Prop Slippage? Cavitation? Ventilation?

[phipps]

I posted a question last fall about my prop losing grip when I power up, rather than reopen and old post, I started a new. Here is the old one if you want to read it: http://forums.iboats.com/showthread.php?t=274679

I finally got a trailer this spring and pulled the boat out. Over the 4th of July weekend I marked the prop to check for a spun hub. I do not have a spun hub, unless I'm really unlucky and it keeps stopping on the same mark. LOL

I'm not sure where to go from here. I will attach a picture of my motor set-up, mayne you have some suggestions.

My motor is not mounted all the way down on the transom, see pic. Would lowering it help me? Is there any downfalls to lowering it?

 

[marlboro180]

Re: Prop Slippage? Cavitation? Ventilation?

Check this out:

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http://www.iboats.com/ref/shaft_length.html

 

[hwsiii]

Re: Prop Slippage? Cavitation? Ventilation?

Phipps, it appears that your motor is in the middle pin as far as tilting it forward or backward, like a trim motor would do. Try moving it forward one more slot so the bottom of the motor is tucked up under the boat more and if that helps you may try moving the pin all the way in, but that may be too much and probably is. If that doesn't take care of the problem I have a form I will want you fill out with information about the boat and motor, and we will do our best to fix your problem.


H

 

[phipps]

Re: Prop Slippage? Cavitation? Ventilation?

Phipps, it appears that your motor is in the middle pin as far as tilting it forward or backward, like a trim motor would do.
H

That's exactly where it is. I got our new bimini put on yesterday and hopefully can get it back up to the lake on Monday or Tuesday. I'll try trimming the motor in and see what happens.



Gary

 

[phipps]

Re: Prop Slippage? Cavitation? Ventilation?

Check this out:

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http://www.iboats.com/ref/shaft_length.html

If I go by that, my motor is way too deep. If I set my motor like the picture has it, the prop would barely be under water. The bottom of my transom just touches the surface of the water.

 

[phipps]

Re: Prop Slippage? Cavitation? Ventilation?

Phipps, it appears that your motor is in the middle pin as far as tilting it forward or backward, like a trim motor would do. Try moving it forward one more slot so the bottom of the motor is tucked up under the boat more and if that helps you may try moving the pin all the way in, but that may be too much and probably is. If that doesn't take care of the problem I have a form I will want you fill out with information about the boat and motor, and we will do our best to fix your problem.


H

Well, I put the boat back on the lake this past week and I tried trimming the motor down and it only "lost grip" one time and we had a bigger load than normal on the boat. I did not get a chance to do much more testing, but it seems it worked.

Thanks!!!



Gary

 

[hwsiii]

Re: Prop Slippage? Cavitation? Ventilation?

I am glad that helped, but I am sure it didn't cure the problem Phipps. Lower the motor down on the transom about another 1 1/2" and I think the problem will be cured.


H

 

[phipps]

Re: Prop Slippage? Cavitation? Ventilation?

Thanks again. Just so happens that the motor is raised about 1 1/2in above the lowest setting. Ill give that a try.

 

[hwsiii]

Re: Prop Slippage? Cavitation? Ventilation?

I think that will take care of your problem completely.


H

 

[dgncsk]

Re: Prop Slippage? Cavitation? Ventilation?

My first message here. Hello to everbody. I am seeking a solution to my problem with 2 stroke johnson 15hp.

Boat is small. it is 5 meter fiberglass. johnson is short shaft type outboard. 1998 make. Propeller is 9x11 (written on one of fins)

Problem is, acceleration and midrange speed/pull is ok. Assume that i am sitting at back and nobody is on board.
When i try to open throttle, it accelerates to a level, it cruises well at 4/3 of throttle.( nose is higher than lower speeds)
When somebody is sitting in front of boat, nose is leveled and there is still acceleration and speed.

Whatever the condition is, on sea surface or load level, when i do full throtlle, nothing happens but engine noise gets little higher. no change on speed.( like climbing on a hill with automatic transmission equipped SUV with a heavy trailer at back)

What can be the cause?

Engine has 5 trim points. It installed at 2nd from bottom.

 

[steelespike]

Re: Prop Slippage? Cavitation? Ventilation?

Welcome,You shouldn't drag up an old thread.There is a thread starter tab at the top of the prop forum.
Take the prop off and draw a water proof line across the hub. do a test run and check the line.
If the line is broken you have a spun hub and the most cost effective solution is to replace the prop.
If your in turkey it may be your only solution.Let us know what you find with a new thread.