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Thread: Available Duo-Prop

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    Available Duo-Prop

    https://seattle.craigslist.org/see/b...378380823.html
    For those of you that want to upgrade your Volvo it appears you can buy the Duo-Prop outdrive for $1,000 and the propellers for $300. This is someone else's listing. I did this conversion on an AQ260 powered Ski Sporter I owned at the time and it transformed the boat miraculously.

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    Ya but if aint the right props for your boat you will be looking at 1000 to 1300 for props. That is the number one reason I never went D/P.
    A winner is just a loser that got up and did it one more time.
    1959 Biesemeyer - 4pt Hydro Drag - 2013 ACBS Winner - Best Race Boat
    1967 Nova Marine - SuperNova24 - ACBS Winner - 2012 Best Race Boat - 2016 Peoples Choice & Best Non Wood
    1972 John Allmand - Nova 19
    1982 PolarKraft -Jonboat - Crab Killer

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    Quote Originally Posted by f_inscreenname View Post
    Ya but if aint the right props for your boat you will be looking at 1000 to 1300 for props. That is the number one reason I never went D/P.
    That logic would certainly apply if one was buying this (or any) bundle hoping that it would work first time for them but if you're buying new it's a whole different scene .
    I actually got it right on twice . Once with the B3 and then with the DPS/a

    What I'm really curious to hear about is the OP's experience with the miraculous transformation it worked for him ! !
    Just because something's old doesn't mean you throw it away !

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    Quote Originally Posted by Morgan's Cloud View Post
    That logic would certainly apply if one was buying this (or any) bundle hoping that it would work first time for them but if you're buying new it's a whole different scene .
    I actually got it right on twice . Once with the B3 and then with the DPS/a

    What I'm really curious to hear about is the OP's experience with the miraculous transformation it worked for him ! !
    I could pop a skier up without effort. When coming in to the boat lift and putting the drive in reverse it was 100% predictable what the boat was going to do. The dual drive increased my top speed to 60 mph on the GPS. This is with a Volvo AQ260 motor. I could maintain plane at 2,200 RPM.

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    Quote Originally Posted by wwahl View Post
    I could pop a skier up without effort. When coming in to the boat lift and putting the drive in reverse it was 100% predictable what the boat was going to do. The dual drive increased my top speed to 60 mph on the GPS. This is with a Volvo AQ260 motor. I could maintain plane at 2,200 RPM.
    For a long time I was under the belief that D/P units were better suited for larger hulls . I don't know if you've seen me say it before elsewhere but after the total rebuild of my St T It was re-powered with a new 350 Volvo and the single prop SX/a drive . It was virtually un-driveable, to my total shock .
    Playing with props made no difference so I bit the bullet and swapped out the SX/a for DPS/a and it's now a totally different boat.

    After many decades of playing around in moderately well powered single engined boats it was a shocking lesson in how much of an effect a single prop has in throwing the boat around without the driver even really knowing it .
    Just because something's old doesn't mean you throw it away !

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    I would not expect duoprop drives to increase, or even match, top end speed with a single prop. Certainly not if the single was any flavor of Merc. That sounds fairly unusual. (Perhaps itís the case with the old style single prop Volvos though. The ones that have seemed so hydrodynamically limited, hitting a bit of a wall close to or a hair above 60.)

    But Iíd expect dual prop drives perform better in every other way than any flavor of single. Propsets are pricey, but the behavior of the boat is great in my experience.
    "I don't have time to get into it, but he went through a lot." -Pulp Fiction

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    Quote Originally Posted by Morgan's Cloud View Post
    For a long time I was under the belief that D/P units were better suited for larger hulls . I don't know if you've seen me say it before elsewhere but after the total rebuild of my St T It was re-powered with a new 350 Volvo and the single prop SX/a drive . It was virtually un-driveable, to my total shock .
    Playing with props made no difference so I bit the bullet and swapped out the SX/a for DPS/a and it's now a totally different boat.

    After many decades of playing around in moderately well powered single engined boats it was a shocking lesson in how much of an effect a single prop has in throwing the boat around without the driver even really knowing it .
    One of my neighbors here on Lake Washington was Bill Cook a long time Boeing man. He saw what I did with the Duo-Prop and gave me a lesson on turbo prop airplanes. He showed me how a mechanical advantage occurs where these two different diameter counter rotating propellers work. So where it might appear more bulk is moving through the water, the advantage overcomes this in a multiple effect.

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    Quote Originally Posted by wwahl View Post
    One of my neighbors here on Lake Washington was Bill Cook a long time Boeing man. He saw what I did with the Duo-Prop and gave me a lesson on turbo prop airplanes. He showed me how a mechanical advantage occurs where these two different diameter counter rotating propellers work. So where it might appear more bulk is moving through the water, the advantage overcomes this in a multiple effect.
    Thatís interesting. And may well explain whatís typically been seen with dp drives. As you note, there is undeniably more drag. The question becomes whether the counter-rotation creates efficiency to overcome that.

    Aside from old Volvos, it does, except at the highest speeds. At low and midrange speed, prop slip is greatly reduced, and performance is much better at the same rpm. At the highest speeds, single 3-blade props usually get down to slip of 11 percent or less. They have good bite there, thus good efficiency, and the lesser drag of the single prop wins the day for top-end speed.

    On the old Volvos, there seems to be a hydrodynamic obstacle around 60. N2O saw this big-time in his high powered 16. I suppose water flow may get bad at that speed and interfere with the propís grab. The DP might have more bite and might overcome this, if thatís what is happening. And thus might yield a bit more WOT speed, as youíve experienced.

