Beat up old prop causing over-revving?

[chillin014]

I took my boat (1990 bayliner) out for the first time for a test run to make sure it would perform decently before sinking any money into it, (hence the reason for running a worn out old prop). I read that the motor should be in the manufacturers preferred RPM range at wide open throttle. Well, I could rev much higher than the recommended 5500...I'd say I could squeeze it out past 6k easily and maybe TOUCH 30 mph. It felt like for how hard the motor was working, it wasnt moving the boat accordingly (could be in my head). Holding a motor at WOT makes me feel uneasy.

So my first attempt to cure this was to buy a new prop. I dont have much of a baseline to go off of since regardless of the current props specs it is very worn out and beat. Is my train of thought correct? -That the prop is so beat that its simply not moving enough water and just spinning rather than propelling?

If this is the case I may be very pleased with the performance increase a new prop will get me. My second question is...where do people get props for these motors (1990 50 horse Force)? The options seem VERY limited...I see few on iboats website, and here and there on other websites..

 

[steelespike]

Re: Beat up old prop causing over-revving?

You should read the stickies at the top of the page.Also the prop helps at the top and bottom of the prop store page.
Yes a beatup prop could cause overreving.Prop size should be on the barrel of the prop or perhaps under the prop nut.The only way to find out what prop you need is to test with a good prop in your present size.Get us the
performance specs as outlinded.

 

[chillin014]

Re: Beat up old prop causing over-revving?

thanks. i read the stickies and the prop info at the store.
I found some markings on the front of the prop under the prop nut. It reads "michigan pr 130". Does this tell me anything? thats only 3 numbers...i thought there would be 4 for the diameter and pitch. Okay i have no idea what im talking about.

here is my pityful prop

 

[truckermatt]

Re: Beat up old prop causing over-revving?

I wouldnt use that prop anymore.... even testing with it, you could damage your outdrive.

what kind of motor do you have....

 

[chillin014]

Re: Beat up old prop causing over-revving?

I wouldnt use that prop anymore.... even testing with it, you could damage your outdrive.

what kind of motor do you have....

that bad eh? its a 1990 50 hp force outboard. i went real easy on it when i took it out (first time since ive owned the boat). that is the only "baseline" i have for comparison basis. id hate to buy a new prop one pitch size larger and then be below the efficiency range.

 

[rrhodes]

Re: Beat up old prop causing over-revving?

There are lot's of prop finders out there but you have not really provided enough information for us to help you.

1990 Bayliner (What model, length, Fuel tank size, average amount of people aboard)

 

[chillin014]

Re: Beat up old prop causing over-revving?

There are lot's of prop finders out there but you have not really provided enough information for us to help you.

1990 Bayliner (What model, length, Fuel tank size, average amount of people aboard)

My mistake. It is a 1600 Capri Bowrider almost 17 foot long...fairly small boat. I cant give an average amount of people on board, it will always vary. I cant imagine more than 4 or less than 2 (avg 3?). Maximum of 12 gallons of gas.

those numbers on the prop were insignificant?

I thought maybe there would be a good source for cheap stuff. In the automotive world there is the marked up stuff, and then the places you can go to get the same exact stuff for better prices. I dont want to be a sucker.

 

[hwsiii]

Re: Beat up old prop causing over-revving?

Chillin, I found the boat to weigh 1,250 Pounds with 2 people, gas, beverages and ice 10 gallons of gas I figured the weight at 2,013 pounds. I show that 1990 force to have a 1.62 gear ratio. With these numbers you should be running a 10" pitch aluminum prop at between 29 to 30 MPH.

H

 

[chillin014]

Re: Beat up old prop causing over-revving?

thanks, I will search around for some. Do you by any chance know what my current props specs may be?

 

[hwsiii]

Re: Beat up old prop causing over-revving?

No I couldn't find any information on that prop.

H

 

[slasmith1]

Re: Beat up old prop causing over-revving?

I would have the existing prop rebuilt costs far less than a new prop works just as good and if you still want a new prop you can at least use that 1 to get some baseline numbers.

 

[truckermatt]

Re: Beat up old prop causing over-revving?

I would have the existing prop rebuilt costs far less than a new prop works just as good and if you still want a new prop you can at least use that 1 to get some baseline numbers.

most of the time is is cheaper to repair it, but in my case, my SS prop was a little dinged up and i was going to repair it, but it wouls cost $125 ( cheaper than $350 new.) but i went on eBay and found a exact match SS prop in perfect shape for $56 shipped to my door,

But, since you dont know any of the specs of the prop then i woudnt go buying something that wont work anyway,

 

[chillin014]

Re: Beat up old prop causing over-revving?

I didnt think repairing something like mine was an option. I'm kind of ready to just drop the money on a new prop and be "done" with it assuming I have the right pitch, etc.

i'll probably just buy a 10" pitch prop. I found one for about 120 shipped rather than 140 from the store here. :redface:

i didnt realize when they repair them they weld on new ..."wings" or whatever they are.

 

[bowman316]

Re: Beat up old prop causing over-revving?

I would rather be under propped than over, because if you are over propped it will be nearly impossible to get on plane, and underpropped you just loose a little speed.

 

[chillin014]

Re: Beat up old prop causing over-revving?

i'll start with the 10" pitch then, its as low as I can go anyway.

or do i have it backwards.

 

[hwsiii]

Re: Beat up old prop causing over-revving?

A 10" Pitch prop will work great on your boat.

H

 

[chillin014]

Re: Beat up old prop causing over-revving?

ive been talking to some local prop shop and he said based on those numbers on the prop it was an 11" pitch. hrmm. doesnt really matter since that prop provided little basis for comparison. I can't imagine needing an even larger pitch, right?
I think I'm going to start with a 10" and see where it puts me.

 

[hwsiii]

Re: Beat up old prop causing over-revving?

Give it a try and let us know.

H

 

[chillin014]

Re: Beat up old prop causing over-revving?

Alright. I went ahead and got an 11" pitch in bronze. Its pretty heavy. The boat performs how it "should" now...right at 5500 rpm at full throttle. Unfortunately...the boat is still slow...I still only get it to just under 25 mph. This is with a friend and I (325 lbs)

 

[hwsiii]

Re: Beat up old prop causing over-revving?

Chillin, at that speed you are showing a prop slip of 29%, which is way higher than it should be.

H