1990 Stingray...Do I have the right prop?

Hello... I have a 1990 Sting ray 19 footer. It has a 5.7 v8 with a Yamaha Sterndrive(yes, a yamaha sterndrive!). Right now I am running a 14x23 pitch prop. It seems that with four or five people in the boat I cant get much speed. I can get maybe 40 WOT. When I got the boat I was told it would do 55 Mph. I did hit the prop once but it dont really look very bad. I also have a 14.5x19 pitch that I havent tried yet.
Anybody got any ideas on what I should put on it? where is the best place to buy them? Any help would be great!

Should I take off the 14x23?

Re: 1990 Stingray...Do I have the right prop?

Correct propping is based 100% on RPM.

When you are going at your top speed/full throttle, what is the engine's RPM? And what is the correct WOT RPM operating range of your Yamaha sterndrive?

If you are spinning outside of your operating range (too high, or too low) it is incorrectly propped. If you provide exact speed and RPM data, we can advise what prop should work better.

Re: 1990 Stingray...Do I have the right prop?

Running down the lake WOT its running around 4800,4900 RPM. It screams. Ill check to see what the drive is supposed to run at, but im pretty sure that what I read for a rating on the motor cover.
Thanks for the help!

Re: 1990 Stingray...Do I have the right prop?

Yes, you should find that info on the cover for most brands. The other piece of information we really sorta need is your outdrive gear ratio, so that a prop calculator can be utilized. I don't know where you will find this on your Yamaha. Might be stamped somewhere on the outdrive??

So far At 40 mph, 4900 rpm, and 23 pitch prop, something smells fishy....it just feels like one of these figures is waaaayyy off...have they been verified? Ideally GPS for speedo, maybe a shop tach for rpm?

But it all the calculations hinges on your drive ratio, and I don't have one iota of knowledge about those Yamaha sterndrives. When I run it as a 1.5 drive ratio (which would be fairly typical for a 5.7L in a runabout for a Mercruiser or OMC setup) I get a theoretical top speed of 71 mph. So your 40 makes no sense whatsoever unless it is defying all laws of physics...or, more likely, one of these figures is off...

Re: 1990 Stingray...Do I have the right prop?

I took another look at the top of the motor, And WOT is 4200-4600 RPM. Im going to take the boat out tonight and try it with the 19 pitch prop that is in good shape. Anybody know where I can find the gear ratio for my outdrive?

Re: 1990 Stingray...Do I have the right prop?

I urge extreme caution with your plan there...

If you're turning 4,900 with a 23 pitch, and you intend to test drive a 19 pitch, you have the potential to approach 5,500 rpms or more....on a motor that is not supposed to go past 4,600....

Do you have a way to verify your tach is accurate first? You'll need to keep a close eye on a GOOD tach, to prevent a catastrophic mechanical failure if that 19 pitch is way too low. Make sure you get out of the throttle NOW if you go past 5,000 on that test drive...

Re: 1990 Stingray...Do I have the right prop?

Yep im going to try out out...watch it very carefully. Also going to bring GPS for speed and see if I cant double check the tack. Whats the best way to test the tach? i dont Think my DMM has that option....

Re: 1990 Stingray...Do I have the right prop?

Best way to check the tach is to hook up another...most engine analyzers have them. Some are inductive pickup off a spark plug wire, many others just aligator clip it straight to the coil.

I own one like this:
http://www.actron.com/product_detail.php?pid=16155

Here's another inexpensive one that has inductive pickup:
http://www.google.com/products/cata...=X&ei=yF8bTvXJJ8KFsAKn65jCBw&ved=0CDIQ8wIwAg#

Re: 1990 Stingray...Do I have the right prop?

I took the boat out and installed the 14.5X19 on it. Work just as good as if not even better than my 23 pitch. It ran about 35 mph(maybe a little faster trimmed out) at 4300 rpm. So, my 23 pitch doesnt look that bad, but i suppose it is toasted. Any ideas on what I should buy?

Re: 1990 Stingray...Do I have the right prop?

So you ran 4,900 on a 23 pitch, and 4,300 on a 19 pitch.

With results like that, I have absolutely no idea what to recommend....those results are the exact opposite of propping rules-of-thumb...

And you can only get 35 to 40 mph out of a 5.7L powered 19 ft Stingray? Stingrays are notorious for being FAST hulled boats. So I agree entirely you should be able to to 55-ish, or more, if that motor is running right.

For reference, my 20 foot Stingray with a 5.0L runs 57 mph on GPS. And it's not even propped for speed...it's set up for watersports pulling.

Which makes me seriously wonder if your motor is running right...when was your last comprehensive tune-up and general health-check of this engine? Ignition timing, compression check, etc...

Very sorry, but frankly I'm at a total loss...maybe someone else here can see something I'm missing.

Re: 1990 Stingray...Do I have the right prop?

Sorry about being confusing..... I think i was running 4600 with the 23 pitch. The motor has been gone through, and runs great. What size are you running on yours?... Sorry to take up your time, seems nobody in my area has any idea...


The 23 pitch did strike bottom one, but does not appear to bad, however, I suppose it is. The last owner of the boat had that prop on and he claimed 55 MPH with it. However, when I got the boat, the carb was not working correctly. And even then It would run faster. Then it stuck some rocks. I have gotten the carbn fixed and now it has no speed.
Sorry again about being confusing....Im a newbie to this!

ill also throw in that I didnt hold it WOT, seems to be no govoner. So, I figured id be safe at 4300

Re: 1990 Stingray...Do I have the right prop?

I run a 20 pitch. But that is irrelevant as my boat is entirely different from yours...HP, weight, and presumably drive ratio.

If you haven't done a WOT throttle run, then that explains why your results confused me. Your 4,300/35mph run is a meaningless number, if you backed out of the throttle....

Re: 1990 Stingray...Do I have the right prop?

yes.. I was scared of over reving the motor, I pushed it down once and it did go to 4700

Re: 1990 Stingray...Do I have the right prop?

Then as I suspect, that 19 is simply not enough prop. If you were spinning 4,800/4900 with your 23 pitch, and you're striving for 4,600 or less....then you need more pitch, NOT less. A 19 would risk revving clear up into the upper 5,000's....

25 is a resonable guess for proper pitch. Or maybe a 23 that's not a buggered up. That's totally a guess. BUT...and this is a big BUT: The math on this entire thing still makes absolutely no sense to me...and not knowing your drive ratio makes confirmation of anything extremely difficult.

Here's how to find your drive ratio manually, by turning the engine by hand and counting prop rotations:
http://www.mercstuff.com/drivegearratio.htm

Welcome to the world of obscure/short production run Yamaha Sterndrives...very few people have much knowledge about them, and even fewer know how to fix them when they break....

The other real easy solution, if you think that damaged 23 pitch might just be the correct prop for this boat, is to simply have that prop rebuilt. If it's stainless, it's well worth it and reasonably priced for what you get.