prop issues :(

[jdblya]

Hey guys

I have a 1995 Four Winns 195 Sundowner cuddy. It is powered by a Ford 302 (5.0) EFI engine. Actual model is a 5.0Fi .Volvo/OMC and has an SX drive 1.51. According to the original specs, it was rated at 220hp and recommended prop was 14-1/4 (I think) x 21p. Currently I have a Michigan Ballistic 14-3/8 x 21p stainless prop. WOT says it should be 4600rpm in the manual. With this prop I have know, I can run about 5200rpm and anywhere between 50-54mph gps. However, I don't like spinning the engine that fast. I was thinking about putting another brand 23p stainless prop on it in hopes that it will lower my wot rpm, and possibly lower the rpm while crusing to get a little better fuel economy. However I don't want to lose all my power out of the hole either.

People are telling me that the engine won't turn a 23p prop. I've even installed another tach to make sure that my tach is accurate and they are within about 100rpm all the way through so I believe that my engine is spinning that fast.

I'm not sure if that certain prop has different characteristics that would allow it to rev higher? but I am hesitant in spending $300 on a 23p prop if it is not going to give me what I want.

Any opinions? I think I am sold on an Stiletto Advantage II, but still unsure if I go with the 23p or stick with another 21p.

Also, on a side note, I've done numerous searches with little info on Prop Diameter. What actually happens if you go from say a 14-1/4 diamter to a 13-7/8?

Thanks in advance.

 

[Capt'n Chris]

Re: prop issues

Nothing noticeable.

 

[fossill]

Re: prop issues

Something wrong with your boat if it wont spin a 23. I'd go for the 21 though for hole shot.

 

[fossill]

Re: prop issues

To further, I'd go for the Stilleto bay Pro II. I like the 4 blade SS props.

 

[hwsiii]

Re: prop issues

Jdblya, I got your pm and as i look at your setup and the prop you are running something doesn't match up. The 220 HP with a 21" ballistic prop at 1.51:1 gear ratio and 5,200 RPM that you are turning with that setup doesn't make sense. I show a different gear ratio for that setup would you please double check that for me. Theoretically the ballistic in a 21" pitch didn't gain but about 100 RPM over the Turbo, Viper or SST in the tests that Ken Sanderson did on his boat, although the slip was more than the rest. I know you have two tachs but 5200 RPMS sounds high for that boat and motor combination.
Would you run it the next time you get a chance and give me the RPM and MPH from 3,000 RPM up to WOT in 250 RPM increments in two different directions and I will run a number of different analysis with that information to try and see what the prop and motor are doing throughout the RPM range, it will help me get a better picture of what is happening.

H

 

[jdblya]

Re: prop issues

Sounds good. I will go and do that for you. The boat is in the water right now, and it is about 50deg and raining, but I will go out there tomorrow. I could be wrong on the ratio, but for some reason that is what I remember reading on the side of the drive.

 

[hwsiii]

Re: prop issues

That sounds good J.

H

 

[jdblya]

Re: prop issues

Ok, after a fun 4th of July weekend, I went out today while everyone was working so I could get some numbers.

First off, the drive is 1:6, I just double checked. Here is what I figured out. I got 500rpm increments instead of 250, because It was a lot of stuff to do at once.


drive down, idle speed. Applying full throttle the rpms run up to about 4000 untill it gets up on total plane which takes just about 4 seconds.

3000rpm with the drive trimmed up a bit, I am running just about 30mph (this is the with the drive about mid trimmed)
3500rpm I'm anywhere from 34mph to 36mph
4000rpm38-41mph
4500rpm 44-46
and today she wanted to run about 5000 rpm wide. I prob could have trimmed it a little more and get that 5200rpm but I don't like running it that high.

and at 5000rpm I was hitting 52-53mph

It almost seems like while on plane I'm almost running mph the same as rpm. ex 35mph 3500 rmp, 40mph 4000rpm and so on. Not exactly, but pretty close.



I hope this is in enough info.

Thanks again!

 

[hwsiii]

Re: prop issues

I would go with the 23" pitch to get the RPM down some.

H

 

[jdblya]

Re: prop issues

Does the Stiletto sound like a good choice in that 23p?

 

[hwsiii]

Re: prop issues

JD, I don't know why your boat is turning the RPM it is at this point or why it is getting the speeds that it is, unless the motor has been rebuilt to a much higher horsepower than it originally was and that would explain the extra RPM or the boat has a pad like a bass boat. Here are the original factory tests for your 1995 195 Sundowner showing a top speed of 49 MPH with a 21" prop and usually these test results are very optimistic. But you seem to be showing a 4 MPH increase over this. I don't have an answer other than what I stated.

But with the numbers you gave me it appears you can run a 23" pitch prop and theoretically you should be turning about 4,750 RPM just depending on the prop you decide to use. When you change props you also are changing blade geometry and there is no way to know how much that will affect the final RPM. But from looking at Kens(Walleyehed) test I see that the SST and the Turbo will have the same RPM but higher speeds. I also ran the numbers for Real Prop Slip and they are not very good, they are too high. There are props for your boat that should produce prop slip somewhere in the the neighborhood of 10% at WOT and more like 13% for the lower RPM instead of the 20% you are getting now.

Real Prop Slip

From my perusal of Ken's prop testing of 21" pitch props the Ballistic prop had the LOWEST speed and the HIGHEST prop slip of all 5 21" pitch props he tested, that is why I charted all of his prop tests so we would be able to use them to compare one prop to another. If you will look at the charts you will see that in every test and all pitches it falls at the bottom of the list for speed and prop slip.

Prop Test Results

http://forums.iboats.com/showthread.php?t=328402


I do not know if the stiletto is the best prop for your boat or not, but maybe dhadley will see this and answer that for you.
I hope you appreciate the time and effort I put into this and let me know the final outcome of what prop and the WOT RPM and speed you get with it for my database.



H

 

[Dhadley]

Re: prop issues

The Ballistic tends to slip a lot but your speed numbers are decent. I wouldn't be surprised if you can swing a 23 Stiletto given the numbers. The Stiletto Advantage is a real good prop with decent lift. The Advantage Plus has a bit more diameter and was meant to be run a little higher (hard to change the X dimension - height - on a sterndrive). The Bay Pro II is a (relatively) small diameter 4 blade and the Bay Pro III is a larger diameter 4 blade.

All of those props has great lift but I suspect the Bay Pro III wouldn't work that well on a sterndrive. We have to jack them pretty high with an outboard.

I know where there's a Stiletto Advantage 23 that may work for you. It's hubbed for OMC 15 spline. Your SX should be a 19 spline hub, check that out and let me know. You could always change the hub, no big deal for any prop shop.

 

[hwsiii]

Re: prop issues

JD, I would definitely go with Dhadley's suggestion. Nobody else on here is as qualified as he is in this genre.


H

 

[ramster]

Re: prop issues

I have a Stilletto for an SX drive that is like new, it's a 14.25X21 I can spin it to 4600 rpm @ 55 mph with my 19 ft. Glastron 5.0. I use an Apollo four blade 20 now because I alway's have at least four people and I ski, tube, and wakeboard. The four blade works better for me, but if you want speed, the Stilletto works great. I was going to put it on Ebay, let me know if your interested.