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  1. #1
    Petty Officer 1st Class bijou22's Avatar
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    Default Converting to Duo-Prop

    What is the procedure for converting a single prop system on a 1997 Cobra SX leg VP 4.3GL, to a Duo-prop system?
    What are the advantages of this conversion?
    Is it worth it and at what cost?
    Wellcraft 21sl Excel 1997
    Volvo Penta 4.3GL
    Cobra SX leg

  2. #2
    Supreme Mariner bruceb58's Avatar
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    Default Re: Converting to Duo-Prop

    Not sure what the lower half of the leg will cost but as far as performance you would notice improvement getting up on plane. The gearing is very different from the single to the duo on a 4.3 so you have to look into that. I am not certain but you may have to change the gears in the upper.

    Keep in mind also that a set of props is $1200 retail. You can get them discounted at $1000 but still very pricey.

    For the age of your boat it would seem to me it wouldn't be worth the investment.
    1998 Wellcraft Eclipse 24 Cuddy
    Volvo Penta Duo-Prop 7.4L "LK"

    2006 Sun Tracker Party Barge 21
    Mercury 90 4-Stroke FI
    "Common sense is not very common"
    "Failing to prepare is preparing to fail." -- John Wooden

  3. #3
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: Converting to Duo-Prop

    With the new prices, a set of aluminum props for a Volvo DP (D4 set) is $699 Suggested retail price from Volvo.
    SS set is $1349.
    Published info on the DP compared to the single prop is about a 25% overall increase in effeciency.
    There is also better fuel economy, better low speed steering etc.
    Is it worth the cost? Only you can answer that, it's your boat and money.
    Don S.


    Please, no PM's (Private Messages) regarding boat/engine problems.
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  4. #4
    Petty Officer 1st Class bijou22's Avatar
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    Default Re: Converting to Duo-Prop

    Thanks guys thats very helpful. Apart from the props, what other costs are involved?
    Wellcraft 21sl Excel 1997
    Volvo Penta 4.3GL
    Cobra SX leg

  5. #5
    Fleet Admiral WillyBWright's Avatar
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    Default Re: Converting to Duo-Prop

    Does that mean that a standard VP SX lower gearcase will swap-out to a DuoProp lower gearcase? Would that mean you could also do it to an OMC Cobra SX?
    Hey, Have you seen? They make Really Cool life preservers nowadays.
    So "Looking Dorky" is no longer an excuse for not wearing one.

  6. #6
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: Converting to Duo-Prop

    That means you can change a Volvo SX to a Volvo DP-S by using a DP-S lower unit.
    No, it won't fit on a Cobra. The outside may look close to the same, but noting inside is the same.
    The shifting is done in the upper on the Volvo's. Water and oil passages are completely different.
    Don S.


    Please, no PM's (Private Messages) regarding boat/engine problems.
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  7. #7
    Petty Officer 1st Class bijou22's Avatar
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    Default Re: Converting to Duo-Prop

    So what I need to look at is a new prop set up and a new lower gear case for an Cobra SX drive. Does anyone know approximate costs of the lower case?
    Wellcraft 21sl Excel 1997
    Volvo Penta 4.3GL
    Cobra SX leg

  8. #8
    Supreme Mariner bruceb58's Avatar
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    Default Re: Converting to Duo-Prop

    Take a look at ebay to get a general idea. Looks like for $3K to $3.5K you can get a used one.

    Not sure I would buy any of them though.
    1998 Wellcraft Eclipse 24 Cuddy
    Volvo Penta Duo-Prop 7.4L "LK"

    2006 Sun Tracker Party Barge 21
    Mercury 90 4-Stroke FI
    "Common sense is not very common"
    "Failing to prepare is preparing to fail." -- John Wooden

  9. #9
    Fleet Admiral WillyBWright's Avatar
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    Default Re: Converting to Duo-Prop

    DonS, the SX drive was a VP/OMC joint venture. That's why the Volvo Penta drive looks so much like a Cobra. They're basically Cobra-like shells with VP-like internals. My bit of confusion with this post is bijou22's combining the word Cobra SX drive and Volvo Penta. There are Volvo Penta SX drives and OMC Cobra SX drives. Different names, same drives (I think). They both have cone clutches and they use the same props. I've never seen a DuoProp lower put on an OMC product, but if the lower gearcase is all it takes to convert a conventional VP SX drive to a DuoProp, I am wondering if a DuoProp lower would also fit onto an OMC SX drive upper. ( Not the conventional Cobra drive that shifts in the lower gearcase. )
    Hey, Have you seen? They make Really Cool life preservers nowadays.
    So "Looking Dorky" is no longer an excuse for not wearing one.

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