    (Curious Bill, when the Dee used to hit the wall in the low 60s, did the revs seem to climb up without adding speed, suggesting a loss of bite? Or did the drag just seem huge and the motor just wouldnít make more RPM?)
    "I don't have time to get into it, but he went through a lot." -Pulp Fiction

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    I've always thought it a bit interesting that at anything but WOT a d/p produced a higher speed than a single prop . Mind you , there's been a ton of development since the old original Volvo d/p drives were introduced and the majority of the stats originated.

    I'd feel pretty comfortable saying that the old VP d/p was a tad slower than the Alpha 1 and that the B3 is slower than the B1 but the new Volvo technology is way ahead of the old stuff . Both in terms of prop technology and drive hydrodynamics .

    I do know that my St T is not only driveable now but it sure seemed faster as well the last time I tested it . WOT rpm was still a long way off and the thing was frighteningly fast. Maybe one day I'll find out exactly how fast , but it always comes down to the owner making the choice between top speed ( which is only used once in a while for the average person) and greatly improved handling across the entire throttle range.

    It brings to mind Tony who used to have the C22 with the rare 454 DPX package . It was fast AND a dream to drive. I wonder if he ever had a chance to do any head to head comparison with a 454Mag B1 C22 ?
    Just because something's old doesn't mean you throw it away !

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    In 2008 I was looking for 22C. There was one(2000) for sale just outside of Orlando but it was powered with a 454-385 HP with a Volvo DPX and E4 props. I always thought that if you wanted to go fast the drive had to be black. I wasn't a member of this forum at the time so I got a friend of mine(Tim Morris) to make a post asking for feedback on the DPX drive.

    Almost immediately a few guys chimed in. One said that if the Orlando 22C would have available 6 months before he would have been all over it like a fat kid on an Oreo.

    Another guy said that the DPX had integrated power hydraulic steering. And another said that the DPX could take 600 HP. And yet another said that it was about 3 mph faster than the 454-385 Mercury.

    Needless to say I bought the boat and hauled it back to Ontario.

    I did talk to Tony Sporer a couple of times before he sold his 4-5 years ago.

    He told me that GPS top speed on his was just a touch over 73 mph. The best that I've ever got was 71.8 mph with absolutely NO chine walk or porpoising. I have actually taken my hands off the wheel at 65.

    It has about 400 hours on it and still runs really strong.

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    [QUOTE=mc donzi;669149 like a fat kid on an Oreo.

    [/QUOTE]

    I resemble that remark.

    Ken

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    I tested two 502/DPX powered boats at the Miami boat show in '93
    One was a single installation in a Cobalt 25 - almost a maxi cube cruiser , the other was twins in a 31 or 32 Scarab .
    The combination of the integrated hyd steering and the DP effect was enough to make me want to walk out with both of them. And they were amazingly fast as well . Watching a new thrust cone open up in the prop wash when you jabbed the throttle at 4000 rpm and the pin you back in your seat feeling was almost intoxicating.

    Pity they're no longer in production .
    My only issue with the DPX was that at rest the external hyd steering rams were beneath the waterline so that meant that it wouldn't have been advisable to leave the boat in the water for extended periods as the rams would get scaled up and then the seals would be next to go as soon as you turned the unit . Much like what happens when you trim a Merc all the way up and leave it in the water for a good while .
    Just because something's old doesn't mean you throw it away !

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    Yeah, itís a crime that the DPX disappeared. Had they been around, Iíd have put one in during the Cig restoration.
    "I don't have time to get into it, but he went through a lot." -Pulp Fiction

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    Quote Originally Posted by Ghost View Post
    Thatís interesting. And may well explain whatís typically been seen with dp drives. As you note, there is undeniably more drag. The question becomes whether the counter-rotation creates efficiency to overcome that.

    Aside from old Volvos, it does, except at the highest speeds. At low and midrange speed, prop slip is greatly reduced, and performance is much better at the same rpm. At the highest speeds, single 3-blade props usually get down to slip of 11 percent or less. They have good bite there, thus good efficiency, and the lesser drag of the single prop wins the day for top-end speed.

    On the old Volvos, there seems to be a hydrodynamic obstacle around 60. N2O saw this big-time in his high powered 16. I suppose water flow may get bad at that speed and interfere with the propís grab. The DP might have more bite and might overcome this, if thatís what is happening. And thus might yield a bit more WOT speed, as youíve experienced.

    (Curious Bill, when the Dee used to hit the wall in the low 60s, did the revs seem to climb up without adding speed, suggesting a loss of bite? Or did the drag just seem huge and the motor just wouldnít make more RPM?)

    I don't recall climbing RPM without increases in speed. I do know the overall usage of the boat went up noticeably after the conversion. Initially the props were over pitched but the guy that sold the unit to me was also a Volvo employee. He supplied new lesser pitched props that would let the engine rev out to 5,500 RPM but lower top speed. What ever it was the result was great thus my encouragement to have someone buy this used unit.

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    Interested

    Quote Originally Posted by wwahl View Post
    https://seattle.craigslist.org/see/b...378380823.html
    For those of you that want to upgrade your Volvo it appears you can buy the Duo-Prop outdrive for $1,000 and the propellers for $300. This is someone else's listing. I did this conversion on an AQ260 powered Ski Sporter I owned at the time and it transformed the boat miraculously.
    I have a 1969 donzi with 302 ford with 270 Volvo outdrive I have always wanted a dp set up any help setting me up with what I need and where to get it would greatly appreciated Thanks Jim craw5551@comcast.net

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