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Topic: Is the prop flexing (slipping) too much ?

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Hockey Family Male

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Posted: July 19 2010,10:47 am

Post # 1

Hi all

Was running up and down the river this weekend and I noticed something I hadn't noticed before.

I was running at about 3500 rpm doing around 32mph or so, hit smooth water so gave more throttle and the engine would seem to rev a bit more than usual before speed would pick up and match rpms.

I run a 4 blade alum 14.25 x 19

I've had this prop fixed two times over the years for rock hits. My thought is maybe the blades have weakend and are flexing too much on acceleration ? Is this possible ?

I changed the prop out to my 3 blade alum 14.50 x 19

Didn't get to test it too much because we were done for the day. I did get on it a little on the way back to the ramp and it seemed better, but I did still hear a little rev. Didn't seem to exisive as it did with the 4 blade.

I had a light load in the boat. Just 3 of us.

Thanks for any input, thoughts.

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GoFastRacer Male

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Posted: July 20 2010,5:45 am

Post # 2

Sounds like it's an old prop?????, ears will flex especially aluminum. Did this started right after the last repair or just lately???, if it started right after the repair it's possible they decreased the size a bit repairing it instead of building it up, you would never see it but it's noticeable when used. If it just started lately odds are it's getting tired and should be replaced???...

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Hockey Family Male

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Posted: July 20 2010,9:56 am

Post # 3

Thanks GFR

It's the same prop I've been using since the boat was new.
It's an '06 and has maybe 120 hours.

It's been 2 yrs since last repair. First repair was after my first outing with this boat.

This weekend was the first time I noticed it. I might start looking for a SS prop.

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WATERDOG

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Posted: July 20 2010,10:03 am

Post # 4

If your gear ratio is 1.5 your slip is at 24%. Thats a big number for not a lot of weight. Whats your numbers a WOT?

I had a bit of the same thing in my boat last week but I was carrying about a 1000 lbs more than I usally do so I didn't question it.

"Damn you sure know how to fock things up."-GFR

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Hockey Family Male

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Posted: July 20 2010,3:02 pm

Post # 5

I don't know what ratio I'm running. Think I have that written down at home somewhere.

The numbers I gave in the first post may not be exact. I typically run a few high RPMs to MPH.

I believe at about 60 hrs of use, I hit WOT at about 5300 or 5400 RPM at about 49/50 MPH.

Now that I think of it, it has seemed like I've been running a little higher RPM with less MPH lately.

Hockey Family

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WATERDOG

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Posted: July 20 2010,4:20 pm

Post # 6

Quote (Hockey Family @ July 20 2010,3:02 pm)

I don't know what ratio I'm running. Think I have that written down at home somewhere.

The numbers I gave in the first post may not be exact. I typically run a few high RPMs to MPH.

I believe at about 60 hrs of use, Ã‚Â I hit WOT at about 5300 or 5400 RPM at about 49/50 MPH.

Now that I think of it, Ã‚Â it has seemed like I've been running a little higher RPM with less MPH lately.

Assuming you have a 1:50, At 5350 rpm @ 49.5 mph, you're still at 23%. This along with your 24% at 3500 tells me that the prop has "flexed" to somthing less than a 19 pitch. With even a 10% slippage, your prop is now a 16 pitch. The Prop is history. I run a SS Mirage, 19 pitch, your welcome to try it in Havi if you want.
BTW, if your running 1.38 gears, your slippage will be much worse. Numbers should be printed on your drive.

Edited by WATERDOG on July 20 2010,4:22 pm

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Carrera Elite Male

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Posted: July 20 2010,5:46 pm

Post # 7

One Of The Advantages Of A SS Prop, Is They Don't Flex Much.....Most Stock Low HP Bravo Drives Are 1.5....

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GoFastRacer Male

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Posted: July 21 2010,6:13 am

Post # 8

Quote (Hockey Family @ July 20 2010,4:02 pm)

I don't know what ratio I'm running. Think I have that written down at home somewhere.

The numbers I gave in the first post may not be exact. I typically run a few high RPMs to MPH.

I believe at about 60 hrs of use, Ã‚Â I hit WOT at about 5300 or 5400 RPM at about 49/50 MPH.

Now that I think of it, Ã‚Â it has seemed like I've been running a little higher RPM with less MPH lately.

I'd say it's definitely getting tired, best to replace it before an ear brakes off, that plays hell on the equipment, an SS is the way to go!.. :good

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Hockey Family Male

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Posted: July 21 2010,10:42 am

Post # 9

Thanks all...

I didn't know prop fins get weak over time. That's what it seemed to me, but I wanted to hear from other "knowledgeable" boaters that this could be the case. Wasn't sure if it might be something else.

I did switch it out to my backup prop, which only has a few hours use on it. So that should be good for now until I can afford a SS.
I'm still a little worried about going with SS because I tend to find shallow rocks when they're in the area. :banghead

All the numbers about pitch and rpms and ratios hurt my head. Anyway I found some info last night.

I run Volvo Penta 5.0L GXI SX and I'm pretty sure the gear ratio is 1.60:1
Not 100 % sure. The boat is in AZ so I can't look at the drive.

Hockey Family

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WATERDOG

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Posted: July 21 2010,11:21 am

Post # 10

Quote (Hockey Family @ July 21 2010,10:42 am)

Basic metal fatigue. Those props have 1000 of pounds of pressure on them and they get hot even in the water.
Rocks are a lot worse on alum than steel as alum is weaker and softer.
If the drive is a 1.6, that would knock your slip to 18%, that's still high.

"Damn you sure know how to fock things up."-GFR

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Hockey Family Male

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Posted: July 21 2010,11:48 am

Post # 11

Quote (WATERDOG @ July 21 2010,11:21 am)

Quote (Hockey Family @ July 21 2010,10:42 am)

As far as Rocks and SS.... my concern is the impact on the drive.

Doesn't the weaker alum take away from the force that would be put on the drive gears?
I know hubs are also designed to be sacraficed in a strong impact.
Mostly I'm thinking of low speed hits.

Should I worry about the impact on the drive?

Hockey Family

Can I sue Los Angeles if their boycott reduces my AZ property value?!?
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WATERDOG

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Posted: July 21 2010,12:27 pm

Post # 12

Quote (Hockey Family @ July 21 2010,11:48 am)

Quote (WATERDOG @ July 21 2010,11:21 am)

Quote (Hockey Family @ July 21 2010,10:42 am)

Both the Alum and SS blades have same rubber hub to help with the impacts. Alum would absorb more as it is softer but I don't think your hitting rocks as hard as you might think or your prop would be bent big time already. Just an idea, wouldn't be better to stay away from rocks.

"Damn you sure know how to fock things up."-GFR

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Hockey Family Male

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'06 Monterey 214FS

Posted: July 21 2010,1:51 pm

Post # 13

Quote (WATERDOG @ July 21 2010,12:27 pm)

Just an idea, wouldn't be better to stay away from rocks.

hmmmm....

Hockey Family

Can I sue Los Angeles if their boycott reduces my AZ property value?!?
http://www.azfightsback.com/

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12 replies since July 19 2010,10:47 am

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