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Repowering a 54' Donzi Sportfish

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

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  1. Capt Ralph

    Capt Ralph Senior Member

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    Look at who did the test and if it was really knts. Often sales sponsored data is in mph (bigger numbers).
  2. Capt J

    Capt J Senior Member

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    LOLOLOL, hull design and weight. Look up the last Speed Merchant that Tribute built. It was knocking on the 50 knots door step with 2-1000 hp C18's and was 62'.

    There were a few other old SF that were very fast, the 57' Revenge's......the 58' Jim Smiths were deep into the 40 knot range with 8v92's and 700 HP.
  3. PacBlue

    PacBlue Senior Member

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    The one-off custom guys can focus on weight savings where as as the production guys have molds that tend to make heavy laminates unless they are vacuum infused. Plus that beautiful interior runs up the weight scale.

    They usually have less fuel capacity as well, and the Spencer has a fast "bottom".
  4. DOCKMASTER

    DOCKMASTER Senior Member

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    Well I guess I'll just have to stay with my slow boat then. I don't see my wallet supporting a Spencer any time soon........unfortunately. They sure make nice boats. Oh well, back the thread about repowering my paltry Donzi :):):):)
  5. mapism

    mapism Member

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    No clue about how realistic the speed numbers are on that particular boat, but the 67 gph @ 1800 is nothing to write home about, even assuming that she's powered by 1150s.
    According to Cat prop demand tables, your new puppies should burn 28.6 gph @ 1800, i.e. a whopping 10 gallons less than 67, overall.
    Which btw suggests a not so remarkable hull efficiency - but it takes much more data to try to make a meaningful comparison, anyhow.

    Ref. batteries, did your boat have dedicated starting batteries for each engine, maybe?
    If so, I'd consider getting rid of one and use also that space for yet even more house capacity.
    I know that separate starting batteries is a popular setup, but if there is one redundancy which imho is totally useless, it's this one.
    Of course there must be a control allowing to connect the house bank in parallel in an emergency, but I consider that as a given.
  6. rtrafford

    rtrafford Senior Member

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    Consider location of the vessel HVAC raw water supply & compressors? Do they favor that area over another? Recently added a pencil zinc fitting and additional bonding to the intake hose between the sea cock and the strainer. Easy access to maintain, added longevity to the other zincs in the area. Also added a Dry-Bilge system to the lazarette to eliminate as much water as absolutely possible.
  7. DOCKMASTER

    DOCKMASTER Senior Member

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    I have a house bank and two sets of starting batteries. I have to keep it that way. The house bank is 12v and the starting 24v. I also use the starting batteries to power my windlass and the BT which are 24v. Of course, I never use the windlass or BT unless the engines are already running.
  8. mapism

    mapism Member

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    Well, in this case forget what I said! :)
    Out of curiosity, is that a standard Donzi setup?
    I never came across a boat with 24V DC for engines start that wasn't 24V also for house services.
    The only usual exception is the genset, with its own 12V battery.
    But that's irrelevant, of course.
  9. DOCKMASTER

    DOCKMASTER Senior Member

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    Yes, this is standard and factory set up. Pretty common with a lot of builders. I have 12v and 24v buss on the flybridge and main panel as well. Some other builders even added a third 32v set up but I don't think they do that anymore.
  10. Capt Ralph

    Capt Ralph Senior Member

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    24Vdc gen-sets are still available. You can still upgrade your new ones to 24V easily.

    We have 32, 24 & 12 on our boat. All working well but just to many freaking batteries.
    In a couple of years we just may be all 24V. Not because of 32Vdc issues (none), just to many batteries. Then one DC to DC converter/charger and a 4D or G31, 12V battery somewhere for what lil 12Vdc junk that's left.
    This could cut the battery count almost in half.
    16 Batts on board now.
    Last edited: May 1, 2020
  11. rtrafford

    rtrafford Senior Member

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    Ive got both engines with their own starting 24v, and each generator starts off one of the main engine 12's. 2 x 24 for house and bow thruster. one pair of 12v house for navigation and electronics. No house on the engine 24's as don't want any low voltage issues on sensitive systems. Everything charges off 130amp alternators or via the constavolt system. Lots of duplicity. Reduced what was 3 x 32v banks plus 2 x 12v generator starting batteries to 4 x 24v banks and a 12v. 12v could likely be eliminated over time, all to the house 24v.

