Click for Glendinning List Your Boat Click for Cheoy Lee Click for Abeking Click for Apolonnian

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 Senior Member

    Joined:
    Feb 26, 2012
    Messages:
    776
    Location:
    Ketchikan, Alaska

    We are a bit heavier than that. Prior to any removals, full load was right at 76,000. With an expected weight reduction from the lighter C-18s and gears of 2,000 I used 74,000 lbs as full load for the prop calculation. Not sure how much the additional short ton changes your model?
  2. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,999
    Location:
    Dana Point, Ca
  3. mapism

    mapism Senior Member

    Joined:
    Aug 9, 2008
    Messages:
    1,244
    Location:
    Sardinia
    +1.
    There are many reasons for calling Hatteras great boats, but hull efficiency just ain't one of them.
  4. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    9,579
    Location:
    Satsuma, FL
    I feel the Donzi would have more wet surface over the Hatt.
    Better ride yes but more drag.

    It's a sport hull; there is no efficiency included in these ole bottoms.
  5. mapism

    mapism Senior Member

    Joined:
    Aug 9, 2008
    Messages:
    1,244
    Location:
    Sardinia
    By heart, I would have thought the opposite, but I'm just guessing.
    Do you possibly know which is beamier?
  6. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    9,579
    Location:
    Satsuma, FL
    Without looking up the specs, I'd say the Donzi has the nicer (fat) aft.
    Ya know I'm an aft man.
    logo.png
  7. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,999
    Location:
    Dana Point, Ca
    The older gen 55 Hatt has a beam of 17’-6” beam with a 4’-10” draft including a speed sucking keel.

    The 54 Donzi has a beam of 17’-4” with a draft of 4’-4”.

    The below the waterline cross sections of the Donzi bottom is a better shape for speed and efficiency, with the Hatt having more wetted surface.
  8. Capt Ralph

    Capt Ralph Senior Member

    Joined:
    Sep 8, 2004
    Messages:
    9,579
    Location:
    Satsuma, FL
    That is very interesting. I would not have thought this.

    Well, Ya know,, I got to go for some aft now.
    !cid_16c2848d6f159bf193b1.gif
  9. mapism

    mapism Senior Member

    Joined:
    Aug 9, 2008
    Messages:
    1,244
    Location:
    Sardinia
    Precisely. Good for stability, maneuvering and also hull protection, but surely not for efficiency.
  10. rtrafford

    rtrafford Senior Member

    Joined:
    Jul 13, 2019
    Messages:
    932
    Location:
    Vero Beach
    Exactly. It's a trade off, as I see it. Hatteras was originally designed for sea conditions. You get the ride and the safety in exchange for the wet and the speed with the vintage line. To get to the efficiency you'd need to flatten out the bottom and lighten the load. Modern buyers want both, but that's a very fine line to locate.
  11. rtrafford

    rtrafford Senior Member

    Joined:
    Jul 13, 2019
    Messages:
    932
    Location:
    Vero Beach
    You have to have the draft due to mass and headroom, center of motion, etc...all by design and gravity. The difference, to me in my most simple terms is that the Donzi will eventually run more or less on top of the water while the older Hatt will forever run through it. Hatt's focus a tremendous percentage of HP on lift while Ponzi and other modern designs take advantage of lifting forces within the hull and can dedicate more HP to velocity.
  12. rtrafford

    rtrafford Senior Member

    Joined:
    Jul 13, 2019
    Messages:
    932
    Location:
    Vero Beach
    I put a 53c with modern power through waters and at speeds that would have broken a lot of boats. That big ugly keel fought with my fuel budget on a recurring basis, but when the winds picked up I was always happy to recognize what I was standing on while navigating.
  13. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,999
    Location:
    Dana Point, Ca
    The reference 55 Hatt’s were built from 1980 to 1989 while the 54 Donzi’s were available from 1989 to 1997 and represented a next generation design for that class.
    Draft can be quite a few things, being the lowest measured point below the waterline, and can be the bottom of rudders or props or keel in some cases. Fair body draft is the depth of the centerline of the hull without a keel and would be pretty close for these two boats. Structurally, the Donzi’s have proven there ability to take on seas at higher speeds with better more fuel efficient designed bottom.

