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Speed/RPM/Prop questions 1998 Shabah 202

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Old 09-28-2010, 11:13 PM   #1
 
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Default Speed/RPM/Prop questions 1998 Shabah 202

When I first bought my Shabah it was barely breaking 40mph. It has a 4.3L Vortec, I think 195 hp? I advanced the timing a bit (which helped with acceleration and top end) and now have it going at 45-47 on GPS with a 21p aluminum 3 blade prop (newly reconditioned). The rpms are just under 4400.
I was getting about 42-45 at 4600 rpm with a brand new 19p 3 blade, but the holeshot was MUCH better.
Are these numbers right, or should I be pushing a little better performance out of this setup?
A friend of mine has a 1990 Rinker with the 4.3L non-vortec and was able to GPS his boat at 58mph. Ridiculously quick for that setup. I was expecting to get around 52-54 mph alone with no load and low fuel, but I barely TOUCHED on the 48mph mark for a second.
I was considering running a 21p stainless and see if that nets me any kind of gain, but I know the real performance adder will be when I add some trim tabs. I'm hoping to get some Bennett tabs, but if I can't come up with the extra $$ I may just settle for the Nauticus smart tabs. I just worry about wakeboarding and trailering, as they aren't adjustable.
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  • Old 09-29-2010, 12:56 AM   #2

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    Default Re: Speed/RPM/Prop questions 1998 Shabah 202

    Your performance numbers are just about right on for the 202 with a 4.3L in it. The 21" will get you a little more top end at the expense of hole shot and the 19" loses a little off the top but with an improved hole shot. You could consider a 20" - 4 blade which would split the difference.

    Yes....58mph in a Rinky-dink is ridiculous and very hard to believe with a stock 4.3L unless maybe it was a 16-18'.
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    Old 09-29-2010, 01:07 AM   #3
     
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    Default Re: Speed/RPM/Prop questions 1998 Shabah 202

    I agree with Mike. Best I ever got out of my 180 was 49 mph at 4900 rpm with a 21" stilletto prop. That was a cool day and I was the only one in the boat. (Speedometer reading)

    I would run the prop that gets you closest to 4800 rpm. Better performance and less strain on the engine.
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    Old 09-29-2010, 01:43 AM   #4

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    Default Re: Speed/RPM/Prop questions 1998 Shabah 202

    What altitude are you running at?
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    Old 09-29-2010, 07:53 PM   #5
     
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    Default Re: Speed/RPM/Prop questions 1998 Shabah 202

    Elevation is low, probably less than 600' above sea level.

    Thanks for the responses guys, it feels a little better knowing that my boat isn't dogging or far behind the norm. The Rinker is a very nice boat, really well built. I tried to buy it off my buddy all summer before I picked up my Mariah, but he didn't want to sell it til a couple weeks ago. But yeah, it was a 186 just under 19'. The motor was a fresh rebuild on an LX, I believe it was 205hp.

    I think before I get any new props I am going to install some tabs and see where I am at after that...
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    Old 09-29-2010, 08:49 PM   #6
     
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    Default Re: Speed/RPM/Prop questions 1998 Shabah 202

    Yeah, that era of time seems to have had really light weight boats. My dad's '89 Sea Ray was 20'-10" and only weighed 2350 lbs!! But I've never seen a 4.3 hit 58 MPH before!! Is he sure it wasn't on the trailer to the boat ramp when he logged that speed on the GPS? Or maybe the rebuild put a few more horses in the stable?
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    Old 09-29-2010, 10:22 PM   #7

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    Default Re: Speed/RPM/Prop questions 1998 Shabah 202

    trim tabs are only going to help out of the hole and for wakebarding etc. no top end increase. are you trimming the boat properly. my next solution would be to try a 22 four blade if you can borrow one. if necessary 20 four blade. out of the hole great can keep on a plane at much lower rpm's you can take a turn with out losing 2 mph and you might gain a little top end. if you can't borrow one and you have a 21 aluminum have your prop shop punch pitch the leading edge and have him either give you more cup to trim more or run the cup edge after the turn of the blade so it holds the water longer
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    Old 09-30-2010, 03:01 AM   #8
     
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    Default Re: Speed/RPM/Prop questions 1998 Shabah 202

    I figure with the tabs I can afford to run the 21p and pick up some holeshot, hopefully comparable with the 19, because that 19 gets up and out NICE and quick. I've been looking into 4 blade 20p, there's a stainless one in my area for $175. I've heard that you lose a bit of top end with the extra blade, but holeshot is much improved.
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    Old 09-30-2010, 06:40 AM   #9

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    Default Re: Speed/RPM/Prop questions 1998 Shabah 202

    not necessarily so as you did not go down on pitch as some people suggest when you go to a 4 blade. however if you buy the used one make sure that the diameter is what it is suppose to be as when they are repaired more times than not some repair shops cut the diameter to speed up the repair. also check to see if the cup comes all the way around the top. if you are not trimming the boat enough or not sure how much, when the boat is on the trailer put the drive down but even with the boat and mark your trim gauge so you will know where the drive actually is. you will have to learn how to drive the boat with the 4 blade as it tends to push the nose of the boat down. you should be able to trim the boat higher with the 4 blade
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    Old 09-30-2010, 08:11 PM   #10
     
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    Default Re: Speed/RPM/Prop questions 1998 Shabah 202

    yeah this one is brand new, it's just too much prop for his 125 hp yamaha. I trim the boat until the gauge is just into the black about 1/8 of the way, basically all the way up until it comes out of the water too far and slows down the boat/speeds up the motor. I have watched the GPS to confirm that is the best trim angle for top speed.

    The 4 blades have a smaller diameter than their 3 blade counterparts, so I assumed that to be the difference in speed. I asked the guy if he would demo the prop for me anyway, so hopefully it goes well.
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