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12v71 Detroit Diesel Govenro Shim Spec

Discussion in 'Engines' started by CaptOz, May 20, 2016.

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  1. Robertoman

    Robertoman Member

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    I just went thru the whole process you are going thru with 6V92's. After everything, the problem was air in the Hynautic hydraulic throttle controls which would provide full throttle in all phases of governor control except under LOAD!
  2. CaptOz

    CaptOz Member

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    Ok.. thanks..

    I have old school Teleflex throttle and both have been checked for max Governor travel. Infact, Throttle position of 5/8th travel puts governor at max position currently.
  3. Capt J

    Capt J Senior Member

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    I don't know how you're getting that info. I really think your actual weight measurement is really off that you're plugging into the Formula. Generally cutting 1" of pitch gets you 50 rpms on a 2300RPM diesel like the Detroits. You were at 2250 with 29x33's and should have had 29x32's. The boat is light by about 10,000 lbs of fuel,water and interior and only making 2000 rpms. So really should shoot for 400 rpms, figuring in all of the weight you are adding. Try Lauderdale Propellor as they may have some used ones. What size did Frank and Jimmy's recommend?
  4. CaptOz

    CaptOz Member

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    Im using 82500 lbs for a loaded vessel. I understand your 50 rpm per inch of pitch though, however the Boatdiesel.com propeller calculations yield 29 x 31. I would love to test 29 x 31 all the way down to 29 x 27 and compare sea trial results. I have an account at LP I will see if they have any loaners. I also have a 4 bladed set in the lazarette 29 x 29 that is probably less loading than my 29 x 33's. Btw they also have a medium cup.

    Im hauling out on Friday for routine bottom work so I will have a fresh bottom soon.

    Thanks for the input Capt. J.
  5. Capt J

    Capt J Senior Member

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    Try the 4 blades!!!!!!!!!. 29x29" 4 blades are closer to what you're looking for and probably equivalent to 29x30" 3 blades. But a good prop shop can calculate what you need, based upon numbers you get with the 4 blades.
  6. CaptOz

    CaptOz Member

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    Will do! Thanks..
  7. CaptOz

    CaptOz Member

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    Here are the new numbers with my 4 bladed 29 x 29 medium cup.

    WOT 2265rpm
    Boost: 20 PSI Stbd, 18 PSI Port
    Fuel Consumption: 42 gph each
    Speed: 25 Knots

    As expect we gained some more RPM with less pitch. About 200 more. However boat still very light. Im hauling her out Friday to paint bottom, prop speed,etc etc.

    Boost seems a little low. But then again RPMS are not there yet.

    Also, I noticed something funny with Starboard throttling. It doesnt seem to hold around 1850 RPMS. When I try to drop it to 1850 from 2000 it goes down to 1700. Then if if I try to just tap it to match other engine it shoots right back up 2000. GPH goes from 22 to 30 but I cant seem to match Port which is steady at 24. I will have my mechanic check it out.

    I am sending both Flowscan meters back to reset the hours and I will have them check everything. Also will recal tachs when they get back to match engine.

    Making some progress, but not there yet.
  8. Capt J

    Capt J Senior Member

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    Something sounds like the governor in the stbd engine might be hanging up or binding at that rpm point.

    You're getting closer on RPMs, 29x29 3 blades would put you right where you need to be at current weight but then when the normal weight is added you'll end up needing 29x28's 3 blades. I think your boat is probably better off if you stick to 4 blades and repitch them. At this time I would wait until all the interior and fuel and water are filled and see what that does to rpm's with the 4 blades on and seatrial then. Also, buy a photo tach and read RPMs from the engine balancer, your tachs could be off 100-200 rpms too. What speed are you getting at 1900? Last 54' Bertram I ran had just a hardtop and relatively fresh 12v92's and only cruised at 22-23 knots at 1900 with the cockpit fuel tank empty and no owner gear.
  9. CaptOz

    CaptOz Member

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    Capt J.
    Thats exactly what I am going to do. Once Im out of the Yard I will load her back up and will see where she is at.

    Frank and Jimmie's prop Calculator for my boat, hp, weight, etc , yielded:

    29 x 31 for 3 blades
    29 x 29 for 4 blades

    If I can cruise at 22knots(1900-1950) with a little more than half the load I am happy.
  10. Capt Ralph

    Capt Ralph Senior Member

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    10 psi fuel pressure or 10psi boost pressure?
  11. Capt Ralph

    Capt Ralph Senior Member

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    I tried to express that and check full tube / rack travel.
  12. CaptOz

    CaptOz Member

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    rcrapps:

    That post of 10 psi was Turbo Boost, but I was taping into the wrong port . I am now seeing 20PSI at WOT of 2265RPM.

    Fuel Pressure was measured at 60 psi.
  13. Capt Ralph

    Capt Ralph Senior Member

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    Those are good numbers.