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54' Bertram Speed, Specs, Prop Size

Discussion in 'Bertram Yacht' started by CaptOz, Apr 13, 2009.

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  1. CaptOz, Apr 13, 2009
    #1
    CaptOz

    CaptOz Member

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    Location:
    Miami, Fl
    Hi,

    I recently bought my '86 54' Bert and have since installed flowscan device. The boat has the 900HP DD 12V71s marinezed by Key Power out of Miami, FL(They are no longer around).

    I am not running original props. So my first question is does anyone know the original size of props for this boat with this hp setup? I am currently running 4bladed wheels, not sure of the exact diameter or pitch. There is a spare in the lazareth that are 3 bladed. I would love to know what the original size was.

    Next question is what should be the cruising speed and top speed on this boat? I am seeing about 20Knots at 1900 RPM and 24knots at 2250RPM(WOT). Supposedly the injectors have been de-tuned to 870HP ones.
    I am burning 75 gallons an hour at cruise, but have not done the final cal on the flow scans yet. When I look at the fuel consumption curve for this engine it says that at 1900rpm gph should be around 28 gallons per hour per enigne. Why should I be seeing such a big differnce? Also, my trim tabs have been modified to be stuck in the down position. I read that this actually make the boat 2 to 3 knots faster, but does it come at a cost of higher GPH?

    Thanks in Advance,
    CaptOz
  2. NYCAP123, Apr 13, 2009
    #2
    NYCAP123

    NYCAP123 Senior Member

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    I never heard of diabling the trim tabs in the down or any other position and would assume that it would have to affect gph. I just pulled this off an ad on the net. Check those speeds.
    I juClass:power
    Category:Convertible
    Year:1986
    Make:Bertram
    Model:54 Convertible
    Length:54
    Location:Rockport, TX
    LOA:54
    Beam:16'11
    Engine Model:12V71TI
    Horsepower:900
    Cruising Speed:27
    Max Speed:34
    Propulsion Type:TWIN
    Hull Material:FIBERGLASS/COMPOSITE
    Fuel Type:DIESEL
    Fuel:1200
    Water:250
  3. Capt J, Apr 13, 2009
    #3
    Capt J

    Capt J Senior Member

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    Location:
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    I am not sure what propellors your Bertram came with. However 12v71's should turn 2300rpms at WOT and you're a tad overpropped but not enough to worry about in my opinion.

    It does sound like you have smaller injectors in your 12v71's. Every set of 12v71's I ran burned 90 GPH at 1900-1950rpms. I ran one 54' Bertram with 12v71's, it only had a hardtop and I remember it running 29 knots at 1950 rpms, this was with 4700hrs without rebuilds and they were very worn according to the engine surveyor to the point he did not want to do a WOT on them.

    Sportfishes do generally gain a few knots with the trim tabs down. They also usually run fastest when you drain fuel from the front and keep the aft tank full and tabs down. However the only sportfish I know that had trim tabs in a fixed position were Strikers. I would prefer to have the trim tabs operational and have the ability to trim them where you want them for sea conditions. I wouldn't want the trim tabs full down in a following sea for example.
  4. CaptOz, Apr 13, 2009
    #4
    CaptOz

    CaptOz Member

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    Location:
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    Thanks.. Yes 2300 is the spec but with smaller injectors maybe 2250 is ok. I do get some trail of grey smoke and my transom gets soot after long runs which probably means I am over prop's as you suggested.

    I was wondering if I could cut the GPH some how from 75~80 to about 60ish, but from what you are telling me.. I should be happy and quit wining!

    .26 is the best KnMPG is see and thats around 1800.

    -CaptOz
  5. Capt J, Apr 13, 2009
    #5
    Capt J

    Capt J Senior Member

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    I highly doubt you can cut your GPH anymore. What you can do is run at hull speed. Your engines with those injectors should burn about 10gph at 1000 rpms and you should be close to 10 knots at that speed. The 12v71's are very very economical running at 1,000 rpms or less. I run a few yachts that way for 4-6hrs, then run them at 1950 for 1/2 an hour to clean out the airboxes and then back down to 1,000rpms. I ran a 75' MY on a 5300NM trip that way and averaged 1.6 gpm and that was with the generators running twice as many hours as the engines. I don't know if you can stand to run at that speed.......it should be a good speed to troll lures at, if you're at 1,000 rpms......
  6. CaptOz, Apr 13, 2009
    #6
    CaptOz

    CaptOz Member

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    Location:
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    Capt J,

    Thanks for the input, I will see what my KnMPG is at 10knots.. hopefully 1.0! I did see 1.46 KnMPG trolling at 675 rpms this past weekend and doing 7 knts.

    Do you think 3 bladed props will give me better economy? I know it will take longer to get out of the hole, but top speed increases usually. Also, do you think the trim tabs on that boat are too small? I spoke with Bennet Marine and they recommeded 48" x 9" if length allows. Current size is around 32" right now.

    -CaptOz