Cavitation?

[LateNightSalami]

Hey all!

I have a 2008 VTX 20 with what I believe is an OJ Cinco prop. I experienced something pretty weird yesterday while on the lake. Here is a timeline:

We had parked the boat on a sand beach to swim a bit. When we got back in the boat it was touch to dislodge the boat from the sandy beach initially. I realized that we might be weighing the boat down on the prop so I went around back and lifted and pulled the boat which got it moving easy enough. On our way back I wanted to get home a bit quicker so I revved up and felt a bunch of shuddering. Seaweed has gotten thick lately so I figured it had a bunch stuck on the prop that I would clear off once I got it back on the lift. Well after hoisting the boat up it was clear...which was alarming. Sighing a bit I got back in the boat with my dad to take it out and see how it would behave. Here is where it gets weird: it takes off fine but I notice it is struggling to get above 25 in a straight line. I tried the throttle full open and the engine revs up to 5200 ROM or so but there is no push coming from the prop, like it is slipping or something. It barely gets to 30 mph. I back off and try this one or two more times with the same effect. Finally I slow the boat down and do 2 things: deploy the power wedge and then bring it back up making sure it is at the home position and hop out to check if I had collected seaweed on my second trip out (which is usually through a patch of thick weeds). I felt nothing on the prop. I get back into the boat and give it another go. Like before shoots out of the hole just fine only this time it is behaving normally and before I know it we are at 45 mph or so. I try 4 or 5 more times to recreate the behavior to no avail, it rises out of the water just fine gets up to 45 easy and seems to hold normal skiing speeds (32 or so) just fine. 32 feels kind of slow after you are at full throttle but unless the paddle wheel suddenly broke I don't suspect anything was wrong with that. After my runs were done it seemed to be behaving fine, I smelled nothing in terms of overheating from the transmission or anything (I will check the fluid tonight though). 

Was I having some cavitation? This seems odd since it was when I was going in a straight line (or very lazy turn).

Does random cavitation happen? Maybe something small on the prop that causes it for a bit only to be dislodged when you slow down?

Could the power wedge have somehow dropped a bit and caused some weird behavior? Is there a safety interlock on the wedge where should it become slightly dislodged it will limit speed and power to the prop to prevent damage?

 

Any ideas would be great.

[MadMan]

You could pull the prop and see if the key is still in one piece.

[Woodski]

A bunch of weeds on the prop could cause that issue, cavitation can do it.  If my boat, I would pull the prop and verify the key is still intact as a slipping prop would do that very thing.

Edit - @MadMan hit return before I did, so you could take that 2 people think you should check the key:)

Edited June 18, 2018 by Woodski

[LateNightSalami]

Thanks for the tip. I haven't pulled a prop before but there are probably guides online and I can't imagine it is that complicated.

[blk93jeepzj]

You stated that it has the OJ Cinco (5 blade prop), correct?

I have this same prop as well.  A standard prop puller usually won't work with this prop because of the extra blade and how close they all are.  

1. Remove cotter pin.

2.  Grab a 2x6 or similar and wedge it between the prop and the hull, so that when you go to loosen the prop nut the prop won't spin.

3.  Loosen the prop nut.  Back it most of the way off but leave it on the prop shaft, so that when the prop comes loose it does't fall to the ground.  You can set the board aside.  

4.  Using a small torch (simple as a butane one for sweating copper pipes) heat up the hub of the prop in a couple of spaces in between the props blades.  

5.  Take a hammer and tap/ hit the prop hub from the back side (bow to stern) next to the prop shaft.  Should pop right loose and slide down to the nut (you'll be glad you left the nut on there since the prop is still hot and you won't want to catch it).

6.  Use a wet rag to cool off the prop the rest of the way so you can touch it again. 

7.  Take the prop nut off the rest of the way.  

8.  Remove prop, watch for the key way too.  It should be loose  and fall out.  

Edited June 20, 2018 by blk93jeepzj
grammar

[LateNightSalami]

On 6/18/2018 at 5:12 PM, blk93jeepzj said:

You stated that it has the OJ Cinco (5 blade prop), correct?

