Possible prop slip/hub slip issue? Uncertain how to diagnose

[71satellite]

Hi there,

I have a 1986 Chris Craft 210 Scorpion, with a 350 Mercruiser. Late last fall I made the mistake of thinking the lake had "enough" water, and chewed up my prop (which was a 15" x 19p 3-blade aluminum). At the time, the WOT top speed was approximately 45 MPH at 5000 RPM

I purchased a 15" x 21p prop over the winter, hoping to drop my RPM and increase my top speed.

When I took it out last weekend, the following happened:

-in the water, putting around the dock, all was fine. But the first few times I tried to open the throttle, it seemed like the "clutch was slipping". The motor revved without moving the boat.
-then, oddly enough, it stopped happening (just as I was about to put it back on the trailer, thinking that there was some significant drivetrain issue)
-for the rest of the hour I was on the water, I didn't feel any major slipping, but I noted that at WOT I was down to about 40 MPH, and still revving at 5000 RPM (actually maybe even a bit higher).

Aside from the prop, absolutely nothing has changed. Same weight in the boat, same operating conditions, etc.

I have done some reading online, and am wondering if my prop is slipping on its hub. The prop was "barely used" according to the previous owner, and certainly looked to be in good condition on all surfaces. But I suppose that doesn't mean much.

My question is: Do my symptoms suggest hub slippage? I am planning to mark the prop and hub and take it out again, but the forecast is rain all week so I won't be able to do much for a few days.

I have read some suggestions such as "put the throttle in gear, then try standing on the prop with one foot to see if you can spin it", but I'm a bit nervous about doing damage to the prop/driveshaft. Is that a reasonable test to do?

AND...if you don't think hub slip is my problem, do you have any thoughts on why I'm going slower than I was with a smaller pitch prop? Could there be something about the prop itself?

Looking forward to your reply,
Chris

 

[mommicked]

Re: Possible prop slip/hub slip issue? Uncertain how to diagnose

Did you only change the prop and not the hub.It was probably damaged along w the prop.I believe it could slip and then grab again as described.But Im no expert.

 

[craze1cars]

Re: Possible prop slip/hub slip issue? Uncertain how to diagnose

Could be hub slip. Could also be a failed engine coupler. Same concept, same symptoms, different location of slip.

The coupler is a relatively common I/O failure...but expensive/labor intensive to fix as the engine needs to be removed from the boat.

If you're lucky, you just got a bad hub with your replacement prop. Marking as you indicate with some scratch marks and running again should answer whether the hub is slipping. If it's not, coupler....B.O.A.T....Break Out Another Thousand....

 

[71satellite]

Re: Possible prop slip/hub slip issue? Uncertain how to diagnose

Thanks for your replies. To answer the question - the used prop I purchased came with a hub already installed. I assumed at the time it was in good condition, but I will have to mark and test to ascertain whether the prop hub is the problem or not.

The engine coupler sounds like a nightmare...I've read through a few threads that provide suggestions on how to diagnose, but they are typically related to a complete failure.

If I mark and test the prop hub and it passes, what method can I use to test whether the coupler is the problem. Since the boat is "working" (although going slower than I expect it to), is there a way to test for mild slippage in the coupler (as opposed to complete failure which I assume would be pretty obvious)?

And I hope this doesn't sound naiive, but as I have a jack shaft boat (i.e. mid-mounted engine with a long external driveshaft connecting the engine to the outdrive), do I even have an engine coupler?

Thanks again for your help,
Chris

 

[Bondo]

Re: Possible prop slip/hub slip issue? Uncertain how to diagnose

is there a way to test for mild slippage in the coupler (as opposed to complete failure which I assume would be pretty obvious)?

Ayuh,... Couplers rarely to never go alittle bit Bad,...
It's more of a All, or Nothin'..

Even yer jackshaft affair has a coupler, though not exactly like the 1s used otherwise...

 

[craze1cars]

Re: Possible prop slip/hub slip issue? Uncertain how to diagnose

I'm not familiar with your jackshaft setup. But I'm speculating that with a mid-mount engine maybe you have fairly easy access to actually inspect the output side of the engine where the driveshaft comes out of it?

If yes, then it should be no different than marking your prop hub for slippage...mark the driveshaft and the outer spinning edge of the coupler and go for a ride. If the marks move apart, it has slipped...
And just maybe you have access to replace the couple WITHOUT pulling the entire engine? If that is indeed the failure you are having (might not be)?

Agree in my experience a failed coupler will usually not let a boat move forward much faster than idle speed. Give 'er some gas and the motor just revs and the boat doesn't go any faster...much like you were describing early in this thread. It's really dang obvious.

