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Arneson Surface Drives

Discussion in 'Props, Shafts & Seals' started by 993RSR, Oct 6, 2020.

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  1. Capt J

    Capt J Senior Member

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    Most 2000 or newer sportfish do over 6.5 knots in idle. Just run the vessel on 1 engine and in slow idle mode (if equipped) and generally the wake is just under what's acceptable for idle speed/no wake. I prefer not to use troll mode because gear shifts are delayed and sometimes you need the extra power for maneuvering in a marina, personally, I'd rather bump it in and out of gear as needed. Arnesons give you a lot more than a few knots. Last boat I ran with them, I calculated prop slip, we had 1%. Compare that to 15-25% I've seen on shaft boats it's quite a difference.
  2. NYCAP123

    NYCAP123 Senior Member

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    I agree with not liking troll mode (except for longer no wake stretches). How are Arnesons for running on just one side? Has to be different since not you're not only steering with a surface piercing prop but also with directional thrust. Still my biggest objection to them is service. Up here I can only think of one marina that has any experience with them.
  3. CaptPKilbride

    CaptPKilbride Senior Member

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    Same experience for me running a 68' custom boat with ASD12's and V10-1100 MAN's. 35x39 5 blade wheels, if I was in a no wake zone I just had 1 clutched in. Slight offset on the helm was all that was needed to keep her tracking straight. In tight marinas, just bumping in and out of gear as needed .... lots of time just gliding along with both clutched out, with the occasional bump to correct heading, and keep some way on. Was nice to have all that power and torque instantly available if needed.
  4. mapism

    mapism Senior Member

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    Maneuvering aside, how did that boat perform?
    2200 hp and ASD 12 doesn't sound impressive for a 68 footer.
    The previously mentioned Pershing 65 had 3000+ hp, for instance - and it isn't exactly a speed demon, anyway.
    Not to mention the OTAM 58, which can be powered with up to 4000 hp and ASD 14. Though that indeed is a speed demon...
  5. Capt J

    Capt J Senior Member

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    Arnesons are easy for running one one side as far as tracking goes since you're steering the propeller also, plenty of steerage. Service is relatively easy as everything is accessible outside of the boat and very straight forward. Reverse you don't have a lot of thrust as half of it washes against the transom. Steering at hull speeds takes both hands and some arm torque (unless you have a job stick) because the entire propeller is in the water (versus half when on plane), the steering pump is hydraulic and putting out less help, etc. Also they're hard on motors when going from a dead stop to about 900 rpms, because they're propped based on utilizing half the propeller.....so technically over propped under hull speeds, but very efficient unlike jets, which have a very narrow efficiency range.

    I ran into a Captain of an Otam 58'. had 1650hp C 32's......and Captain did indeed tell me it was crazy fast.......I want to say it would cruise 48 knots or so and WOT 58 knots is what he told me, but I don't remember. It was a small 58' as far as interior accomodations went compared to say the Pershing.....
  6. olderboater

    olderboater Senior Member

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    I'm going to compare two sister boats. A Pershing 62 to a Riva 63, either Virtus or Vertigo.

    Pershing 62'2" Riva 64'2", Pershing Beam 15'9", Riva 15'9". Pershing Laden Displacement 86,000 lbs. Riva 72,000.

    Pershing 2 x 1550 MAN's, Riva 2 x 1360.
    Pershing with Surface drives, Riva conventional.
    Pershing top speed 48 knots, Riva 40 knots.
    Pershing cruise 42 knots, Riva 35 knots.

    Whether that's a significant enough difference in speed to justify the Pershing is a matter of taste and consideration of other factors. When we purchased, we said it wasn't worth it to have surface drives. Now, we had limited experience in that size boat at that time. Today, we'd likely consider it. Instead, for speed, we're getting an AB with jet drives.

    The Pershing is by no means a "Speed boat" or even a true "High Performance" boat. It's a faster recreational pleasure boat. For speed, you'd go to a Magnum 70' and twin 2600 hp MTU's and surface drives and a top speed of 58 knots or you'd go to a center console with triples or quads or more and be faster than any of them.

