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Buying 54' Donzi

Discussion in 'Donzi/Roscioli Yacht' started by DOCKMASTER, Feb 26, 2012.

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  1. AlfredZ

    AlfredZ Senior Member

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    Hi there,

    First of all, best of luck on your new purchase.

    Regarding the gap between the struts and props, I have heard that many many times that it should not acceed twice the diameter of the shaft and it is better when it is the same diameter, apparently because then it will cause vibration and loss of speed. By practical experience, I never had ANY boat that was less than twice and never had problems with vibration (needing to change any part before its expected time) or loss of speed. The only thing I can agree with is that if you are looking for pushing hard on the throttles to juice more speed fast then you might effect the parts but after all this is a sport fisher so even under tournament conditions it won't be pushed as ruff as sports or speed boats are pushed, specially that you will not be trolling in slaloms at 30knts!

    Again, good luck and happy fishing.

    Cheers!
  2. DOCKMASTER

    DOCKMASTER Member

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    Thanks for the input. My only concern here is my last boat (39' Sportfish) had a shaft break right at the start of the taper. What a pain running back in on one engine and then replacing a shaft and props. That was an expensive day I'll not soon forget. I just want to be sure what is on the Donzi is suppose to be that way from the factory. If it has lasted 18 years then I don't see a problem.
  3. AlfredZ

    AlfredZ Senior Member

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    Good point, I will consult a friend, (a boat techy), and even see if a blueprint is available to check the angels and dimensions.

    Cheers.
  4. Kafue

    Kafue Senior Member

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    Engine survey

    This may be stating the obvious as you may already be doing far more than the oil analysis on the engines, but just in case:
    When I purchased my Hatteras with fullly over hauled 12V71N's, I asked for a full engine survey and was very impressed with the surveyors work.
    He used a fibrescope to inspect the cylinders in the air boxes, checking to see that there was not too much scuffing by viewing the cross hatching. The oil analysis was also done, however it doesn't really tell you too much unless there has been a serious issue or if the oil was recently changed.
    Worth the extra dollars for peace of mind.
  5. Donzi 54

    Donzi 54 Member

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    I can tell you for sure that mine are differently not that much. Doesn't that boat have 3" shafts?
  6. DOCKMASTER

    DOCKMASTER Member

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    I haven't measured the shaft diameter but according to the survey they are 2.5"
  7. Bamboo

    Bamboo Senior Member

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    Somehow it seems strange that there are 2.5"s there- I have the 16-92's in a 65 and have 4 inch shafts and B Roscioli "overbuilt" his boats. At 1450 HP I don't need any more than the 3 inch shafts. Even 3.5 would be more than enough- which leads me to believe you have 3 inch shafts.

    On the shaft overhang I just had my shafts shortened last year. I also had shorter prop hub than I was supposed to have. Mine were 5 inches on one side and just over 6 on the other. The previous captain ran aground and the shafts were changed (I think) and the rudders were (I know). The shortening did cut down on the cruising vibration. I also have the Japanese twin disc copies for gears which have a 2/1 ratio- that itself make vibration at 2/1. Do you have Federal props? You may have those with a shorter prop hub and could buy props with a larger hub to cure any issue you have instead of cutting the shafts down.

    In any event I would worry more about vibration than a shaft breaking at the taper.
  8. DOCKMASTER

    DOCKMASTER Member

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    Thanks Bamboo. No idea what brand of props are there. Survey says they are 28x37 NiBral. I'll measure the shaft diameter when I trial the boat on Friday. I'll also pay attention to any vibration issues.
    The gears are Detriot 272 A with a 1.6:1 ratio. I think these were made by Allison for DD.
  9. DOCKMASTER

    DOCKMASTER Member

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    According to the shaft calculator on boatdiesel.com even if they are 2.5" shafts they would still easily handle the 1150 hp of the 12v92's. And I don't know what grade of Aquamet they are so that was using the weakest one listed and a safety factor of 2. Further I don't have any intention of running this boat hard or at WOT (much) :)
  10. Capt J

    Capt J Senior Member

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    Except 12v92's after the first 200 hours are more like 950hp...... Every boat I've ever run with 12v92's seemed to have lost 200hp somewhere after the first 200 hours and had to have the props cut.....from then on out they stayed the same, even after majors they stayed the same......
  11. Donzi 54

    Donzi 54 Member

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    You should have 3" shafts in that model. Mine came with 3" and don't see any reason why Roscioli would have changed.

    Take a hard look at the rudders on that boat mine had to be replaced with stronger models made by Western Branch Metals. The original ones where made very thin, knife like and had issues with vertical cracks near the rudder stock. But that said they where not designed to run at the speed my boat is now capable of doing. And I never noticed the cracks till a year or two after the re-power. I know Roscioli redesigned them but I don't know if that was done on the 54's or not.
  12. DOCKMASTER

    DOCKMASTER Member

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    I seatrialed the boat Friday and everything went well so I'm moving ahead with the purchase. The boat ran and handled well. Cruised at 24-25 knots at 78% load and easily came up to full RPM and ran about 31 knots WOT. These numbers were with close to full Fuel and water.
    The shafts in this boat are definitely 2.5". No idea why they wold be different than some of the other 54's out there but it is.
    The boat definitely needs some TLC and I'll start getting systems serviced and back on line immediately. i received an acceptable credit from the seller to deal with deferred maintenance so overall I'm very satisfied with the deal
    I was particularly impressed with how the boat turned both at higher speeds and at idle. Cruising thru the harbor in low idle with only one engine in gear and the steering still responds quite well. It only takes about 7-8 degrees of rudder to steer straight with one side in gear.
    Thanks for everyone's input. It really helped. I'm sure I'll be back on here soon to ask a lot of questions. The seller I have dealt with knows little about the boat so I'm left to figure out most of the systems myself. At least I was ale to get all the original manuals and info so that will help tremendously.
  13. SHAZAM

    SHAZAM Senior Member

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    That seems very un-donzi like.
  14. AlfredZ

    AlfredZ Senior Member

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    Congrats are in order then, best of luck with it.

    Cheers.
  15. DOCKMASTER

    DOCKMASTER Member

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    I hear you but can't see it as a reason to not buy the boat. Does any disagree? It's not like at 2.5" the shafts are considered undersized by any means.
  16. Capt J

    Capt J Senior Member

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    No, if the shafts are properly sized for the horsepower, then I don't see any reason that would be a deterrant.
  17. Donzi 54

    Donzi 54 Member

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    Looking back though an original brochure it says that the 2.5" shaft was standard with the 12v92 engines.

    Good luck with your purchase
  18. SHAZAM

    SHAZAM Senior Member

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    I own a 65' Donzi and just finished up rebuilding the entire machinery space. Based on my experience with my Donzi as well as others that I'm familiar with, I thought 2.5" seemed a bit undersized. Regardless, congrats on the purchase.
  19. Capt J

    Capt J Senior Member

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    It all depends. The smaller the shaft, the less drag and theoretically more speed. I worked on a 75' Jim Smith with 2000hp 16v2000's that had 2 1/2" shafts, but they were a special shaft that was splined like an outboard and didn't have a keyway, making it stronger for it's diameter.
  20. DOCKMASTER

    DOCKMASTER Member

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    Where can I find the brochure you mention? Is it online? That would be interesting reading.

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