Prop measurement

[danfrompgh]

I recently bottomed out and dinged my prop (yeah like thats never happened before,huh?) I've read other postings on this question but most were more confusing than helpful. Here is what I'm working with:
2000 Bayliner 2150 w/5.0-carb, engine is rated at 4200-4400 rpm wot
Boat currently has a 3 blade aluminum prop, runs top speed 50+ at 3800 rpm. I'm not really interested in more speed and planes in 4-5 sec.
I will be needing to replace old prop so my questions are,
Is the prop size & pitch stamped into the hub some where? or how do find this? I would like to keep it close to same.
Is a 4 blade better overall than the 3?
More often than not there is a least one tube or skier behind me and yes $$$ is an issue so I will be replacing with another aluminum.
I can have my toys but she still has the checkbook!!...tks

 

[wire2]

Re: Prop measurement

You get 50+ in a 2150 with a 5.0 at 3800?

WOW! I expect your speedo is a bit on the generous side.

IF your tach is accurate, then you're overpropped a bit. I'll guess you have a 23 on now, should be a ~21. The pitch should be either stamped on the hub (parallel to the prop shaft, the last 2 digits) or in an arc around the nut.

Have a look on eBay, some good deals on props there.

 

[danfrompgh]

Re: Prop measurement

Wire2
I'm guessing speedo is off a little also altho she is out running other boats that say they are doing upper 40's? Us boaters are all kinda BSers !
There are numbers stamped outside of hub,last 2 are pitch?...mine states 23
How bout prop diameter, is it also in the #s?

 

[QC]

Re: Prop measurement

I'm with wire2, but I think a lot of numbers are wrong . . . Speed, no way, RPM, no way . . . If it will only pull 3800 RPM then it is not going 50+ and it would be a biotch to plane if it was a 23". Yes your previous prop was pretty dang good if the speed is even close, so the number in the hub is important and is what you should get if you don't verify those numbers and do this right. Do NOT make any changes until you:

a) Verify the RPM and

b) Verify the speed with GPS . . .

Not trying to give you any trouble, trying to save you some $$$$$

 

[Don S]

Re: Prop measurement

Moving to the Prop Questions and Topics forum.

 

[QC]

Re: Prop measurement

Wow!! Color me stupid, but a 21 with a 5.0 going 50, pulling a 23 . . . ? that engine needs to go to the Smithsonian.

 

[zkimball]

Re: Prop measurement

You didn't say where you were boating or the type of environment, but unless you're purposley using aluminum as an additional shock absorber for frequent bottom knockin', a stainle$$ $teel prop is ultimately the more co$t effective mea$ure. An extra $100 will get you better performance and fuel $avings, and you only have to spend it once! Here in Fl, we live with skinny water, but we have sand or mud, not rocks, so you have to decide. Z

 

[danfrompgh]

Re: Prop measurement

Most of our boating is in W Pa/lakes fairly deep although my running aground was at Shennago resavoir and not marked at all-anywhere. I ended up walking the boat into deeper water after checking for damage,went from 13ft to 1.5ft like...NOW!
All things aside what will a 23 do vs a 21? and still no reply on 4 vs 3 blades. Do you measure prop size from center of the hub to outer edge x 2 or was that bad info also?
I don't need help spending my $$$(stainless vs alum) and really don't care to put my boat into a museum ty,just looking for a non wisearse answer!

 

[Silvertip]

Re: Prop measurement

Diameter may not be stamped on the prop but you can measure that. Measure from the tip of one blade to the exact center of the prop shaft. Then multiply by 2.

 

[danfrompgh]

Re: Prop measurement

Ok gotcha on the prop measurement!..ty
Does 4 blades vs 3 help w/holeshot and prop blowout on turnaround to pickup skier? Not looking for more speed or less actually,whatever the speedo says seems to be plenty fast for us. Just looking for a rule of thumb
Bigger prop vs smaller = ???
More pitch/less = ???
currently (now that I know how to find the size) have 14"-23
does that sound about where I should be with this 2000-2150 Bayliner 5.0?
Runs all day 7-8 hrs tubing,skieing some wot on about 20 gals.

 

[QC]

Re: Prop measurement

Dude, ya gotta verify the tach is correct. It is the only way to select a prop . . .

 

[QC]

Re: Prop measurement

And for the 5.0 Carbed 220 I am finding 4400 - 4800 RPM @ WOT . . .

Also with a 1.62 gear ratio and the numbers above I get 2% slip. Numbers are definitely screwy if it is a 1.62 . . .

 

[Silvertip]

Re: Prop measurement

Wide open throttle at 3800 RPM is lugging the be-jeepers out of the engine. They don't like that and you run the risk of valve problems. Either get the tach verified, get the engine running correctly, or get the correct prop. One or more of those items presents a serious issue.

 

[danfrompgh]

Re: Prop measurement

Silvertip..outdrive is 1:47 type F. By "lugging" the engine I am guessing you mean too much of a load at too low an RPM?
I understand eveyones reasoning behind verifying the Tach & Speedo and sorry to sound repititous but my original questions still stand:
larger diameter prop will result in ????
Lower pitch vs higher (23 -21-19)???
4 blades vs 3...what will I gain/lose ?
I currently have a 14-23..3 blade

 

[zkimball]

Re: Prop measurement

Hey Dan!

No one is trying to skirt your basic questions, it's just you're asking about a lot of variables at once and the result may vary depending on the boat, motor, and application. You just can't give a single blanket answer unless someons owns your particular boat motor etc. But.....

1. Going to a lower pitch will generally give you more power at a higher RPM, like shifting from 3rd to 2nd or 2nd to 1st gear. Less speed, more power.

2. If all the other variables stay the same, a bigger wheel will give you more speed, but.... they won't stay the same! RPM will decrease. What will happen to the power, hole shot, top speed? Can't tell you how it's going to work on your boat; it will be a combination of the two changes. It may work well, but it may not; it's not a direct matematical formula.

3. Four blades will give you a greater grasp on the water. Greater surface area (four blades insted of three) does that. It also costs you in terms of RPM for the same reason. It will certainly cost you in terms of top end, but you might not mind, if jerkin' someone's arms outta the sockets is really what tickles your fancy.

It's a great amalgamation of all these factors. That's the beauty of a forum like this; someone else has been where you are now and they've tried these props and share their results. Any change will cost you something and get you something. You just have to ask several specific questions and then try to cobble all the answers together.

Good luck! Z