Click for JetForums Click for Cheoy Lee Click for Walker Click for Lurssen Click for Burger

Repowering a 54' Donzi Sportfish

Discussion in 'Donzi/Roscioli Yacht' started by DOCKMASTER, Sep 5, 2019.

You need to be registered and signed in to view this content.
  1. DOCKMASTER

    DOCKMASTER Member

    Joined:
    Feb 26, 2012
    Messages:
    285
    Location:
    Ketchikan, Alaska
    Thank you PacBlue that is really helpful. Now I just need to better understand what the safety factor really means? In other words, I realize the 5.0 factor is preferred? But if I'm at 4.68 now and never had any issues, how much risk am I taking by dropping down to say 3.56 factor? I don't back hard chasing marlin or have any need to accelerate quickly. I also bring things up to cruise slow and steady. Does that change anything or is the safety factor needed more during cruise, heavy seas and WOT? Maybe the greatest shaft stress is in/out of swells and heavy chop?
  2. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,557
    Location:
    Dana Point, Ca
    Here is the shaft calculation from the Western Branch Metals catalog: http://www.wbmetals.com/

    upload_2019-9-9_13-20-12.png

    As far as the Safety Factor goes, ABYC recommends 5.0 for ALL Diesel installations. It has been my experience if you go below 5.0 even to 4.0, you will experience premature shaft failure/breakage. If I had to design and be responsible for shafting, I would not go below 5.0 , even though you have been ok at 4.68. I could not recommend a sf below 4.0. The SF of 2.0 is for a gas engine installation, fyi.

    upload_2019-9-9_13-23-20.png
  3. Jorge Lang

    Jorge Lang Senior Member

    Joined:
    Nov 17, 2003
    Messages:
    286
    Location:
    Fort Lauderdale
    If you haven't plan on the exhaust yet, I know a guy;).
  4. DOCKMASTER

    DOCKMASTER Member

    Joined:
    Feb 26, 2012
    Messages:
    285
    Location:
    Ketchikan, Alaska
    I'm supposed to hear back today from ZF on available ratios and lead times. If I do need to change shaft size then it makes sense to go with the 1.97:1 ratio. Any idea what the AQ22 material runs in the 2.75" - 3" diameter? I assume it is sold by the foot?

    On the subject of gear ratios; any speculation as to whether I would see a noticeable performance or efficiency difference in the 1.525:1 - 1.97:1 ratios being considered?
  5. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,557
    Location:
    Dana Point, Ca
    All the above numbers are based on AQ 22 HS (High Strength), not the lesser strength normal AQ 22.

    AQ 22 HS has a yield strength in torsion of 70,000 psi for shaft diameters from 2-1/4" to 6". See the last column
    Regular AQ 22 is at 63,000 psi up to 2-1/2", then drops to 50,000psi from 2-1/2" too 3", requiring an even larger shaft diameter.

    For AQ 22:
    upload_2019-9-9_15-57-58.png

    I have no idea of the cost, contact them to see who is the distributor in your area.
  6. Donzi 54

    Donzi 54 Member

    Joined:
    Oct 21, 2009
    Messages:
    88
    Location:
    Point Pleasant, NJ & Morehead City, NC
    My struts where replaced, don't know if it was possible to bore them. The shaft logs were able to be bored out to except the larger forward shaft bearings
  7. DOCKMASTER

    DOCKMASTER Member

    Joined:
    Feb 26, 2012
    Messages:
    285
    Location:
    Ketchikan, Alaska
    Sorry Lew, I misunderstood a post from a few years ago.
  8. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,557
    Location:
    Dana Point, Ca
    More food for thought.

    Keep in mind that there is a relationship between shaft diameter and other key geometry items in the propulsion system.

    A selected Shaft Diameter has a specific Taper Length, and this needs to be checked with the propeller hub length when changing shaft diameter. If unchecked, and the propeller hub is a bit short in length for the larger shaft diameter, you will have a larger gap between the forward face of the propeller hub and the aft face of the strut barrel. You want this dimension to be around 1/2 of the shaft diameter, no greater than 1 x the shaft diameter.

    SAE Propeller Shaft Geometry:

    upload_2019-9-10_10-46-54.png

    Cutlass bearings have a geometric relationship with shaft diameter as well. The length of a cutlass bearing is usually 4 x the shaft diameter, so a cutlass bearing for a 2-1/2" shaft is 10" long while a cutlass bearing length for a 2-3/4" shaft is 11" long and for a 3" shaft is 12" long. The strut barrel may or may not be able to take a standard length cutlass bearing, as it can be just enough to accept a 10" cutlass bearing, so you may have to machine an non-standard bearing length for a larger shaft diameter if this is the case. Get the tape measure on this. Their OD varies as well. For a 2-1/2" Shaft, a Cutlass Bearing can have an OD from 3-1/8" to 3-1/2" depending on make and model, a 2-3/4" Cutlass Bearing is 3-3/8" to 3-3/4" OD and a 3" Cutlass Bearing is typically 3-3/4" to 4" OD.

    Cutlass bearings:

    http://www.duramaxmarine.com/pdf/CutlessBearingMS.pdf
  9. DOCKMASTER

    DOCKMASTER Member

    Joined:
    Feb 26, 2012
    Messages:
    285
    Location:
    Ketchikan, Alaska
    We will look at all this once the boat is out of the water and in the building. That's scheduled for late this month. Right now I'm leaning heavily toward going with the 1.97:1 ratio and upsizing the shafts and getting new props. I won't be able to determine what shaft size is reasonably possible (2.75" or 3") until we have more info when out of the water.
  10. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,557
    Location:
    Dana Point, Ca
    The best case is to use the existing strut with a larger cutlass bearing. I believe the Donzi 54 repower went up in hp significantly so the strut up-grade makes engineering sense in that case with the increase in power and speed. Your remaining in the same ball park, hopefully it works out for you after you inspect it at haul out.

