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.
     
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  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

    921
    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.
     
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  8. DarkJester

    DarkJester Active Member

    185
    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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  9. Handsome Transom

    Handsome Transom Active Member GOLD Sponsor

    329
    Jan 26, 2018
    Penetanguishene Ontario Canada
    1989 SeaRay Sundancer 268 454 Bravo
    454 Mercruiser bravo drive
    My 1989 268DA has the 454 bravo 1 drive they used a b1 drive in 89 after too many failed alpha drives from the 3 previous years if this model
     
  10. susanandlance

    susanandlance Well-Known Member PLATINUM Sponsor

    Feb 10, 2011
    Florida
    2007 Sea Ray 36 Sedan Bridge
    8.1 mercruisers
    Your not going to blow a B1 with a 454 that's for sure, don't try to make it a speed boat because it will never be one, top rpm's for that engine is around 44-4600, prop it to where it can hit the max or close to it and cruise it at 3500 rpm's and enjoy it, it's all about the ride not how fast you can get there. If you want to cruise at 40 mph go get a Fountain.....lol
     
    Last edited: Jun 2, 2019
    JVM225 likes this.
  11. susanandlance

    susanandlance Well-Known Member PLATINUM Sponsor

    Feb 10, 2011
    Florida
    2007 Sea Ray 36 Sedan Bridge
    8.1 mercruisers
    I'll bet you that beer, 268's were plentiful with single engines
     
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  12. dwna1a

    dwna1a Well-Known Member PLATINUM Sponsor

    Apr 23, 2012
    James River
    88 Weekender 300 "Seahorse"
    Twins 350
    Lazy would know much better than I but I'd like to suggest this. One of the great Captains here gave me the great name of a prop company, Black Dog Props out of MD. You need and must have all your info in order and submit it to them. They can point you in the direction you are looking for. Welcome and good luck
     
  13. El Capitan

    El Capitan Member

    283
    Jul 9, 2014
    Chicago IL./Vero Beach, Fl
    1970 SRV 180 w 2.5L Mercruiser.
    2000 Ford Expedition Eddie Bauer
    120HP Mercruiser
    If you want to go from 45mph at 5000 rpm to 45 mph at 4000 rpm you’re going to need a bigger prop.
    Guessing here since you have a 450 hp engine and assuming you have a BI outdrive a 23 inch pitch is the neighborhood you’re in.

    Of course, this is all speculation because you don’t know what outdrive you have nor the size prop you’re spinning.

    Limited info = limited answer.
     
  14. susanandlance

    susanandlance Well-Known Member PLATINUM Sponsor

    Feb 10, 2011
    Florida
    2007 Sea Ray 36 Sedan Bridge
    8.1 mercruisers
    Depends on the B1's gear ratio as well
     
  15. El Capitan

    El Capitan Member

    283
    Jul 9, 2014
    Chicago IL./Vero Beach, Fl
    1970 SRV 180 w 2.5L Mercruiser.
    2000 Ford Expedition Eddie Bauer
    120HP Mercruiser
    I may be mistaken but I was under the impression the OP has a B1. I was referring to my experience w a 454/300hp + B1, I ran a 21.5 in pitch on a 1980 SRV242. 30mph @ 3000 rpm, 40 mph @ 3900 rpm. WOT 44 mph @ 4400 rpm by handheld gps.
     
  16. susanandlance

    susanandlance Well-Known Member PLATINUM Sponsor

    Feb 10, 2011
    Florida
    2007 Sea Ray 36 Sedan Bridge
    8.1 mercruisers
    But a B1 comes in several different gear ratio's, and if his is different than yours (very likely) it could mean big differences on prop pitch selection. Ask me how I know, I had a 2005 Fountain 27 with 425 HO, that boat came with different B1 gear ratios, 2.1, 1.65 etc etc
     

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