    Big plus was the two 24v starting banks and picking a 12 off each for each generator. Everything Odyssey. All lighting to LED helps a ton. Still want to add a 24v DC primary chiller at around 2 ton.
  12. mapism

    mapism Member

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    Interesting. Multi-voltage battery banks aren't actually that common, among EU builders.
    Wherever 12V-only components are present in an all-24V boat (mostly for some instruments), they are typically handled through DC-DC converters.
    Another trick sometimes used to facilitate the use of 12V bulbs in 24V boats (particularly before multi-voltage led bulbs were available, and most lights were halogen) is to wire them in pairs, each with a serial connection.

    Anyway, nothing wrong with separate battery banks (and chargers, consequently) for 12 and 24 volts, of course.
    And I can imagine that re-wiring a whole boat designed with that logic can be a big job, maybe not worth doing.
    At the same time, it's an additional complication which is nice to get rid of, if feasible.
    In this sense, I certainly understand why CRaplh is thinking to refit his boat for 24V-only.
    I always thought that whoever invented the KISS principle must have been an experienced boater...!
  13. Capt J

    Capt J Senior Member

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    It IS for a sportfish. Cruise RPM is going to be around 2050 and 33 knots at 86 GPH on that 57' Spencer (2.6 GPNM), 1800 is just efficient cruise. Just do the math, at 1800 rpms the 57' Spencer is burning 2.4 GPNM at 1800rpms/67 GPH with an old hull...…….

    In comparison a new Hatteras 59' GT is doing 26-28 knots at 89 GPH at 1800 rpms 3.3 GPNM, 2100 32-34 knots at 126 GPH or 3.8 GPNM with the base C32/1600 HP cats (taken from Hatteras performance sheet). Most all of the custom SF boats are as fast or faster than the production boats, utilizing less HP and 2/3 the fuel burn per mile...….most do hold as much fuel, or if less, still have the same or better range due to the increased efficiency. The interiors are just as nice if not nicer than the production boats just not heavy. To put this into perspective the Hatteras 59' GT or 58' Viking burn as much fuel at their 35 knot cruise, as a early 2000's 75' Jim Smith SF with full tuna tower that I once worked on at it's 35 knot, 150 GPH cruise.

    What I've seen from the production builders is they made great efforts to reduce weight in the hulls, and some in the FB area's, but then they lose all of that savings by still building a very heavy interior. For example the custom guys will take a 2" thick granite kitchen counter and cut it down to 3/8" thick (+/-) and adhere it to a lightweight coring material so you still have the 1 piece 2" bullnose yet it's 15% of the weight, whereas the production builder will take the 2" thick granite counter top and install it.
  14. mapism

    mapism Member

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    I did some math, actually. That's why I checked the Cat specs for the C-18, according to which two of them should burn 57 GPH at 1800 rpm, not 67.
    Now, I'm well aware that prop demand curves are just estimated, and they are only valid when applied to displacement boats, if you are interested in the whole rpm range.
    But in my experience, if we leave aside the transition speed when a planing boat is not yet over the hump, they are a decent reference also for planing hulls.
    Which for 2300rpm max engines like these, normally means anywhere north of 15 /16 hundreds.
    Anyway, no 57' hull could ever make 28kts without being steadily on the plane, so in the conditions that we are debating for that Spencer, a comparison with the engine manufacturer prop demand curves at 1800rpm does make some sense, for a rough estimation of her efficiency.

    And I'm talking of efficiency in absolute terms, mind - not related to speed.
    That's why I didn't considering GPNM numbers.
    As an example, let's assume to have two different boats A and B, powered by the same engines, both achieving the same speed and burning the same amount of fuel at WOT (obviously, since in both cases the engines are running at max rpm and 100% load) . Let's say that they also make the same speed at 2000rpm.
    At this point, you could think that A and B must have both the same fuel burn at 2000rpm, but evidence shows that this is rarely the case.
    Depending on the hull shape, weight, and other factors, it could well be that the prop demand in boat A is higher than in boat B at that specific speed, and this translates in a higher engine load for the first, hence eventually a higher fuel burn.
    Now, matching exactly the engine manufacturer's curves at any cruising speed can only happen by coincidence, of course.
    But I am indeed aware of planing boats whose fuel burn at cruise speed matches nicely the manufacturer prop demand curves, as well as others where the fuel burn is significantly higher, or also lower.
    And this can only be due to different overall efficiency, all other things being equal.