Why it stopped? Maybe you revved it so fast the heat buildup of the slipping caused the rubber to melt, then cool, and therefore reseal against the splined input metal? I don't even know if that scenario is possible. But if yes, it'll surely be a weak seal, and it will surely fail again....

 

[71satellite]

Re: Possible prop slip/hub slip issue? Water Test Update

Re: Possible prop slip/hub slip issue? Water Test Update

Hello everyone,

Here's the latest info:

I looked at the prop Saturday before taking it out, and I noticed that the "flange" on the prop that seats into the lower unit (to seal and keep exhaust gases from bypassing) wasn't overlapping very much. On inspection, I discovered there was a lot of back and forth play (1/4") on the shaft. Judging by photos I've looked at online I think that I was missing the trust washer! So I took off the lock nut and pulled the prop, and put in a (regular) washer behind it to take out the play. I'll have to buy a proper thrust washer, but I had something lying around that fit so I used it for now.

Then I took the boat out on the water and drove it around. I never felt any slipping (i.e. motor rev up without accelerating), and hit a GPS-verified 43 MPH top speed (with optimal trim) at 4500 RPM (according to the dash tachometer) with wide open throttle.

Interestingly, my MPH stayed the same, but my RPM dropped at WOT! I had read a couple of posts about exhaust blow-by around the propeller if it wasn't seated correctly...I'm wondering if that was happening.


So: where to go from here? The engine coupler seems to be fine, the prop hub didn't slip, my RPM is in the correct range, but my speed seems low considering my prop pitch.
I used a couple of prop slip calculators online, and with the numbers above they calculated 27% slippage. Obviously that isn't good.
With a theoretical 12% slip, the calculators suggest I should be hitting 52 MPH or so.

My boat had only 1/8 a tank of gas, and was not loaded down with junk (just life jackets, fenders, a few tools, and safety gear). I was the only person on board. The hull is absolutely spotless, not a single speck of algae or anything else.

The prop is a "factory" aluminum prop (i.e. no fancy name brands on it), and it does have a slight cupping on the blades.

The outdrive skeg does have a small "shark bite" out of it and some associated burring (caused when the boat hit a rock last fall and demolished the old prop)...I know that I need to clean it up and smooth it out, but I can't imagine that is causing a 10 MPH speed loss.


I'm thinking that I should do a compression test and check all cylinders to ensure they're firing....any other suggestions on what I should look at to try to diagnose the problem?
The motor is running fantastic, very smooth with no hesitation or rough idle/running issues. I suppose I could start looking at tune-up items, and potentially at carb tuning...




Thanks again for your suggestions and advice.

Chris

 

[craze1cars]

Re: Possible prop slip/hub slip issue? Uncertain how to diagnose

So if I'm understanding this correctly, you still do not have a proper thrust washer?

If yes, your generic washer you had laying around may have slowed down the exhaust blow-by from in front of the prop, but you have absolutely no idea if you've eliminated it.

Even the tiniest, smallest little bit of leakage will create a HUGE amount of slip.

I suggest you mount your prop correctly and restest. I still do not believe you have a good baseline at all to make any decisions on. For all we know you may just need a thrust washer, and all your problems will be solved?

To answer your other questions about whether your engine is properly tuned and has good compression...if you don't know the state of any of those condition items for sure, then that tells me it's most certanly time to find out. By all means any old boat stnads to benefit from a comprehensive tuneup and condition check...

If you don't know when any of the following was last done, I suggest all: Plugs (gapped)/rotor/dist cap/wires/timing check & set/carb tune/compression check.

 

[71satellite]

Re: Prop slip issue - replaced prop and things are WORSE!

Re: Prop slip issue - replaced prop and things are WORSE!

Hello again everyone,

Well - first off I have to say I'm a bit embarrassed. Last time I posted I noted that after my test run my prop hadn't slipped.

Well......after finding my "missing" thrust washer (it was stuck to the old prop when I took it off, and I just hadn't noticed), I pulled the prop again to replace it. When I looked REALLLLLLY closely at the mark I had made, I realized that the prop had actually spun 359.5 degrees! What are the odds? Anyways, I noticed that the nail polish mark I had made was cracked, and then when I looked closely I realized that it must have spun all the way around. My dumb luck.

So, feeling that I had finally found my problem, I headed down to the marina to buy a new prop. The shop guy convinced me to go with a Turning Point Hustler prop: it is a 4-blade with asymmetrical blades (two normal blades, two cleaver blades), and a replaceable hub.
The shop guy said these were the "new big thing", giving all the acceleration of a 4-blade, with the top end speed of a three blade. AND a replaceable hub (with a square shape, so no more slipping!).

