how bad does pitting affect prop?

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North
Posts: 265
Joined: Mon Jul 15, 2013 6:29 pm
Location: Nova Scotia

how bad does pitting affect prop?

Postby North » Wed Jan 25, 2017 12:02 pm

As I try to find a better pitch/ cupping/ performance, I am tempted to spend say, $125- 150 on this prop, vs paying to have my current one changed- that way I have a spare... but, how much will that pitting affect performance? And, could a guy power wire brush it well, clean it and use epoxy paste to fill pits and then grind smooth and apply straight epoxy or some type of paint.... would it hold or just come flying off?

pics in link below show the heavy pitting...

http://www.ebay.com/itm/222338092247?_t ... EBIDX%3AIT

I realize a good prop shop can fix alot but that would offset the price too much....

TAB
Posts: 60
Joined: Tue Aug 09, 2016 3:22 pm
Location: OR

Re: how bad does pitting affect prop?

Postby TAB » Wed Jan 25, 2017 3:13 pm

don't. you will chase your tail with performance and vibrations. you are way better off getting a good prop.

North
Posts: 265
Joined: Mon Jul 15, 2013 6:29 pm
Location: Nova Scotia

Re: how bad does pitting affect prop?

Postby North » Wed Jan 25, 2017 4:11 pm

thanks for the input. \i have very little experience with this prop stuff. my current prop has light pitting, very light compared to the one in link.

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kens
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Joined: Wed Nov 12, 2003 5:25 pm
Location: Coastal Georgia

Re: how bad does pitting affect prop?

Postby kens » Wed Jan 25, 2017 6:32 pm

I would pass on that one,
As I remember, you were still turning too much RPM with your prop, correct?
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

North
Posts: 265
Joined: Mon Jul 15, 2013 6:29 pm
Location: Nova Scotia

Re: how bad does pitting affect prop?

Postby North » Wed Jan 25, 2017 7:30 pm

Hi Ken,

yes, about 500 rpm too much, give or take over the max intermittent rating of 2800rpm.

I may just go ahead and get the cupping added and some pitch to the new one,

I reread some of your posts on my excessive slip numbers. I know you recommended cupping only and maybe even less pitch... but, the (highly recommended) prop guy I spoke with, who is about 3 hours away, thought I needed both.

re: slip - wouldn't the fact that I am (potentially) underpropped and therefore don't have enough cupping and pitch to make use of the engine' available power - would this not make excessive slip in itself? I may not be thinking of slip correctly, but it seems to me that if i don't have enough pitch, the engine and prop are turning at 500 rpms more than they "should" to reach a given speed, let's say - I see that as the prop slipping through the water more than it is pushing it....

I have not had time ot work on the boat since hauling... But, I have 4 months or so till launch, so I want to get moving somewhat on a few items, like the prop....

North
Posts: 265
Joined: Mon Jul 15, 2013 6:29 pm
Location: Nova Scotia

Re: how bad does pitting affect prop?

Postby North » Wed Jan 25, 2017 7:31 pm

Hi Ken,

yes, about 500 rpm too much, give or take over the max intermittent rating of 2800rpm.

I may just go ahead and get the cupping added and some pitch to the new one.

I reread some of your posts on my excessive slip numbers. I know you recommended cupping only and maybe even less pitch... but, the (highly recommended) prop guy I spoke with, who is about 3 hours away, thought I needed both.

re: slip - wouldn't the fact that I am (potentially) underpropped and therefore don't have enough cupping and pitch to make use of the engine' available power - would this not make excessive slip in itself? I may not be thinking of slip correctly, but it seems to me that if i don't have enough pitch, the engine and prop are turning at 500 rpms more than they "should" to reach a given speed, let's say - I see that as the prop slipping through the water more than it is pushing it....

I have not had time to work on the boat since hauling... But, I have 4 months or so till launch, so I want to get moving somewhat on a few items, like the prop....

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kens
Posts: 4390
Joined: Wed Nov 12, 2003 5:25 pm
Location: Coastal Georgia

Re: how bad does pitting affect prop?

Postby kens » Thu Jan 26, 2017 3:58 pm

In all my testing of over a dozen different props, on my Double Eagle, this is the common things that I found out:
1. When you increase pitch, you increase slip
2. when you decrease pitch you decrease slip
3. All the so called prop shops say you get 200rpm per inch of pitch. Not so. I'm getting about 120rpm per inch of pitch.
I get about 100rpm per inch of diameter
4. The learned prop shops say that cupping increases pitch about 1". This is not so with my D. Eagle.
5. My boat responds very dramatically with cupping. Cupping responds about 4" pitch or more

Here is a link to the different props I have tried, and the best ones were of the flatter pitch, with a light cupping.
viewtopic.php?f=20&t=4425&hilit=double+eagle

I have found the cheapest prop massaging is cupping, my vote is to massage your current prop with a medium cup, and run it.
This way you only adjust one parameter at a time to see your effects.

If you adjust pitch and cupping at the same time , you don't know which one did the most good. Nor do you know how much your boat responds to the prop guys massaging.
If your current prop is of no cupping right now, my vote is to start with cupping, and try it.
didn't you mention you wanted a slow speed idle for fishing?? You need a flatter pitch to get slow idle, and cupping will come in to effect as speed goes up.
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

North
Posts: 265
Joined: Mon Jul 15, 2013 6:29 pm
Location: Nova Scotia

Re: how bad does pitting affect prop?

Postby North » Fri Jan 27, 2017 8:54 am

Hey Ken,

In general, I agree with you approach to only change one factor, and see what happens, before changing another..

But, specifically for me, there are two reasons why I would consider adding both cupping and pitch at the same time:

1. the prop shop is a 3 hour drive away.. i can ship of course, but if I get into shipping back and forth 2-3 times, I will eat up $100 very quickly on shipping. As well, I can't try the first changes for results until launch in about 3 months, so I wouldn't really want to then have to take the prop off, ship and wait for 1+ weeks to get back before trying supplementary changes.

2. even if cupping give very positive results, and despite your info/ advice on slip and pitch changes- i really feel i need to load my engine significantly more in order to bring the rpms down about 500rpms from the current 3300rpms (100rpms over WOT rating) to the max intermittent rating of 2800 rpms.

This should then allow me to drop back around 2500rpms, which is the max continuous rating, or even 2200rpms, where the max tourque rating is acheived.

North
Posts: 265
Joined: Mon Jul 15, 2013 6:29 pm
Location: Nova Scotia

Re: how bad does pitting affect prop?

Postby North » Sun Jan 29, 2017 4:52 pm

Well. Took off old prop today, still undecided. But, my current prop seems to work well / don't notice vibrations other than a vibration just above idle that I assumed was the 4 cyl diesel. It smooths about above that small rpm range and is smooth all the way to WOT of 2300rpms.

See pics below. I got the current prop cheap so it had that pitting when I bought it. Could that pitting cause above vibration in limited low rpm range?

With current props pitting, I am hesitant to spend money on cupping and repitching. But, best deals on new ones are about 500 bucks US and with our Canadian doller at about 75 cents US, it would be about $750 to get it home with taxes.
That could get me shot! My wife has seen enough hours and cash going into the boat.
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