I have this same prop as well.  A standard prop pulled usually wont work with this prop because of the extra blade and how close they all are.  

1. Remove cotter pin.

2.  Grab a 2x6 or similar and wedge it between the prop and the hull, so that when you go to loosen the prop nut the prop won't spin.

3.  Loosen the prop nut.  Back it most of the way off but leave it on the prop shaft, so that when the prop comes loose it does't fall to the ground.  You can set the board aside.  

4.  Using a small torch (simple as a butane one for sweating copper pipes) heat up the hub of the prop in a couple of spaces in between the props blades.  

5.  Take a hammer and tap/ hit the prop hub from the back side (bow to stern) next to the prop shaft.  Should pop right loose and slide down to the nut (you'll be glad you left the nut on there since the prop is still hot and you won't want to catch it).

6.  Use a wet rag to cool off the prop the rest of the way so you can touch it again. 

7.  Take the prop nut off the rest of the way.  

8.  Remove prop, watch for the key way too.  It should be loose  and fall out.  

Thank you for the detailed process! Yes it is a 5 blade prop and I am almost certain it is an OJ (I know acme also had a 5 blade back in the day but they don't look as similar as you would think) I will try to do it soon and report back. I imagine getting the prop back on is a similar process? Saw a quick video and it seems with normal use the prop snugs itself on the shaft which is why you need to heat it to get it off but putting it on is just sliding it on and tightening the nut properly. Due to some funky politics concerning the lake associations on my lake it isn't easy to pull my boat out of the water (I can get it in before memorial day and out after labor day but in between is tricky)  but I can get it hoisted high enough to easily get under there and do it. Just hope I don't drop the key. If the key does need replacing due to wear or me dropping it in the lake like an idiot what size do the OJ cinco props use? Or is that more determined by the shaft?

 

[blk93jeepzj]

Back on is pretty straight forward.

1.  Set prop on the prop shaft.

2.  Place and hold key way in place.

3.  Slide prop up shaft over key way.  (make sure key way doesn't slide forward and bind the prop)

4.  Put on nut and tighten to 35 ft lbs iirc.  (need a block of wood again to keep the prop from spinning)

5.  Replace cotter key.  

I've removed mine laying on a tube or large mat so hoisting it up enough to get to it will work.  A second set of hands is helpful to hand you tools.  The key way is standard for the prop shaft size 1.5 inches long and 1/4 by 1/4 inches, brass.  Bakes carries them along with most dealerships should have them on hand as well.  

[MadMan]

1 hour ago, LateNightSalami said:

 Just hope I don't drop the key.

I'd be more concerned about dropping the prop.  But seriously, when I pull a prop, before I actually slide it off the shaft, I rotate it around so the keyway is on top.  This make it easier to install since you won't have to be holding the key in on hand an the prop in the other.

[formulaben]

1 hour ago, blk93jeepzj said:

Back on is pretty straight forward.

1.  Set prop on the prop shaft.

2.  Place and hold key way in place.

3.  Slide prop up shaft over key way.  (make sure key way doesn't slide forward and bind the prop)

4.  Put on nut and tighten to 35 ft lbs iirc.  (need a block of wood again to keep the prop from spinning)

5.  Replace cotter key.  

I've removed mine laying on a tube or large mat so hoisting it up enough to get to it will work.  A second set of hands is helpful to hand you tools.  The key way is standard for the prop shaft size 1.5 inches long and 1/4 by 1/4 inches, brass.  Bakes carries them along with most dealerships should have them on hand as well.  

This is why I first dry fit the prop without the key, then with a pencil make a ring around the forward edge of the prop, then continue with the install.  If the key binds up, you'll know for sure as the prop won't line up with your pencil mark.