Click for Alexseal Click for Burger Click for ZF Click for Walker Click for Lurssen

Considering Repowering Again

Discussion in 'Technical Discussion' started by DOCKMASTER, Jul 24, 2019.

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

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    7,386
    Location:
    Satsuma, FL
    We live and cruise on a 41 year old Bertram. Still 32Vdc and 12V71TIs. Tied next door, 30 year old 12V71TAs.
    I believe in stocking spares. If I don't have it, tomorrow morning I will for either boat.

    Probably the hardest to find items on your engines is the exhaust manifolds. Shop, get them and pickle them.
    IMO, al else is still serviceable.

    You did comment also short on old Detroit techs your way.
    I do understand that and this must be considered.
    If your like me, Your hands have already been into it, we just need some young strong backs.
  2. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,565
    Location:
    Dana Point, Ca
    It’s important to keep in mind that repowering an old DD with a modern diesel will give you a rejuvenated boat. In this case, lighter, faster more fuel efficient and more engine information underway. And hopefully quieter. That is the real best case or upside, you will have a better product and you get the satisfaction of a refit well done.

    Modern props will go a long ways towards making a better quality of ride , less vibration and more responsive Plan on replacing your shafts , cutlass bearings and maybe shaft seals at the same time.

    In a previous thread on YF you had 2-1/2” shafts, because of the old school 1.6/1 gear ratio. You may have to go from a 4 blade to 5 blade prop with the new engine choice, but all that can be calculated and optimized prior to starting the project.
  3. DOCKMASTER

    DOCKMASTER Member

    Joined:
    Feb 26, 2012
    Messages:
    285
    Location:
    Ketchikan, Alaska
    All great info any very much appreciated. I wasn't planning on replacing shafts unless a problem is found. We pulled shafts a few years back and did a complete NDT inspection and all was good. Replaced cutlass bearings at same time. They are easy enough if new is required. I will explore the props to see what is needed there. I believe my existing gear ratio is 1.97/1 and I was thinking to replace with same if available.
  4. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,565
    Location:
    Dana Point, Ca
    1.97/1 is definitely a better situation for 1150 hp and 2300rpms. Sounds like you should be good on shafts, already saving money :)
  5. DOCKMASTER

    DOCKMASTER Member

    Joined:
    Feb 26, 2012
    Messages:
    285
    Location:
    Ketchikan, Alaska
    I met with CAT dealer late last week. Will see what kind of proposal they come back with. They are also going to give me some detailed drawings of engines w/gears so I can really see how the C-18s or C-32s would fit.

    On a side note, for the C-32 option I wonder if my air intakes would be too small? I can't even imagine how you would address that issue. Same with exhaust. I think my pipes are 10 or 12 inch each side as they exit the boat. If either or both of those had to be upsized I think that would put me out for sure on the 32s
  6. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,565
    Location:
    Dana Point, Ca
    My rules for a repower - First , reduce weight and gain a bit more horsepower, as your cruise speed will definitely increase and you will get better fuel economy. Second - get new propos, as there have been gains in prop design resulting in better performance since your boat was built - Veem or Michigan Wheel.

    Check your gear ratio - I looked back in the Donzi archives and when you bought the boat you stated "The gears are Detriot 272 A with a 1.6:1 ratio. I think these were made by Allison for DD." This would explain the 2,5" Shaft diameter because a 1.97/1 ratio would require at least a 2-3/4" Shaft for the 12V-92TA's. Check it out again to make sure.

    The 2.5" Shafts do not have the right Safety Factor for the CAT C-18's rated at 1150hp if you are using a 2.0/1 gear ratio, even with AQ 22 High-Strength Shaft material. For recreational Diesel boats you need at least a calculated safety factor of 5.0. You would have to go to a minimum of 2-3/4 Shaft, AQ 22 HS. But keep in mind that a 2.0/1 gear ratio gives you a better prop, i.e., less potential cavitation as it slows it down a bit. Ideally, you would design the propulsion system around a perfect gear ratio, a compromise of space available due to shaft angle and a low incidence of predicted cavitation. This is what gives you the best cruise at the smoothest levels of vibration. A CAT C-32 definitely requires 3.0" shafts, assuming you are going with a rating in the 1450 - 1600 hp range.

    The air intakes for a C-18 should be fine in your cooler Alaskan climate. Higher power C-32's would have to be calculated and may (would) require a change. The C-32's are just too much weight in my opinion, and the MTU 10V2000 would be a better choice if higher speeds are your goal.