    Anyway, if we want to bring back speed into the equation, in order to consider fuel efficiency vs. distance and range, we must also consider weight, otherwise 2.4 GPNM means nothing.
    According to a review which I found online, the Spencer 57 weighs 47k lbs.
    Wich is impressive I must say, because my boat, of similar size and with lighter engines, weighs 59k lbs, no less.
    But in spite of that, at the same speed, I "only" burn 2.1 GPNM.
    Bottom line, also in this respect I'm still not hugely impressed by those Spencer 57 numbers.
    My experience with Sportfish boats is very limited though, so if you tell me that she's better than average in this specific category, I take your word for it.

    I'm really looking fwd to hearing from Dockmaster about his own findings upon seatrial.
  15. DOCKMASTER

    DOCKMASTER Senior Member

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    Progress continues. Settee, dinette, TV Lift Cabinet and misc stuff back in now. We also received the exhaust which was the last bid item we were waiting on. The exhaust sure eats up a lot of space! The electrical work is coming together nicely. Getting down to lots of little details and starting to double/triple check all connections. Salon headliner still scheduled for Monday 5/11 followed by carpet on 5/18. Sorry, no idea why it keeps turning the exhaust photos upside down?

    E8425355-A89F-4EE3-B5C3-BF461E7C8F9F.jpeg 21259CB0-0794-4CA8-AFC7-E3E4E66641E2.jpeg 21259CB0-0794-4CA8-AFC7-E3E4E66641E2.jpeg 63470533-BE17-4735-95FC-02124FA48AD9.jpeg A3B45E89-D17F-4CCD-B11B-56C0B32A93EA.jpeg
  16. Capt Ralph

    Capt Ralph Senior Member

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    My fault. I found your temp liquor locker. Oh, Good stock..... Hic-up...
  17. DOCKMASTER

    DOCKMASTER Senior Member

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    We are getting closer every day; and every day brings issues to resolve. Exhaust is all in now-finally!. The supplier screwed up and sent us FRP surge tees that were open on both ends and they didn't include the hoses and clamps to connect the tee's to the exhaust tubes coming into the engine room. They wanted me to ship the tee's back to them and they would ship the correct one's with the dome cover on the fwd end. I told them hell no, that will take a month. I got them to air freight us the dome covers and missing hoses and clamps. We glassed the covers on the tubes and gel coated them and good to go. We also had to modify the inlet on the stbd surge tee. We screwed up when we measured as the 20kw gen was not in place then. The gen actually sits right over the top of the exhaust and the 45 degree inlet on the surge tee interfeared with the gen. We cut the FRP, mitered it to 52 degrees and moved the inlet fwd slightly. Re-glassed it all and gel coated and fits like a glove. Now that the exhaust is all in we can install the two refrigeration compressors and both Racor fuel filter assemblies and other misc stuff that was waiting on the exhaust.

    Insurance company is being a total PITA! They won't let me put the boat in the water without a survey. Surveyor asks me "how do you want me to survey out of the water with none of the equipt. commissioned and functional?". Insurance says, "just give us a survey and make whatever notes surveyor deems necessary." ARGH! It's getting done but what a waste of time and $$. Guarantee they will make me survey again once everything is done and commissioned. Ironically, this is the same underwriter that carriers all of our shipyard business policies. I asked them why they are OK with us putting billion dollar Navy destroyers back in the water without a "survey" but they somehow have determined this 54' boat is a high risk and we suddenly are a bunch of idiots that don't know how to do this type of work? They had no answer.

    Headliner is progressing and carpet being ripped out up forward and new starting to go in. Still have lots of misc electrical and finish work to do. Splash still scheduled for 6/2. CAT is scheduled for initial start -up and trials starting 6/8. This gives us several days to get the new gens, steering, watermaker, etc tested and everything else back on the line.
  18. DOCKMASTER

    DOCKMASTER Senior Member

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    For those of you who like pictures. Exhaust is now complete (2.5" raw water discharge hose still remaining), shaft seals done. And the surveyor didn't like plastic strainers on the intakes in the Laz feeding 9kw gen and raw water washdwon. Replaced with bronze strainers.

    IMG_3280.JPG IMG_3281.JPG IMG_3282.JPG
  19. DOCKMASTER

    DOCKMASTER Senior Member

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    more pics....

    Attached Files:

  20. DOCKMASTER

    DOCKMASTER Senior Member

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    Last ones of this group.... IMG_3285.JPG IMG_3286.JPG