How much does prop condition affect performance?

[airdvr1227]

My prop looks used. A couple of very small dings on the leading edges and the faces of the blades are pitted and the paint is worn off.

I'm wondering how much that affects the overall performance.

 

[hwsiii]

Re: How much does prop condition affect performance?

I can tell you that you have 24% prop slip right now and that is not good, even with a heavier boat like yours. That is causing you major loss in speed with that much slip and I believe you have the wrong prop more than the dings are a problem.


H

 

[airdvr1227]

Re: How much does prop condition affect performance?

Any recommendations?

 

[hwsiii]

Re: How much does prop condition affect performance?

If you will fill this out, I will do an analysis for you.

Iboats Boat and Motor Info

1. Year, make and model of boat
2. Length, width and base weight of boat, look for boat decal on back of boat
2a.What is the maximum recommended HP for your boat
3. Number of people and gallons of gas normally on boat
4. What do you use the boat for
5. Is it a Deep Vee and if so how many degrees of deadrise
6. Year, make. manufacturer and model of motor
7. HP and gear ratio of motor IMPORTANT
If you don?t know the ratio, you need to pull the plugs out and put a piece of tape across the prop and the lower unit and then cut it between the prop and the housing then do the same thing on the motor and turn the motor until the tape lines up with each other on the prop, it is easier if two people do this, so one can watch the prop while the other counts the revolutions of the motor
8. Manufacturer?s recommended Wide Open Throttle (WOT) range
9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches, use a board under the keel and stiking out to the anti ventilation plate for a referene
10. Is it a bass boat or does it have a pad bottom
11. Does it have a hydrafoil, dolefin or trim tabs
12. Make, model, diameter, pitch and whether SS or aluminum prop
13. WOT RPM and speed from your current prop and how much gas and how many people were in the boat for the test data and is the speed by GPS. Make sure you trim the prop up until it starts ventilating and then just trim in until it quits ventilating. If you do not have a tach you can buy a Tiny Tach for $ 50
RPM ___________ Speed ___________ No. of people ____________ Gas ________
14. Are you at sea level or a higher elevation, give us the elevation in feet
15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way, checked compression, and looked at the plugs and checked spark, all of the foregoing could be the reason your prop is not attaining full RPM
16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop
17. Does the prop show any damage that you can see
18. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations
19. If you are trying to attain a better cruising speed and fuel savings or trying to attain a faster speed I will want you to take your boat and run it with 1 or 2 people and give me the RPM and speed readings starting at 3,000 RPM in 500 RPM increments all the way to WOT.

REMEMBER, The numbers I give you will be NO better than the information you give me

The only thing I ask of you is to come back and give me a report of WOT RPM and speed for my database.


H

 

[divimon2000]

Re: How much does prop condition affect performance?

I've had 1/4 of a blade missing from a prop once on a smaller whaler and didn't notice a bit of difference! But I like nice props so i'd dress yours at least.

 

[airdvr1227]

Re: How much does prop condition affect performance?

Thanks! I should have that data on Monday.

 

[hwsiii]

Re: How much does prop condition affect performance?

I will be ready.


H

 

[TahoeQ4Pilot]

Re: How much does prop condition affect performance?

My prop looks used. A couple of very small dings on the leading edges and the faces of the blades are pitted and the paint is worn off.

I'm wondering how much that affects the overall performance.

Here is my recent experience with prop performace: http://forums.iboats.com/showpost.php?p=2281146&postcount=4

 

[airdvr1227]

Re: How much does prop condition affect performance?

Here is my recent experience with prop performace: http://forums.iboats.com/showpost.php?p=2281146&postcount=4

Very interesting. I wish there was a way to 'test drive' a new prop. I already made the mistake of trying to figure it out by using the OEM manual's numbers and taking an uneducated guess. The result was one seriously overpropped boat. Anyone want to buy a 14 1/2 x 21 prop? Used only once :redface: An expensive mistake I won't make again.

I don't doubt that a new prop with the same pitch as I have now (15 1/2 x 15) would improve the performance somewhat. But I hear my 5.8L singing beautifully at WOT and I know my rig has the torque to push out more speed with the right prop. And I'm only gonna buy one more

 

[airdvr1227]

Re: How much does prop condition affect performance?

If you will fill this out, I will do an analysis for you.

