Prop spining out

[jbeener1]

Hope im posting this in the right spot if not then i appologize. I have a 14ft flat bottom boat with a 1992 20 hp Johnson motor. The trim plate on the motor while sitting on the trailer is about 2 inches under the boat,the prop is a 10x13 aluminum prop. At WOT the prop want to spin out about every 30 yard. This is with a man sitting on the back bench seat and a man sitting on the middle bench seat,if i move from middle seat to right in front of the back seat the prop does not spin out. The motor is tucked under the boat as far as it will go. Any help would be appreicated..

 

[steelespike]

Re: Prop spining out

Is the prop a standard issue OMC from 92?
I have a feeling a new prop like a solas amita might solve your problem.
It would be good to know your rpm and gps speed.
How is the hole shot?

 

[jbeener1]

Re: Prop spining out

The hole shot is great. Is there a way to tell if its OMC prop? I will get the rpm and gps speed,thanks

 

[Texasmark]

Re: Prop spining out

I really find this amazing. What is amazing about it is how far your AV plate is below the hull. Even with a keel sort of thing at the center of the hull, 2" below is way down there.

Only thing I can think of is that you don't want to tuck it all the way in. Hypothetically (guessing) with the guy in the mid seat and tucked all the way in, the bow is plowing causing the stern to raise up and ventilate.

Before you worry about another prop, set the tilt bar to one notch out from the transom and run it and 2 out and run that. Come back with the answers.

Mark

 

[steelespike]

Re: Prop spining out

Part number on the prop may help.
But thats not the point. If the prop is 20 years old,blades may be kind of primitive,thick with not a lot of technology.
Probably a little dinged up.
The Solas props use "squeezcast"technology,makes blades thinner and stronger.Have a very good reputation.

 

[jbeener1]

Re: Prop spining out

I really find this amazing. What is amazing about it is how far your AV plate is below the hull. Even with a keel sort of thing at the center of the hull, 2" below is way down there.

Only thing I can think of is that you don't want to tuck it all the way in. Hypothetically (guessing) with the guy in the mid seat and tucked all the way in, the bow is plowing causing the stern to raise up and ventilate.

Before you worry about another prop, set the tilt bar to one notch out from the transom and run it and 2 out and run that. Come back with the answers.

Mark

Thank you Mark i will try that hopefully on Thursday after noon and i will let you know. The first time i ran it it was out to the 2nd notch from the boat and it was doing it,thats why i moved it to the 1st notch from boat out. I will try the 3rd notch out. With the boat on plane and the two guys in it the spray from the the side boat is right at the back of the second bench seat. Where do you think the trim plate should be at? Thank you

 

[jbeener1]

Re: Prop spining out

Part number on the prop may help.
But thats not the point. If the prop is 20 years old,blades may be kind of primitive,thick with not a lot of technology.
Probably a little dinged up.
The Solas props use "squeezcast"technology,makes blades thinner and stronger.Have a very good reputation.

The prop is slightly dinged and the edges are pretty thick. Would the part number be on the outside of the prop?? Thanks

 

[Texasmark]

Re: Prop spining out

Assuming 3 seats, spray location OK. With your current problem I wouldn't raise it even though I think it is 2" too low. But raising it will only aggravate the problem. Run the test you said and if it doesn't work, you might consider a new prop. One thing for sure is that a cupped prop will help to prevent this problem. So, whatever brand prop you buy get one that is cupped. Cupping is a slight deformation at the rear of the blade. It is a sharp increase in pitch. That is what makes them bite. If you can't find another brand that has cupping check out Turning Point Hustler. I know they cup their higher hp props. Might decide on a prop (go to the top of this page and select one) and www Turning Point and ask if that part number is cupped.

Mark

 

[steelespike]

Re: Prop spining out

The prop is slightly dinged and the edges are pretty thick. Would the part number be on the outside of the prop?? Thanks

A number may be near the base of the blades or the end of the hub. But you have the size.
I'm thinking the boat may have 4 or 5 keels to strengthen the bottom.These no doubt cause a certain amount of disturbance in front of the prop. Its even possible that 2 "keels" could be in front of the prop or a Keel may be damaged causing even more problems.
I feel a new Turning Point or Solas prop will improve the performance.
Don't get a prop until we evaluate the wot rpm and speed.

 

[jbeener1]

Re: Prop spining out

A number may be near the base of the blades or the end of the hub. But you have the size.
I'm thinking the boat may have 4 or 5 keels to strengthen the bottom.These no doubt cause a certain amount of disturbance in front of the prop. Its even possible that 2 "keels" could be in front of the prop or a Keel may be damaged causing even more problems.
I feel a new Turning Point or Solas prop will improve the performance.
Don't get a prop until we evaluate the wot rpm and speed.

I will find out the RPMs and speed on Thursday.Thanks

 

[jbeener1]

Re: Prop spining out

A number may be near the base of the blades or the end of the hub. But you have the size.
I'm thinking the boat may have 4 or 5 keels to strengthen the bottom.These no doubt cause a certain amount of disturbance in front of the prop. Its even possible that 2 "keels" could be in front of the prop or a Keel may be damaged causing even more problems.
I feel a new Turning Point or Solas prop will improve the performance.
Don't get a prop until we evaluate the wot rpm and speed.

There is one keel right in line with the motor..

 

[jestor68]

Re: Prop spining out

A Solas Amita 4 blade (12 pitch) might help. All the Solas props I've seen/used are cupped.

 

[Texasmark]

Re: Prop spining out

On keel interference on an alum boat: I have an aluminum boat whose bottom is flat for about 1' on either side of the centerline. Then it has 3 ea 1" progressive steps out to the chine making a stepped hull.....pad boat if you will. The boat has a piece of 1" angle alum welded across the center where the two halves of the hull are welded together, making a V sort of keel, which makes for turbulence right in front of the prop, especially in a tight turn. My engine's AV plate is 1 1/2" ABOVE the bottom of the boat, not the "keel" if you will. I am running a 3 blade Ballistic SS prop (13+ x 24P on a 90 hp) which has high rake and is cupped.

Avitar is a picture of the wake. I can be running at WOT, trimmed all the way out, cut the throttle to about 3/4, do an immediate hard turn, hammer the throttle in the middle of the turn and the prop doesn't break loose. The prop does make the difference.

Mark

 

[jbeener1]

Re: Prop spining out

Gentelman i did get to run the boat on Thursday,how ever our tac machine was not. I had been working on building a jack plate for the boat and i did get it on. It set the motor back almost 5 inches and then i raised the motor to where the trim plate was about an inch below the bottom of the boat (not the below the keel). it ran out great with not prop spin out and ran at 23 MPH. This boat is 14ft with a 48 inch floor,the boat is an old Corp of Engineers boat so the aluminum is pretty thick. I then raised the motor up to where trim plate was running just a about 1/4 inch under the water at WOT,speed was 21 MPH but i only got to run it one time that way cause after the one time it started blowing out again,i am going to lower it back down to where it was at when we hot the 23 MPH. I will run it again to check the RPMs cause the prop measured from 4-3/4 to 4-7/8 inches so i will be shopping for a new prop. I will post results as soon as i can. Thanks for yalls help.