,

    Aquaventure, any "happy end"s ?

    "We" are waiting impatiently...

    Rgds,

    Andrei
  12. Aquaventures, Sep 18, 2006
    #12
    Aquaventures

    Aquaventures New Member

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    Conclusion of 200 RPMs missing.

    The primary factor seemed to be weight. When we took 400 gallons (2800 lbs) of fuel off of the boat the RPMs increased by 100. The motors seem to be running just fine. Fine tuning the props would be the next logical move. The boat has been sold and is currently underway to the new owner in TN. Thanks for your interest.