prop "slip" at hi rpm

[stevieray]

I recently put a 1988 Celebrity 230 - GM 305 with Alpha One back into service after a 2 yr layout (just built a house - long story). The lower unit had some pretty bad corrosion due to SS prop being left on (another long story). Noticed corrosion was worst where the prop butts into the lower gear housing - may have lost 1/8" of metal in spots along that edge. I ground all the oxide down to bare aluminum & repainted the whole unit. Had it serviced for u-joint, bearings & seals & water pump, and installed a brand new aluminum prop so it is mechanically tip-top. Boat gets out of the hole & planes off OK, but at hi RPM I get an intermittent "slipping" feeling doing 30 - 35 mph. RPM change is too small show on the tach, but is enough to notice by feel. Is it possible that the uneven edge at the housing/prop joint is causing some ventilation? Can't really find anything else wrong.

 

[Kevin70]

Re: prop

Re: prop

How uneven are we talking about? Could you post a picture or two? Oh, and welcome to iboats, by the way.

 

[stevieray]

Re: prop

Re: prop

Damn thing's in the drink - can't get any shots right now. I'd say it is about 50% intact (square, sharp edge) and about 50% I had to grind away some - no more than 1/8" of metal gone, but those areas are smoothed out & painted. I'd generally call it a gradual waviness.

 

[Boatin Bob]

Re: prop

Re: prop

How bad was the old prop, could you throw it in to just test and rule out the new prop?

 

[Reel Poor]

Re: prop

Re: prop

If the prop is not extending into the gear housing (or right at it) there will be enough exhaust leaking around there to blow the water away from the prop causing the cavitation your describing. Wrong prop spacers will cause the same problem.

 

[stevieray]

Re: prop

Re: prop

How bad was the old prop, could you throw it in to just test and rule out the new prop?

Old prop was SS 14.5 x19P - it is in excellent shape & I could pop it back on just to compare. New alum prop has same dims as the SS (which I used to replace the alum one that came with the boat - I never really did see a performance difference with the SS - just looked better sitting on my lift!). One other thing I did this season was to paint the boat bottom since I am now keeping it in the water - could THAT be all I'm feeling is a bit of drag??

 

[Cptkid570]

Re: prop

Re: prop

You could have a spun hub.

 

[stevieray]

Re: prop

Re: prop

You could have a spun hub.

That's the first thing I checked for - it is one of the newer Merc props with the replaceable plastic drive sleeve & everything's intact on the whole assy. Then I started scratching my head.

 

[calwldlif]

Re: prop

Re: prop

Hate to say this because it is
really hard to confirm,
Ignition control Modules act like that
when bad/defective.
Get a service manual and rule out
everything else.

If you feel it is prop related then lets go with that
I am no expert and there are strange things but
if your prop bites to plane it is strange it would blowout at
cruise.
If the hub is verified how about the coupler?
You have better knowledge of your boat than I
and if your gut is saying prop go with it.
Good hunting

 

[Reel Poor]

Re: prop

Re: prop

Read this thread.

Strange Problem

 

[calwldlif]

Re: prop

Re: prop

Thanks RP

 

[stevieray]

Re: prop

Re: prop

Wow - that's a relief - I'm not the only one! I have to pull her sometime soon to replace a leaky trim cyl (more corrosion from the layout/neglect period) & I'll rework the gear housing edge back to square & true all around. 99% sure that'll fix her. I'll keep everybody posted with the results. Thanx all.

 

[Purduebarry]

Re: prop

Re: prop

To check for the spun hub or slipage do the following;

Place a mark on the hub and another on the outer part of the prop in-line with the first mark. Make a test run to duplicate the problem, then check the alignment of the marks. If they are still lined up the prop is not spun. If they aren't aligned, it's spun.

Some of the newer sleeve and prop configurations are prone to this type of problem, even new out of the box. I recall Merc's having this problem.

 

[stevieray]

Re: prop

Re: prop

I checked the prop & sleeve pretty darn close when I pulled it apart when I first started troubleshooting. In order for that thing to spin, the plastic sleeve would need to deform enough to either A) spin inside the prop cavity which is essentially a square shape, or B) spin around the separate bronze drive bushing that fits on the prop shaft splines & has 4 square "keys" cast in to mate to the plastic sleeve. Either way, that plastic would have to change shape pretty drastically. I saw absolutely no deformation in any of these parts - I had a new hub kit standing by if needed to install & could easily compare the two - there was no discernable difference. That is what prompted me to rule out the prop physically slipping. If you see any glitch in my reasoning - let me know & I will check it further.

 

[Purduebarry]

Re: prop

Re: prop

I'm not really sure how the slipage occurs, if the hubs not spun then try posting your delima on the props forum. You said brand new prop. Everything the same as before? Perhaps your getting some cavitation or blow-out, are you triming up? If you rule out slipping and mechanicals are good, then it's a fair bet your having a prop issue. Give em a try over there, good information usually!