New to this forum I have a prop question.

Discussion in 'Who's Who' started by Mramps, May 14, 2019.

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  1. Mramps

    Mramps New Member

    2
    May 14, 2019
    268 Sundancer 1989
    454 450hp
    I have a 1989 268 Sundancer. I had the 454 engine rebuilt to 450 hp. I am getting 45 mph at 5000 rpm. It has the original out-drive. Is there a different prop I can install to get more towing/speed at a lower rpm? Any advice would be great.
     
  2. Stee6043

    Stee6043 Well-Known Member

    Jun 1, 2015
    West Michigan
    1997 Sundancer 400
    7.4L Gassers
    Yikes....450hp on the original outdrive? I assume that's a Bravo III? You've got a pretty beefy boat for a single engine and that drive is likely already crying for help. Proceed with caution! I think you're going to want a new drive, not a new and more torquey prop.

    I've detonated the u-joint in an Alpha I drive once. The result was a tad bit of water entering the boat at a highly uncomfortable rate. Highly...uncomfortable.
     
    susanandlance likes this.
  3. JimG

    JimG Well-Known Member SILVER Sponsor

    Nov 4, 2008
    Southern WV
    2007 310 DA
    Kohler 5ECD
    Twin 350 Mags
    Raw Water Cooled
    V-Drives
  4. Espos4

    Espos4 Active Member

    833
    Jan 1, 2017
    Long Island NY
    2007 240 Sundeck
    350 MAG Bravo 3 W/DTS
    Yikes is right. B3 and 1989 seem to be mutually exclusive. Maybe a B1 or B2?
     
  5. Lazy Daze

    Lazy Daze Well-Known Member TECHNICAL Contributor

    Apr 21, 2009
    PA
    Various
    Various
    First, as others mentioned, the drive model is important. If it's an Alpha, all of this, unfortunately, is a relatively moot point. Or, at least, it will be in short time. Alphas ONLY have a possibility of surviving behind a big block when they are babied. Even then, it's sometimes a gamble.

    Which drive do you have? Hopefully it's a Bravo - either B1 or B2.

    Second, 'towing' (hole shot) and 'speed' are opposite things. You can't have both with one prop. Some props bridge the gap a little better than others, but generally speaking they are mutually exclusive to each other. Which one is more important to you?

    EDIT: Based on the work done, what RPM range do you feel comfortable turning?
     
    Last edited: May 14, 2019
  6. Mramps

    Mramps New Member

    2
    May 14, 2019
    268 Sundancer 1989
    454 450hp
    I really appreciate all the great advice When we broke in the motor last month, the mechanic had the horsepower up to 5000 RPM and we were doing 40 miles per hour. When we were driving the boat, the mechanic mentioned we need a bigger prop. He is a very highly respected mechanic and I'm sure he took in consideration the size of the outdrive. The trouble is though that is extremely hard to get ahold of. I would like to be able to do 45 miles per hour at 4000 RPM I do have all the paperwork for the boat. I will see if I can find more information on the outdrive. The boat is in really good condition for its age. It be a retirement project.
     
  7. Lazy Daze

    Lazy Daze Well-Known Member TECHNICAL Contributor

    Apr 21, 2009
    PA
    Various
    Various
    You didn't answer the question of what is more important, hole shot or speed... but since you didn't address hole shot and only talked about speed, I'll assume that's the important thing.

    This is going to be a very tall order. That boat probably originally had a top speed of somewhere in the mid to upper 30's, at about 4500RPM. You added 500 RPM and only gained a few MPH. Now you want to drop 1,000RPM and GAIN 5MPH. You're fighting a hull design that was never meant for top end - it takes incredible HP to gain speed on a hull like that. Probably much more than you're pushing out now, for sure. Yes, you can put a bigger prop (higher pitch) on there and drop your RPM to about 4,500 while "maybe" keeping the same speed at that RPM. But keep in mind you will absolutely be losing hole shot.

    I'm not saying don't experiment - start with about a 3" or 4" in pitch - but what you're after might be tough, if not impossible with that boat.
     
  8. DarkJester

    DarkJester Active Member

    164
    Jul 26, 2011
    North Alabama, Guntersville lake, Tennessee River
    2011 270 SLX
    Merc 8.2 MAG Bravo III
    I'm with Lazy on this. I think you are going to be fighting the hull design to get a "Go Fast Boat" out of a "Cruiser". Prop tuning is tough, guys make tons of money doing it. You gotta pick a poison, hole-shot, or Top-End. And you gotta check your outdrive. Unless you have a super-built Alpha, like Gamma Radiation treated Alpha, 400-450HP is going to wreak Havoc on that puppy. Was the Twin Engine an option on this boat? I would have bet a beer the 268's were twins.
     

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