Iboats Boat and Motor Info

1. Year, make and model of boat 1991 Chris Craft 228 Concept

2. Length, width and base weight of boat, look for boat decal on back of boat 23.5 feet 8 feet wide 3700 lbs
2a.What is the maximum recommended HP for your boat 230

3. Number of people and gallons of gas normally on boat 2 and 35 gallons

4. What do you use the boat for Speed, tubing, etc.

5. Is it a Deep Vee and if so how many degrees of deadrise N/A

6. Year, make. manufacturer and model of motor 1991 OMC 5.8L

7. HP and gear ratio of motor IMPORTANT 1.41
If you don?t know the ratio, you need to pull the plugs out and put a piece of tape across the prop and the lower unit and then cut it between the prop and the housing then do the same thing on the motor and turn the motor until the tape lines up with each other on the prop, it is easier if two people do this, so one can watch the prop while the other counts the revolutions of the motor

8. Manufacturer?s recommended Wide Open Throttle (WOT) range 4200-4600

9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches, use a board under the keel and stiking out to the anti ventilation plate for a referene N/A

10. Is it a bass boat or does it have a pad bottom N/A

11. Does it have a hydrafoil, dolefin or trim tabs Hydrofoil

12. Make, model, diameter, pitch and whether SS or aluminum prop 15.5x15 Aluminum Mfg unk

13. WOT RPM and speed from your current prop and how much gas and how many people were in the boat for the test data and is the speed by GPS. Make sure you trim the prop up until it starts ventilating and then just trim in until it quits ventilating. If you do not have a tach you can buy a Tiny Tach for $ 50
RPM _4200__________ Speed ___32________ No. of people ____2________ Gas ____25 gallons____

14. Are you at sea level or a higher elevation, give us the elevation in feet 1100 feet

15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way, checked compression, and looked at the plugs and checked spark, all of the foregoing could be the reason your prop is not attaining full RPM Just tuned up but carb is getting rebuilt this winter. I don't think it's affecting RPM's

16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop Prop has been on since I bought it this spring

17. Does the prop show any damage that you can see small dings on leading edge, pitted, paint mostly gone

18. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations Faster!

19. If you are trying to attain a better cruising speed and fuel savings or trying to attain a faster speed I will want you to take your boat and run it with 1 or 2 people and give me the RPM and speed readings starting at 3,000 RPM in 500 RPM increments all the way to WOT.

3000 - 20mph
3500 - 24mph
4000 - 29mph
4200 WOT - 32 mph
REMEMBER, The numbers I give you will be NO better than the information you give me

The only thing I ask of you is to come back and give me a report of WOT RPM and speed for my database.


H

Here it is...thanks in advance

 

[45Auto]

Re: How much does prop condition affect performance?

When is the last time you did a compression check on the motor???

Something is wrong somewhere if you are only turning 4200 RPM on a 15" pitch prop with that boat.

I guess it was overpropped when you went to a 21" pitch!!!! It can't turn the 15" pitch like it should be.

I know my rig has the torque to push out more speed with the right prop

If it had the torque (which is directly related to HP) to push out more speed it would be turning faster than 4200 RPM with a 15" pitch .....

I would seriously check the health of the motor before spending more money on props.

 

[wca_tim]

Re: How much does prop condition affect performance?

the thing that is killing you speed wise on that boat is the gear ratio...

but by the same token, it would be worth borrowing another prop from someone to try. if your blades are bent even a little bit you're losing a lot of energy and probably some speed.

 

[airdvr1227]

Re: How much does prop condition affect performance?

When is the last time you did a compression check on the motor???

Something is wrong somewhere if you are only turning 4200 RPM on a 15" pitch prop with that boat.

I guess it was overpropped when you went to a 21" pitch!!!! It can't turn the 15" pitch like it should be.

If it had the torque (which is directly related to HP) to push out more speed it would be turning faster than 4200 RPM with a 15" pitch .....

I would seriously check the health of the motor before spending more money on props.

I guess I'm a bit surprised by this post. I haven't done a compression check basically because it was all I could do to get the plugs back in the head during the tune-up. Haven't felt the need because she runs strong. Tune-up was to try and alleviate some low speed idle problems that I now believe to be a card in need of rebuild.

According to the OEM manual WOT is 4200-4600 and she's turning 4200 with no problem. Pulls hard from a standing start and sounds sweet at WOT. A little blue smoke when she's cold and defintiely running rich.

Anyone else think my engine could be in trouble?

 

[bigskiohio]

Re: How much does prop condition affect performance?

it could be a throttle adjustment needed to get wot higher but sounds okay to me try another prop you should be 19 or higher. lower is fore getting out of the hole or if under powered.

 

[hwsiii]

Re: How much does prop condition affect performance?