As described on their website:
"two blades utilize the Hustler high performance variable rake and aggressive pitch design (Blades 2) for incredible hole shot and cornering, and two blades utilize an "offshore" (Blades 1) style shape for high speed and maximum stern lift. This combination results in the highest performance aluminum propeller on the market, unmatched in cornering, acceleration, boat handling, and top speed. This is the ultimate water sports propeller, but also offers any boater four blade performance with none of the usual handicaps of this design"

Sold. I brought it home and bolted it on. This weekend I went out.....and was completely disappointed.

I went from a 15" 21p 3-blade aluminum with a slipping hub: 43 MPH at 4500 RPM

to a 14" 21p 4-blade Hustler prop: 35 MPH at 3200 RPM!!!!

And just for the record:
1986 Mercruiser 350 (260 hp) with Alpha 1 drive in a 21' ChrisCraft Scorpion Jackshaft (approximate weight 3600 lbs plus gear, people and fuel)


I am certainly not an expert in the world of boats, but I simply do not understand what could have happened. Nothing else changed: same weight in boat (okay, 20 gallons more fuel but that's all), same lake and boating conditions.

The motor is running like a top, but I'm heading out (as I type this) to do a compression test. After that, I'm out of ideas.

If blowby was somehow an issue, wouldn't that raise my RPM while slowing me down (because the prop is spinning through more air and less water)?

I checked the gap between the prop "flange" and the lower unit - I couldn't get much more than a playing card in there.


At this point, even far-fetched theories are welcome.

Thanks as always for your help and advice.
Chris

 

[craze1cars]

Re: Possible prop slip/hub slip issue? Uncertain how to diagnose

What is your gear ratio?

"Running like a top" is a rather non-objective statement. So in addition to your compression results, what is your base ignition timing? Is it correct against specs? And have you checked your timing advance against specs? Have you tested all your spark plug wires to make sure they ohm within spec? How old is distributor cap/rotor? Condition? Are your carb butterflies opening all the way when you move throttle lever to WOT? If it's a 4 bbl is your secondary circuit functional? Is the choke releasing fully when warmed up? Do you know for a fact that your tach is accurate? What do your spark plugs look like (lean/rich)?...

I could go on...this could be a whole lot of things other than a prop problem...

Or...your boat may simply have a ridiculously high gear ratio. And therefore it may simply need a lower pitch prop...

I can do nothing but guess based on info provided thusfar...

 

[71satellite]

Re: Possible prop slip/hub slip issue? Uncertain how to diagnose

I pulled all the plugs - everything is a nice light tan colour.

I checked compression on all cylinders - 160 to 175 PSI across the board.

I checked to confirm spark on all wires - everything is igniting.

And yes, butterflies are opening fully at WOT (haven't tested in the water to confirm vacuum secondary opening yet)


I did not check ignition timing or advance; however, the "problem" I feel I'm experiencing is a loss in performance when switching from the old (slipping) prop to the new prop. I was achieving 4500 RPM and 43 MPH with the old (slipping) prop, so I don't think that there is an issue with engine running condition.
Although it often doesn't guarantee anything, the engine was reported to have been rebuilt, with 43 hours on the hour meter, when I purchased the boat from the marina.

Any other thoughts? I plan to put the old prop back on and run it once more to confirm that it performs better, and then unless I can come up with something else to check I think I will have to take the new prop back for an exchange.

 

[craze1cars]

Re: Possible prop slip/hub slip issue? Uncertain how to diagnose

What is your gear ratio?

And I still definitely suggest ignition timing be checked. Just a few degrees off will cost a great amount of horsepower and RPM. There are no guarantees that the engine rebuilder set it to proper specs, as has been proven many times here on Iboats, usually from people who have spent months chasing their tails....

A very recent post as an illustration...
http://forums.iboats.com/showthread.php?t=444839

 

[dragginanchor]

Re: Possible prop slip/hub slip issue? Uncertain how to diagnose

Those Turning point props are very aggressive and really bite into the water compared to an OEM prop. I have 2 of the 3 blade for my boat.
For example, was getting 5600 RPM @ 42 MPH with a omc 14x19 three blade, and 5200 RPM @ 43 MPH with a hustler 13.25x 19, with better hole shot.
Going to a 13.25x 17 improved hole shot further, much better acceleration, and went 5400 RPM @ 43 MPH. BTW Bayliner 1750, 2.3L

I wouldn't be surprised if that new fancy 4 blade is extremely aggressive (alot of bite, less slip), and when going to a 4 blade don't you go down a step in pitch, not up?