    The Hatt’s of that era were just not built for speed with hollow aft hull bottom (concave) sections and the penalty of the keel. They were overweight for their waterline and preferred to bust through seas at the expense of ride comfort/speed. The next gen 55 Hatt came out in 1999 and was a different animal with high hp 3412 Cats and a much higher cruise and top speed, but they have always been known as thirsty designs, even the newer models.

    One benchmark to look at is how much fuel does it take to go 30 knots. Over 90 gph is a thirsty less efficient design, under 90 gph is a much better design and usually has the higher speed potential. The Hatt’s are usually north of 90 gph, some drastically so.
  14. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    13,760
    Location:
    Fort Lauderdale
    ?????? This measure REALLY depends on length. What length are you referring to? 55'? Because the longer the boat, no matter how efficient, if it's a normal SF it's going to consume more fuel to do 30 knots.

    The biggest issue I see with the modern Hatteras SF is the size of their tunnels due to the reduction and props (diameter) they choose to use. I believe they lose a lot of stern lift and some speed because of it. Then again same sized Vikings aren't really any different and they have a different bottom design. I believe it's mostly because the production boats are so heavy compared to the customs.
  15. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,999
    Location:
    Dana Point, Ca
    Length doesn’t matter. Stuffing high horsepower with the resulting high fuel consumption into any design does not necessarily make it an efficient design. 30 knots/90 gph = o.333 nmpg, that’s the magic number. There’s some bandwidth, +/- 10 gph, so the gradient is 80 - 100 gph.

    Consuming 120 gph at 30 knots puts you at 0.25 nmpg and so on, that’s a fuel sucking hog IMO. That’s only 250 nm range on every 1000 gallons, can’t see the efficiency in that.

    Some SF’s are below 0.20 nmpg and that just plain sucks, there is a better way.
  16. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    13,760
    Location:
    Fort Lauderdale
    You'd be hard pressed to do 30 knots in a 90' at 90 gph. Length and associated drag and weight when going larger takes more HP. Yeah, most of the custom SF are very fuel efficient compared to the production SF. Jim Smith's Marlena is very fuel efficient for it's size...….as well as most Jim Smiths, Tribute built Dick Moroso's last Speed Merchant that was very impressive in terms of speed and fuel burn...….Bayliss', etc. etc.
  17. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,999
    Location:
    Dana Point, Ca
    Not too concerned about 90 footers.

    I found a 1995 Boating test on a Donzi 54 and the numbers look pretty good:

    upload_2020-2-17_8-37-38.png

    They even hit my Benchmark criteria for 30 knots at 90 gph or less!
  18. DOCKMASTER

    DOCKMASTER Senior Member

    Joined:
    Feb 26, 2012
    Messages:
    776
    Location:
    Ketchikan, Alaska
    Those are pretty impressive numbers. I see it says full fuel and full water but no mention of total weight. I’ll bet the boat had no tower or hard top, no fly bridge enclosure, probably empty galley, no tackle, etc. It would also have to be light to swing those 32x45 5 blade props. However, it does give me some comfort that maybe the 32x39.5 props I’m going with might be OK. Will see in a few months I guess.

    I didn’t see anyone jump on your over/under pool though PB
  19. PacBlue

    PacBlue Senior Member

    Joined:
    Jan 9, 2009
    Messages:
    1,999
    Location:
    Dana Point, Ca
    I think you are in good shape, the Veem propellers are a not so secret weapon in getting to your speed targets. Makes me want to stick with my initial numbers.
  20. Capt J

    Capt J Senior Member

    Joined:
    Jul 11, 2005
    Messages:
    13,760
    Location:
    Fort Lauderdale
    Call bob roscioli and ask him, but I bet the boat had a hardtop and outriggers. If you look at the photos in the article, that is how the boat wouldve been when they did their test. Inside of the boat would’ve been empty of any additional gear (tackle, galley stuff), but every speed test I’ve done for any manufacturer is without trim tabs, so usually another knot or two above test data IRL guess that accounts for the additional owner weight. My guess is unless you have a tower AND a lot of gear you may be slightly underpropped, and your speed numbers on the light side of actual. Will be very interesting to see.