    Pershing makes a faster boat that is still quite usable and enjoyable by couples and families who boat.
  7. Capt J

    Capt J Senior Member

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    Well the Pershing is 20% faster at cruise and WOT than the Riva while being 20% heavier and only having 10% more HP but same engine weight, so there's that........
  8. olderboater

    olderboater Senior Member

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    70' Otam is about the same as the 62' Pershing with 50 knots max and 40 cruise with 4000 hp. However, the 58' with 4000 hp will run 60 knots WOT and 44 knots cruise.
  9. Capt Ralph

    Capt Ralph Senior Member

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    I have to correct you, the Cat tag states 1652 HP.
    The owner of the boat I worked on had to stress that to me one night.
    LOL.gif
  10. Capt J

    Capt J Senior Member

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    Tell him the only difference between his 1652HP C32's and 1900 HP C32's is flashing the computer. That's the only difference is the computer mapping.
  11. Capt Ralph

    Capt Ralph Senior Member

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    Oh, that has been commented on, but in the last 5 years, only idles it around.
    This boat only made WOT at purchase, to fix a prop problem he thought he had and after Cat rebuilt them to extend the warranty.
  12. CaptPKilbride

    CaptPKilbride Senior Member

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    Top speed 35 knots, cruise at 25 -26 knots at 80% load.
    All in all very tractable when running at slower speeds, not much of a "hump", which was important when operating at night or reduced visibility conditions.
  13. mapism

    mapism Senior Member

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    Ok, that's consistent with the size/power. Not so much with the choice of surface drives, though.
    That sort of performance is well within the envelope of shafts, with no stress at all.
    But each to their own, of course.
  14. CaptPKilbride

    CaptPKilbride Senior Member

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    Well, there are other design considerations when choosing propulsion. Surface drives are more efficient, for one. Other advantages for this particular custom yacht included reduced draft (3.5' as opposed to 6'), and extensive operation in Downeast Maine where entanglement in lobster pot warps is an all too often occurrence for boats with conventional propulsion. Not to mention the rooster tail is wicked cool :cool:
  15. mapism

    mapism Senior Member

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    The efficiency advantage is practically negligible, on a 25kts boat.
    It's well above that sort of speed, that surface drives come into their own in terms of efficiency.
    Or better said, shafts become much less efficient.

    I don't disagree on any of your other considerations, but surface drives can also be spectacularly UNcool when, in rough seas, you occasionally lose 50% or even 100% of the boat thrust, because one or both props are completely out of the water.
    Not that this can never happen with shafts, but it takes a helluva worse conditions than with Arnesons, for any given boat size.
    BTW, that's also the main reason why I would never consider surface drives on any boat under 50 feet or so - and the larger, the better.
  16. 993RSR

    993RSR Senior Member

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    quote: when, in rough seas, you occasionally lose 50% or even 100% of the boat thrust, because one or both props are completely out of the water.

    So is this possible in 4-5' seas running 25 knots?
  17. olderboater

    olderboater Senior Member

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    Depends on the boat. On a 60-80' Pershing, highly unlikely although on a 62' could be possible with a very sharp and banked turn, just wouldn't imagine one doing that in those seas. That's where I'd agree with Mapism on boat size. On smaller, fast boats, I've had a stern drive prop out of the water at speed.
  18. Capt Ralph

    Capt Ralph Senior Member

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    I don't see who made that statement; I can only assume the numbers were a typo or another error.
  19. mapism

    mapism Senior Member

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    I didn't quote any specific wave height because there's much more than that to consider.
    Wave form, frequency, direction - and of course boat type and size.
    Anyway, a half decent 68 footer on Arnesons should still handle 4-5' seas reasonably well, in general.
    But in principle, when cruising at 25 kts in rough seas, I'd like my props to work under rather than behind the boat, in terms of handling/tracking.
    And this becomes more important as the conditions get worse and the boat gets smaller.

    Btw, coming to think of it, the reasoning still stands also at 40+ kts, in terms of handling/tracking.
    But at least, that's a speed at which shafts begin to be significantly lousy in terms of efficiency, while surface drives are entering their own territory.
    As I said previously, each to their own.
    All boats are compromises, and it's always a matter of picking your poison, one way or another...
  20. Capt J

    Capt J Senior Member

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    I’d sure as heck rather have arnesons in rough seas than jets, I’ve been in rough conditions in both and never lost thrust with arnesons and think it would be a spectacular sea in order to do so with arnesons. With jets I slid all over the place and heading swung about 80 degrees while on autopilot and hand steering was worse.