 

[mommicked]

Re: Possible prop slip/hub slip issue? Uncertain how to diagnose

Same 21" pitch, extra blade,sounds like you need to try a 19" or 17" pitch 4 blade.but Im no expert.I think the 3 blade prop was slipping in the water not the hub,.......fat,or heavy boat,water in the hull?1986/ w lots of motor/ torque/ prop pitch.But im no expert.

 

[71satellite]

Re: Possible prop slip/hub slip issue? Uncertain how to diagnose

HI again,

Sorry I missed the other question - gear ratio is (assumed to be) 1.5 to 1. Then again, I haven't verified that either.

The shop guy said that the 4-blade hustler, with the same pitch as my previous prop, would perform the same/better because of the asymmetrical blades (i.e. no need to drop pitch).
I could understand a few hundred RPM drop, but over 1000??

Hope to have good weather this week to re-test the old prop and verify whether the Hustler is the issue or not. At the same time I will check ignition timing.

Thanks for your help so far,
Chris

 

[craze1cars]

Re: Possible prop slip/hub slip issue? Uncertain how to diagnose

The shop guy said that the 4-blade hustler, with the same pitch as my previous prop, would perform the same/better because of the asymmetrical blades (i.e. no need to drop pitch).
I could understand a few hundred RPM drop, but over 1000??

Last I checked you said your 21 pitch prop had a slipping hub. Any RPM data from that prop is therefore useless.

So I see no benefit from your plan to go back out and compare the performance your brand new prop with one that is known to have a slipping hub...it will provide no usable data, unless you invest in having the slipping prop re-hubbed first. That might be a good idea, maybe $70-ish?

Or how about taking your original 19 pitch prop to a prop shop and having the chewed blades rebuilt (also usually $70-ish?)

Either of those two props in repaired condition will help you establish a good baseline. Or see if this local marina has some decent used props for you to borrow for a day so you can finally get some good usable data.

My best guess is that if you want a 4 blade, you may need to go down to a 17 pitch prop. That is only a guess, and is based on many, MANY assumptions...

I could very easily be flat wrong. Good luck!

 

[71satellite]

Re: Possible prop slip/hub slip issue? Latest test results

Re: Possible prop slip/hub slip issue? Latest test results

Hello again,

Here are the results of today's tests:

Initial timing is 6 degree advanced.
Total timing (measured at 3500 RPM in neutral) is 30 degrees

Interesting comment - I noticed that my distributor does not have vacuum advance. Perhaps it is because it is electronic ignition...I just found that odd.

I did not measure engine vacuum, as I couldn't find a convenient port to insert my vacuum gauge into.


I also used a diagnostic tachometer and verified that my tach is accurate, and used a GPS to verify speed.

I borrowed a 19 pitch prop (plain-jane mercruiser 3-blade), and hit 43 MPH at 4400 RPM.

Then, without changing enything else, I swapped on the Hustler 4-blade, and with trim adjusted to maximize RPM, I hit 42 MPH at 3800 RPM.


So - I really cannot find any faults with my engine and drive. I am getting better performance (i.e. top end speed) from an old 3-blade 19p prop than a new technology 4-blade 21p prop.

Unless someone has a suggestion, I'm going to return the Hustler and exchange it for a new 3-blade 21p and see what that does. The goal here is to get 50 MPH out of my boat. Everything I've read says it should be possible...


Side note - regarding hub replacement: It is very expensive where I live (southern Ontario Canada)...about $100 to get a hub replaced, which is about what they're selling new 3-blade props for now! Crazy.

 

[Bondo]

Re: Possible prop slip/hub slip issue? Latest test results

Re: Possible prop slip/hub slip issue? Latest test results

Hello again,

Here are the results of today's tests:

Initial timing is 6 degree advanced.
Total timing (measured at 3500 RPM in neutral) is 30 degrees

Interesting comment - I noticed that my distributor does not have vacuum advance. Perhaps it is because it is electronic ignition...I just found that odd.

I did not measure engine vacuum, as I couldn't find a convenient port to insert my vacuum gauge into.


I also used a diagnostic tachometer and verified that my tach is accurate, and used a GPS to verify speed.

I borrowed a 19 pitch prop (plain-jane mercruiser 3-blade), and hit 43 MPH at 4400 RPM.

Then, without changing enything else, I swapped on the Hustler 4-blade, and with trim adjusted to maximize RPM, I hit 42 MPH at 3800 RPM.


So - I really cannot find any faults with my engine and drive. I am getting better performance (i.e. top end speed) from an old 3-blade 19p prop than a new technology 4-blade 21p prop.