    C-18's and a SeaKeeper, if you don't already have one, look like the best bang for the buck IMO.
  7. DOCKMASTER

    DOCKMASTER Member

    Joined:
    Feb 26, 2012
    Messages:
    285
    Location:
    Ketchikan, Alaska
    You are correct and I was mistaken on gear ratio. The existing gears are 1.6:1. The gears are badged Detriot then have a Twin Disc model number. They were made for Twin Disc by a Japanese company (can't recall the name). We unraveled all of this when we rebuilt the Stbd gear a few years ago after a failed cooler put sea water into the gear.

    Hopefully I can stay with existing 2.5" shafts. Really don't need a SeaKeeper as most of the time we are in the Inside Passage and protected waters.
  8. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,565
    Location:
    Dana Point, Ca
    If you are keeping the Shafts at 2.5" Diameter, then you will have to remain in the 1100hp / 2300 rpm / 1.6:1 Gear Ratio range. Twin Disc had some gear models supplied by Niigata, a Japanese company. Will have to assume the shaft material is AQ 22 High strength.

    This would eliminate the C-32, so the focus would be on a C-18 which gives you a better weight savings anyways, especially if you have no need for the SeaKeeper.

    So the next focus would be on propeller selection, as 1.6/1 ratio is fairly challenging, your blade tip speeds are typically considered high, you'll have to watch cavitation inception and should start that discussion with the propeller suppliers in your area. You can manage some of it by going to a 5-Blade design, Veem or Michigan Wheel. They can provide the calcs, especially if you have a ballpark weight estimate to go with your current cruise/wot speeds.
  9. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    11,343
    Location:
    Fort Lauderdale
    I would stick with C18's as you'll see about 3 knots more speed than the Detroits at 86 GPH @ 80% load for both. The C32's, aside from being much physically larger and much heavier will be fuel hogs in the boat, 1600 HP C32's will burn about 125 GPH @ 80% (both) and probably only another 4 knots of speed over C 18's, plus the expense of new shafts/struts/ etc.

    I wouldn't touch Michigan Wheels in a SF, they are poor technology in comparison to Veems and with this gear ratio you will absolutely get prop burn with the shaft speeds With Michigans. Veems would be my choice. You can also go with a splined shaft/prop (instead of keyways) and that will also increase your safety margin on the same size shaft, if you're replacing shafts. Most custom SF run splined shafts/props and thinner shafts to increase speed/efficiency. Also I wouldn't be in such a hurry to switch to 5 blades either, unless you need the stern lift, as you'll get more speed with 4 blades. I just ran a 62' MY with 1200 mans, and 4 blade Veems and I believe it had 2" shafts and around a 2.0:1 gear ratio, cruised at 26 knots +/-.

    If a 1.6:1 gear ratio has worked fine in the boat, the boat will be faster than going to a 2:1 gear ratio. The faster you spin a prop, (lowest reduction gear you can get away with) the faster the boat runs usually (speed) as you get a little more lift. I worked on a 2003, 75' Custom SF, full tuna tower, twin 2000 HP engines, 2.5" shafts, 1.5:1 reduction gear, 4 blade props, and it cruised 35 knots, topped out at 43 knots. It performed perfectly. At 1200 rpms the boat was fully on plane and did 20 knots.
    Last edited: Jul 31, 2019
  10. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,565
    Location:
    Dana Point, Ca
    I have tested and used pretty much all of the current prop manufacturers out there. I really like Veem for their manufacturing quality and quietness underway, when you receive them fresh from the factory they are like a piece of jewelry, absolutely flawless.. With that being said, the Michigan Wheel M-500 props are as technically sound as the Veem's. They have been designed by one of the leading hydrodynamic experts in the country and are a bit more affordable than the Veem's. All propellers have experienced burn at some time or another, the successful ones manage it better than the others. The Hatteras GT 60 had a problem and went back and forth between Veem and MW and ended up with MW I believe. Viking has partnered with Veem and has remained steady with them.

    Splined shafts do not reduce the shaft diameter or increase the safety factor, as the shaft size are calculated with Torsional Strength as the main material criteria. The gear ratio drives the shaft diameter for a given horsepower and the Torsional Strength of the shaft material, and the old school 1.5 (1.6) /1 ratios are not seen as often now as the hp increases have put further demand on the propellers. What we have seen is an increase in Propeller blade area, number of blades, and better blade design, especially at the blade root/intersection of the propeller hub. Not all burn issues are attributed solely to propellers, as the strut design, hull strakes and thru-hulls can be problematic if they affect the inflow to the propeller in a adverse way.