    From a design and engineering standpoint, the 1.971/1 gear ratio is desirable for the following reasons:
    1. Reduces the propeller tips speeds, they are too high at 1.6/1 IMO.
    2. Reduces the design cavitation number
    3. Allows for a better propeller design selection - better blade loading
    4. Should be smoother
    5. Should be quieter/less cavitation
    6. Should have an efficiency advantage at cruise, on both speed and fuel consumption
    9. Will give you a little more "bite" during docking/maneuvering
  11. Donzi 54

    Donzi 54 Member

    Joined:
    Oct 21, 2009
    Messages:
    88
    Location:
    Point Pleasant, NJ & Morehead City, NC
    PacBlue, that is some great info. Now I find myself rechecking that everything was done the way it should have been.
  12. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,557
    Location:
    Dana Point, Ca
    While you are currently in discussion with ZF, I would take it one step further and ask them what would be the optimum gear ratio for your repower? It wouldn't hurt and it would give you another engineering point to consider. They would have to have the usual existing performance data, weight, and current propeller.

    Donzi most likely selected the original 1.6/1 ratio to keep builder costs down with a 2-1/2" shaft system. A 2-3/4" shaft is fine, maybe a little unusual to source, and a 3" shaft system would have been even more builder's cost. I am sure they did not sit down with their supplies to create an optimum system, surprising as it may sound.

    Your trade-offs for this repower would then include:

    1. Standard 2-1/2" System with a less than optimum 1.6/1 ratio.
    2. A modified 2-3/4" Shaft System with an upgraded 1.971/1 ratio.
    3. Open question to ZF - what is the optimum gear ratio and propeller match for my repower. This may in turn validate item #2 or give you something else to consider based on your repower budget, project timeline and the ZF response.
  13. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    11,330
    Location:
    Fort Lauderdale
    Quite honestly, I'd call Bob Roscioli himself at Roscioli and ask his opinion. He knows these boats inside and out and knows what works with them and doesn't, he built them.
  14. DOCKMASTER

    DOCKMASTER Member

    Joined:
    Feb 26, 2012
    Messages:
    285
    Location:
    Ketchikan, Alaska
    All the furniture, cabinets, TV lift, carpet, etc have now been removed from the salon. Upon removal of the A/C valance in the ovhd of the salon we found some ugly rot behind there. Obviously this will have to be repaired. IMG_3318.JPG IMG_3319.JPG IMG_3320.JPG IMG_3321.JPG
  15. DOCKMASTER

    DOCKMASTER Member

    Joined:
    Feb 26, 2012
    Messages:
    285
    Location:
    Ketchikan, Alaska
    So I finalized some decisions and have all the big stuff now firmly on order:

    2(ea) CAT C-18 ACERT @ 1150 mhp -
    2(ea) ZF665A gears with 1.97:1 ration, 10 degree down angle, electronic trolling valves and AMOT thermostatic valves (we are in cold water and required to keep oil at temp).
    ZF Smart Command propulsion controls with back-up processor and back-up control panel
    Deangelo Marine Wet exhaust for the C-18s
    1(ea) Northern Lights 20kw gen with Gem series sound enclosure, secondary isolation mounts and remote digital panel
    1(ea) Northern Lights 9kw gen with Gem series sound enclosure, secondary isolation mounts and remote digital panel
    Reverso GP-806 heavy duty 6 valve oil change system

    Still to sort out and order:

    - hydraulic pump for power steering. Options are electric or PTO driven off gear. I'm researching electric and prefer if I can't find solution
    - Determine shaft size of 2.75" or 3" and order AQ22HS shafts
    - get more prop recommendations and order
    - haven't decided on watermaker yet. I may just rip out the old from the engine room and install new later. I have never used it but would like to have one in case needed.

    Yes, there are numerous other small items. I'm just covering the bigger stuff initially. I likely won't have much to update for a few weeks until after we get out of the water and really get going in earnest.
  16. wiredup

    wiredup New Member

    Joined:
    Jul 20, 2016
    Messages:
    25
    Location:
    va beach
    Great project!! Maybe I missed it, why are you adding only a 9kw backup generator, and not a 2nd 20kw?
  17. DOCKMASTER

    DOCKMASTER Member

    Joined:
    Feb 26, 2012
    Messages:
    285
    Location:
    Ketchikan, Alaska
    The 9kw is not a back-up. The boat originally had a single 20kw. However, 95% + of the time, the 20 kw is way overkill. So the 9kw will be used for 95 % of the time and meets the load demand. The 20kw only used for high load conditions. So in essence, the 20kw is more of a back-up then the 9kw. Besides, I don't have enough room for another
    20 kw even I wanted it.
  18. DOCKMASTER

    DOCKMASTER Member

    Joined:
    Feb 26, 2012
    Messages:
    285
    Location:
    Ketchikan, Alaska
    Curious if folks have recommendations on where to list the stuff coming out for sale? Engines, gears, full DDEC system, etc. Looks like Ebay is used quite a bit. Any other sites or places recommended? Are there any companies out there that will come but everything in a lot?
  19. Donzi 54

    Donzi 54 Member

    Joined:
    Oct 21, 2009
    Messages:
    88
    Location:
    Point Pleasant, NJ & Morehead City, NC
  20. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,557
    Location:
    Dana Point, Ca

Share This Page