Unless someone has a suggestion, I'm going to return the Hustler and exchange it for a new 3-blade 21p and see what that does. The goal here is to get 50 MPH out of my boat. Everything I've read says it should be possible...


Side note - regarding hub replacement: It is very expensive where I live (southern Ontario Canada)...about $100 to get a hub replaced, which is about what they're selling new 3-blade props for now! Crazy.

Ayuh,... Marine motors never use vacuum advance...


You don't have enough Horsepower to spin a 21" prop....
You need a 19" prop...

It'll take ya about Another 100 Horsepower to get it up to 50 mph...

 

[craze1cars]

Re: Possible prop slip/hub slip issue? Uncertain how to diagnose

I have no idea what your motor's timing advance is supposed to be....did you compare your results with your motor's actual specs? Is 6 degrees/30 degrees advaced, retarded, or correct for that model?

Also curious, you posted earlier that you ran 3200 at 35 mph on the 21 pitch Hustler. Yet this time you ran 3800 and 43 mph on the exact same prop. Why? What changed so drastically on your boat between the 2 tests? That's 2 extremely inconsistent results for one prop, and a possible indicator of an intermittent problem.

But anyhow it now seems you have 2 good test results with 2 known good props. Based on those results it seems to me that your plan of exchanging your 21 pitch prop for another 21 pitch prop is a poor plan. 21 had you under-revving. Especially if you get one that is cupped, or a 4 blade...which is the same as adding yet more pitch. When you tested, you got better performance from the plain-jane 19 simply because your motor/boat cannot handle a 21. So by all means do not buy another 21.

As Bondo stated, you need something closer to a 19 pitch prop. Or maybe if you really want that 4 blade "new technology" Hustler (or any other better/cupped/stainless/whatever prop), a 17 pitch may actually be necessary, to allow your motor spin faster and get up into its powerband. "Newer/better" props will bite the water harder (because they have less slip). Therefore they will drag your RPMS down because they work better. To compensate for that, you must to go with lower pitch.

Be aware a lower pitch prop will still be very likely to get you much, if any, more top speed. But you should get similar top speed and improved holeshot.

But there is no question that if you get another 21 pitch prop, you will continue to have low RPMS and will have similar (poor) results.

But the more this goes on and the more you check and report back, the more it sounds to me like you simply do not have a 50 mph boat....likely due to hull design, outdrive placement design, weight, and/or the HP output of your engine.

 

[71satellite]

Prop slip....4 blade ...the latest update - I'm out of ideas

Prop slip....4 blade ...the latest update - I'm out of ideas

It took a while, but I finally got out for one more test.


Oh, and an aside - there seemed to be a discrepancy about the two tests I did with the 21p Hustler....it dawned on me about a week ago that the first test I did (low MPH and low RPM) I actually had a 450 lb fat sac (bag of water) in the cuddy. I'm embarassed (again) to say I completely forgot about it when I was writing out the results of that first test with the 21p prop. The sac has not been in the boat for any test since.


Same boat, same lake, same conditions, same overall weight (me and my girlfriend this time, but only an eighth of a tank of fuel).

I exchanged my Hustler 4-blade 21p prop for the identical-design 19p.

The best I could do was 43 MPH at 4100 RPM.

I really can't understand why the boat won't go faster and/or why the RPMs aren't up. Is the new-generation 4-blade prop really biting so hard that my motor can't turn faster? And if that is the case, why am I not getting any more MPH out of it?

Prop slip calculators suggest about 12% slip based on those numbers...so according to their simple math, I'd be going a lot faster if I got my rpms up higher.

Any suggestions on what I can look at/try/swap/etc. If the answer is that I should drop to a 17p propeller, then tell me. But it seems to me that a boat and engine this size should be fine with a 19p prop. If the answer is that my boat and engine combo will never get to 50 MPH - then I'm shocked. It seems like lots of guys with similar setups (even with bigger boats) running 19p props have no problem getting to 50 MPH or faster. I think the issue is my lack of top-end RPMs, but what can I do to get them up?

Incidentally, no problem with holeshot. Pulling me (200lbs) up on a wakeboard the boat launches out of the water, and is doing 20 MPH in seconds (no, unfortunately I didn't time it). Launching without someone in the water, I get up to 25 MPH in what seems like the blink of an eye.


I've checked everything I can think of engine-wise, and haven't found any problems.
As for the exhaust blow-by (a previous thought I had), the boat came with an exhaust tube instead of the exhaust bellows...but the water was clear enough today that at slightly faster than idle I looked over the swim platform, and it certainly didn't look like exhaust gases were coming from anywhere other than the prop hub. And if there was blow-by, that should cause lots of slipping and higher RPM.

As always, thanks for your help and suggestions.
Chris