When to replace a prop ? Bent blades ?

StingRay_90V4

Petty Officer 2nd Class
Joined
Aug 26, 2014
Messages
155
So my prop isnt the newest in the lake. That's for sure. It has to be nearly 15 or more years old. Easily. It has a few nicks here and there out of it. None that are overly large at all per say. But one is about an 1/8th or so onto the blade and about an inch or so long. It is the biggest on. So nothong too major. How ever the other two blades are sort of bent in and out a bit at the tip of the blade. Its hard to describe. But small waves in the tips would be my best description. So i was wondering if this type of mild distorted blades and a few nicks here and there are enough to affect the boats performance at all. As in its bite on the water and how it accelerates as well as its wot top speed. I have worked out my slippage and at 43 to 44mph at 5550 to 5600 ish rpm. My slip appears to be around 3 to 4 percent. Os there any sense in replacing the old standard brp prop with another stock brp 17 p wheel ?

Thanks in advance for the advice
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
12,944
Any deviance from the perfect blade shape/contour will result in a performance drop. How much? It can be as little as 1/10 mph or severe enough to keep the boat from planning. Of greater concern is the props balance. Out balance props can play havoc on the bearings and seals, and make for an unpleasant ride.
3 - 4 % slippage is extremely low, 5% is almost unheard of. Speed read by GPS, or water pressure speedo?
You are over the top of the 4500 - 5500 rpm range so a bit more pitch would be in order. You might want to look a SS with a bit more cup and rake, that would drop the RPM and change how the boat behaves. But it is your boat/motor so it is up to you
 
Last edited:

StingRay_90V4

Petty Officer 2nd Class
Joined
Aug 26, 2014
Messages
155
The speed has been measured for speed accuaracy using my Garmin GPS unit. Surpringly. The factory Speedo is not nearly as in accurate as many people would have you believe. It is out... And its not a linear curve at all. In fact... When I'm doing 20 mph on my Speedo. The GPS says its actually 22 mph. Yet at 30 mph on the Speedo. The GPS says obly 29mph. Yet over 40 mph it is nearly bang on. MAYBE off by 1/2 a mph. I have hit 44.5 mph on the gps. The Speedo said 45 mph. The motor was turning at 5600 ISH rpm. Maybe more like 5550 rpm.
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
12,944
Your water pressure speedo is actually pretty good, close enough for most work.
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
Take a picture of your prop and post it here.

Without seeing a picture of it and going by what you are saying it looks like, I would definitely have this one repaired or replaced. The problem with running a prop that has nicks out of it is that it is now out of balance and can cause issues with your lower unit bearings.
 

StingRay_90V4

Petty Officer 2nd Class
Joined
Aug 26, 2014
Messages
155
No Title

I took this pocture off my dock. So sorry for the odd angle. But if you look closely at it. You can see the peice of the lower blade that is missing. And then the wavieyness of the top blade. I will try to take a better picture over the weekend.
 

Attachments

  • photo272431.jpg
    photo272431.jpg
    185.6 KB · Views: 0

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
Yeah...it's not even a close call...that prop absolutely needs to be repaired.
 

ajgraz

Lieutenant Commander
Joined
Mar 1, 2010
Messages
1,858
I'd get a new prop, and (maybe) keep that one around as an emergency spare.
 

Redfred1

Chief Petty Officer
Joined
Sep 23, 2013
Messages
629
I'm surprised that it doesn't create a vibration when running with it
 

StingRay_90V4

Petty Officer 2nd Class
Joined
Aug 26, 2014
Messages
155
It still hits 43 mph all day with 3 to 4 people in the boat and 44 ish with just myself. Lol... And it somehow only gives 4 to 5 percent slip. I wonder if a new prop would give any less slip. I'm scared to show you guys a straight on shot . šŸ˜Œ
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
12,944
Usually 10% slip is considered good, but sometimes a prop has actually slightly more pitch than advertised and the slip numbers look better
 

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
It doesn't need to be thrown away, just have it fixed, and if you buy another prop use this one as a spare.
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
Usually 10% slip is considered good, but sometimes a prop has actually slightly more pitch than advertised and the slip numbers look better
That's very true. I wonder if the OP really knows what pitch this is.
 

StingRay_90V4

Petty Officer 2nd Class
Joined
Aug 26, 2014
Messages
155
That's very true. I wonder if the OP really knows what pitch this is.

I can only comment on what the prop has stamped on it. I know there is a way to tell the true pitch of the prop. But I don't know how to do that. On the prop otself it is stamped with the brp stock number as well as it picth and diameter. It says it is a 13 1/4 x 17p. And I would have to say that would most likely be the case. i have a 19p omc prop. And the boat doesn't like that prop as much at all. Less omph .
 

Grub54891

Vice Admiral
Joined
Jun 17, 2012
Messages
5,908
Mine is less messed up than that, and I lost 5 mph. Replace or repair.
 
Top