Please Explain How Power Slippage Occurs

GJarrett

Member
Oct 3, 2006
649
Tampa, FL
Boat Info
'02 260 Sundancer
Engines
6.2 MPI
I didn't know how else to word the topic..

(Firstly let me explain that I am very mechanically inclined and have done a lot of major DIY work on autos/etc and have a lot of tools, but this is just the third summer of owning an I/O boat so I'm still in a newbie learning curve here.... I hope my question doesn't sound too basic/stupid but we've all gotta begin learning somewhere. I bought a used DA that is now 14 yrs old so I expect some maintenance issues to come up and that's okay.)

I went out for the first splash/shakedown cruise of the year yesterday in prep for the Charleston cruise this weekend. Early last year, once or twice I experienced what I can only describe as a sensation very similar to a slipping clutch in an auto.... the engine would start revving up but the prop speed wouldn't and it felt like there was a loss of power to the prop. I'd back off power a tad then it would re-grab and that would be the end of it. Yesterday this happened once again.

I thought there was a direct mechanical/geared link between the engine and the outdrive; now I wonder if there's some sort of viscous coupling or clutch between the engine and the outdrive. I don't know how else what I think I feel happening those couple of times could happen otherwise.... (unless maybe a slipping prop hub or something)?

Do I have a problem/is this normal, or am I on the last legs of a coupling/clutch that may wear out sometime soon, or is it something as simple as a prop hub? If this IS a problem what tips and tricks will help me diagnose the true source of it and local the exact problem - to find out if its at the engine, or outdrive, or prop, etc.

Lastly, depending on the problem (if it is indeed a problem), is this DIY type stuff or send-it-to-the-dealer type of problem? I helped a guy regear my outdrive last year after the gears grenaded in it and after noticing all of the special tools and junk needed I figured out that outdrive work is something I'll never be doing DIY.

Thanks for any input and help.
 
Gerald

There is really nothing to "slip" in the driveline other than a prop hub. That's what I would suspect your problem is.

Dave
 
I don't know about I/O in particular, but the symptom sounds like prop cavitation. If you are powering up too quickly, the prop just spins up air bubbles until it grabs and then you get going. On an older boat, you might need the props scanned and trued. Otherwise, just go easy on the acceleration.
 
Props are really 2 piece assemblies with a rubber bushing between the spline and the propellor body. When that donut dries out or has hit something significant it will slip as you described. The design is done that way to protect your gear case in case the prop hits something stronger than it is. The hub slips instead of breaking stuff. Most good propshops stock and can replace the bushing by pressing the hub out of the prop.
 
I agree that it sounds like the prop hub. However, what is a liitle odd is that you said it only happened once or twice in the beginning of last season and then was fine for the rest of the season. I have had prop hubs go bad on me twice. Both times, just before getting on plane, the engine would rev up and the prop would just slip away. It didn't get better and it was continous.

I guess it is possible for a prop hub to be intermitently bad, but I would have it fixed regardless.

Depending on the age, condition, material of the prop, it may be worth it to just buy a new prop. The prop shop should be able to advise. If the prop is in good condition, the prop shop can just re-hub....

good luck,
 
Wow thanks for the speedy help guys.... I'll breathe easier now. I've got a spare prop so if that's the problem and it gets worse I'll just swap props to get me home. I was really afraid it could have been something internal ($$$$).

The prop itself could be to blame because I've got a weird one.... when I first bought the boat it was severely underpowered and needed a tuneup (later on I found out it was timed 11 degrees slow!) but at the time I figured it was just because the engine was too small. With five people aboard it wouldn't plane. So I bought one of those ProPulse adjustable composite props so I could change the pitch as needed depending on whether I was boating alone/light or loaded/heavy. I've been satisified with the prop but it may be the source. I've still got the original 17 pitch aluminum prop so I'll keep it in the anchor hatch as a spare justincase.

It only occurs under hard acceleration at low speeds and I had also thought of cavitation.... it could be just that. If RonF and osd9 are right this all probably points to that, since the problem is intermittent.

Thanks again! I'll sleep better tonight..... tomorrow is a big trip and this was really worrying me. Whew.
 
A slipping prop hub would get worse fast, to the point where you would not have gone all of last season without limping home at idle speed one day.

I wonder if you have your drives down all the way when starting off. Depending on the prop shape and particular boat, some boats are more susceptible to this if not trimmed down all the way when you fist get her up on plane. Your description of backing off the throttle and getting a solid lock up is indicative of this behavior.

Try trimming all the way down, and launching hard from a dead stop. If there is no slip, your hubs are fine.
 
Now that I think of it, I believe it did happen with the drive trimmed up.... I had just backed off a beach (I had the trim up to beach it) and don't think I trimmed it back down before hitting the throttle to leave.

I'm learning a lot today :smt001
 
Sprae props are great to have. And on my I/O boats, I could just get into the shallows and put on a snorkel and swap out. However, you also need to have the right size tools and extra nuts and washers to be really "spared".....good luck.... :thumbsup:
 
OK Gerald..........since we helped you out, how about helping me out. Why do I have an intermittent wheel vibration on my Explorer?

(Ooops wrong forum......guess I better ask that on the Explorer Forum. This is an inside joke folks since Gerald is an Off Roader with an Explorer and he knows more about those things than I'll ever know about my boat :wink: )
 
BLATANT hijack! LOL

Yeah post over there and you'll get immediate answers. If you want to continue the hijack here though, let me know what year you have, 2wd, AWD or 4wd, what speeds and conditions it occurs, etc and I'll tell ya :smt001

....or PM me and I'll answer via PM so we don't get banned here for hijackadness :grin:
 

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