My calculations show you should be getting another 6 to 8 miles per hour out of that boat and motor combination, so something is definitely wrong. And I also show you have a 24% prop slip with the prop you have on there, so after you find the problem come back and we will get you a better prop for your boat.


H

 

[airdvr1227]

Re: How much does prop condition affect performance?

Now I'm confused. You say I have 24% prop slip but my rig is running the correct RPM's. WHat could be the cause of that?

 

[Thad]

Re: How much does prop condition affect performance?

Now I'm confused. You say I have 24% prop slip but my rig is running the correct RPM's. WHat could be the cause of that?

The 4200 is the low end of performance. You really want to get to the high end.

I do not know about where you are at, but here, we have a prop shop that not only repairs but sells.(I just foud out after 13 years of living here) He will let me take a prop out on my boat, run it and report back to him what I think. Of course I will run it by hwsiii first. Then he will let me try another prop. After I have decided on one, he will then "tweek" it to my boat and desires. Again, after running it by hwsiii.
So look around and see if this is available in your area. And listen to hwsiii, he will get you in the right direction and before you know it, wow.
I did not and still do not understand a lot about props, but he and a lot of the other guys do. I trust them and have not been steered wrong.

http://forums.iboats.com/showthread.php?t=329272&highlight=prop+slip+what+is+it
Look at this thread I had posted and I think I got a pretty good answer about prop slip and maybe it will help you understand a little more also.

 

[hwsiii]

Re: How much does prop condition affect performance?

Think of a prop like a screw being turned into a piece of wood, if it is a 4 pitch that means for every 4 turns of the screw it goes into the wood 1". The vertical distance between two adjacent screw threads is called the pitch of a screw. One complete revolution of the screw will move it into the wood a distance of the pitch of the screw or 1/4".
Now lets look at a prop, a 15" pitch prop means that for every revolution of the prop, if it was going into a solid, it would screw into it 15". But since it is in water it can slip, and that is what is called prop slip. When I told you that your prop had a slip of 24% that meant that for every revolution of the prop instead of moving the boat ahead 15" it only moved it ahead about 11.25" and that is what is called prop slip. That is why I said you need a different prop, because the one you have is slipping 24% and we want to get that down to about 9%, which would theoretically raise your speed to 36 MPH instead of the 32 MPH you get now.


H

 

[45Auto]

Re: How much does prop condition affect performance?

the thing that is killing you speed wise on that boat is the gear ratio...

Hi Tim,

Why do you think the gear ratio is so bad? Isn't a standard Alpha V8 ratio a 1.5? A 6% difference in gear ratio would be barely noticable, about the equivalent of 1" of prop pitch.

I haven't done a compression check basically because it was all I could do to get the plugs back in the head during the tune-up. Haven't felt the need because she runs strong.

I wouldn't call 4200 RPM on a 15" pitch prop "strong". It's an 18 year old motor that's not running right, first thing I would do is a compression check. My 1987 30' Sea Ray has twin 5.7L 260 Hp Mercruisers with 1.5:1 Alpha outdrives and 19" pitch High Five props. Port motor would easily turn over 5000 RPM, starboard motor could barely make 4000. Turned out the starboard motor had 150 PSI compression in 6 cylinders and 100 PSI in the other 2. Had a bad ring in one cylinder and a bad exhaust valve in the other. Hoping to get it back in the water this weekend and have both motors running like they should. A compression check is cheap insurance against wasting a lot of money and time.

 

[wca_tim]

Re: How much does prop condition affect performance?

Hi Tim,

Why do you think the gear ratio is so bad? Isn't a standard Alpha V8 ratio a 1.5? A 6% difference in gear ratio would be barely noticable, about the equivalent of 1" of prop pitch.



I wouldn't call 4200 RPM on a 15" pitch prop "strong". It's an 18 year old motor that's not running right, first thing I would do is a compression check. My 1987 30' Sea Ray has twin 5.7L 260 Hp Mercruisers with 1.5:1 Alpha outdrives and 19" pitch High Five props. Port motor would easily turn over 5000 RPM, starboard motor could barely make 4000. Turned out the starboard motor had 150 PSI compression in 6 cylinders and 100 PSI in the other 2. Had a bad ring in one cylinder and a bad exhaust valve in the other. Hoping to get it back in the water this weekend and have both motors running like they should. A compression check is cheap insurance against wasting a lot of money and time.

You're right... had gear ratios on the brain trying to decide what set of gears to put in a drive I just got. definately worth looking at engine issues...