    Comparing custom SF or MY's data is an Apples v Oranges conversation. You can easily look at production SF models and you would be hard pressed to find an old school 1.5/1 gear ratio amongst them, look at the Hatt 59, Viking 58, Bertram 61. With the weight of a production boats and the higher hp on new engines, you wont see these gear ratios. The fastest production SF boats today all have gear ratio's over 2.0/1. Comparing prop speed on gear ratio alone completely ignores efficiency/slip/cavitation/vibration, all the stuff that really matters when engineering a correct propulsion system.
  11. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,565
    Location:
    Dana Point, Ca
  12. DOCKMASTER

    DOCKMASTER Member

    Joined:
    Feb 26, 2012
    Messages:
    285
    Location:
    Ketchikan, Alaska
    I met with CAT last week. They are working up a proposal. More when I get something..........
  13. DOCKMASTER

    DOCKMASTER Member

    Joined:
    Feb 26, 2012
    Messages:
    285
    Location:
    Ketchikan, Alaska
    So I have decided to move forward with the repower project. I'm finalizing some details with CAT but I'm going with the C-18's at 1150 hp (1136 bhp). I'm still trying to decide which gears to use. I've been quoted the ZF 550-1A which is rated for 1207 bhp for up to 500 hrs/year. I will likely never see near 500 hrs years. However, I'm still considering the ZF 665 which has a higher duty rating. I'm still awaiting some details from ZF and have asked some questions if the 550 model will support the long hours of trolling we sometimes do.
    I'm also planning to go with the ZF Cruise Command Control System with the MC 2000-2 all chrome control heads.
    Does anyone have real world feedback on the ZF 550 or 665 gears? We have built some commercial boats that use the 665 behind the C-18 and they are pretty bulletproof. Just wondering if this will be overkill for my application.
    Also wondering if I should keep my existing emergency manual back-up controls with the Cruise Command controls? Anyone experience failures with these controls?

    I'm going to replace both of my gens at the same time and likely go with Northern Lights

    I will start another thread and include pictures once we get started on the project.
  14. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,565
    Location:
    Dana Point, Ca
    Great, looking forward to the repower. Have you settle on a gear ratio yet?
  15. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    11,343
    Location:
    Fort Lauderdale
    Yes, but their metallurgy isn't anywhere near Veems, and they don't perform as good as Veems.
  16. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,565
    Location:
    Dana Point, Ca
    True on the metallurgy, Veem uses a higher amount of virgin copper than others due to being near the source in Australia.

    Not so true on performance, just keep tabs on the top dog sf, , not necessarily the production guys.
  17. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    11,343
    Location:
    Fort Lauderdale
    I've used both on several brand new SF over the years, on the same boats with both propellors, the Veems aside from having less vibration, were around 1 knot faster. On one boat the builder had to take one set of Michigans off at 48 hours because they were so prop burned it looks like they'd fling a blade and put Veems on it and all was well in the world. On high HP fast SF, the Michigans will flex.
  18. DOCKMASTER

    DOCKMASTER Member

    Joined:
    Feb 26, 2012
    Messages:
    285
    Location:
    Ketchikan, Alaska
    I'm going with the ZF 665-A with 1.525:1 ratio. This is the closest ratio I can get to my current 1.6:1. I'm told at WOT at 2300 rpm the shaft will have about 100 rpm more than my current ratio. I haven't decided yet if I will get new props or not or try to use my existing ones.

    I was originally quoted ZF 550 gears but the 665 is rated at 2500 hrs/year vs 500/year for the 550 gears. Given I'm in a bit of a remote area and once the gears go in they can't be removed from the engine room I wanted the more robust gears.
  19. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,565
    Location:
    Dana Point, Ca
    That’s a smart upgrade to go with the 665 gear, nice to have the peace of mind for the better duty cycle. The 1,525 gear ratio will keep the 2.5” shafts in good shape with a safety factor over 5.

    You can take the original prop and get them cleaned up and reconditioned to use as a test prop on sea trials and gather the performance data. Investing in the repower, it makes sense to finish it off with a new prop once you know the numbers.
  20. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    7,386
    Location:
    Satsuma, FL
    A+
    A+

Share This Page