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Old 24-01-2019, 00:19   #1
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outboard propeller slipage

Anyone had experience with the rubber hub in outboard propellers causing some propeller slippage?

I have a 9.8 hp 2-stroke Parsun outboard and had a couple of times when on the plane in my 11 foot dinghy where the motor suddenly revved up then instantly settled down (the boat and motor jolting when that happened) but then everything went back to normal. I suspect I hit something submerged. For example, out on a slightly flooded river yesterday and the motor hit something just under the surface (I suspect a submerged float and rope) and the propeller slipped for a split second. Then it gripped and all was good.

Seeing as it has happened a couple of times now, I thought I should investigate more deeply than my usual cursory inspection. Did Google search and eventually found that the propeller has a rubber hub which is designed to slip rather than break something like a gear. I guess it was that causing the slippage.

The propeller has some small chips on the leading edge and lost paint. Some rub marks that look like I hit some rope. No other damage I can see but the rubber hub could be damaged and I would not know.

The prop came off easy and checking it out, does not look like there is any obvious problem with the rubber hub.

Can you tell me at what point I need to replace the propeller (rubber hub not separately replaceable)? I don't think the propeller is slipping anytime except when it hits something rather substantial. I don't think it is slipping when accelerating quickly to get up onto the plane.

Do these rubber hubs fail quickly or slowly? Since my hub has had some slippage but seems to keep working fine, does that mean it is okay or does it mean I should replace it? For insurance, should I carry a replacement prop and tools?

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Old 24-01-2019, 01:00   #2
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Re: outboard propeller slipage

if the rubber hub on your propeller is damaged it will progressively get worse quickly. It will not slip and then go back to normal. looking at the back of the impeller. you would see signs of the rubber deteriorated
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Old 24-01-2019, 01:41   #3
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Re: outboard propeller slipage

Time for a new prop. You most likely hit something and the hub did its breakaway job. If you are a distance cruiser you should also have a backup. Small props are pretty cheap. Some places can press in a new hub, but that will be half the price of the prop.
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Old 24-01-2019, 02:54   #4
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Re: outboard propeller slipage

Once the rubber shears, it has done its thing and the prop needs replaced. The advantage of this type of prop, unlike one with a shear pin, is that it allows you to limp back to port.

If you are still able to get on plane consider yourself lucky ... must be a light dinghy. On a powerboat you're usually confined to idling your way home.
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Old 24-01-2019, 03:12   #5
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Re: outboard propeller slipage

Just went thru this, it was slipping the odd time like yours and I kept thinking that well, the prop should be changed soon. Half way back to the boat on a couple of mile run with just myself in the dingy it just suddenly spun out and that was it. Could barely run above idle, good thing it was a nice day with little wind. Could have been in a pickle with a full RIB and a headwind. A friend drove me to the chandlery where I paid a hefty price for a new prop, at Defender mine is about $30.00 so an inexpensive spare. Advice to myself, if it spins once...replace immediately.
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Old 24-01-2019, 04:01   #6
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Re: outboard propeller slipage

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Originally Posted by troppo View Post
Do these rubber hubs fail quickly or slowly? Since my hub has had some slippage but seems to keep working fine, does that mean it is okay or does it mean I should replace it? For insurance, should I carry a replacement prop and tools? troppo
I don't think the insurance will be the slightest bit interested, but carrying an e bay special or one of those plastic ones if you are making any longer journeys or navigating shallow waters would be good. Have a ditch bag, some basic tools, spare spark plug and spanner and split pins or prop nut, emergency stop lanyard etc in a dry bag.

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Old 24-01-2019, 06:26   #7
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Re: outboard propeller slipage

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Originally Posted by Paul L View Post
... Some places can press in a new hub, but that will be half the price of the prop.
There are two different kinds of propeller hub systems, the rubber hub and the exchangeable hub. The release or failure of the rubber hub or drive sleeve is know as a spun hub.

The rubber hub is composed of a splined shaft surrounded by vulcanized rubber. The hub is pressed into the propeller hub cavity using a hydraulic press, funnel, and hub driver. This is not a field serviceable hub system. If you "spin" a hub you must have it professionally replaced.


The second kind of hub system is the exchangeable hub system. Originally invented by Mercury and known as the flo-torq hub system, this hub system has become more common. It is a field serviceable hub system consisting of a specialized thrust washer, a urethane drive sleeve, and a shaft adapter. The urethane drive sleeve replaces the rubber in the pressed in rubber hub system and works on geometry rather than friction.

https://www.solas.com/exec/product.php?cid=98&lg=E
Hub Replacement Instructions
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Old 24-01-2019, 13:42   #8
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outboard propeller slipage

Are you sure it is the prop slipping on the hub? What you describe sounds exactly like a prop cavitating to me.
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Old 24-01-2019, 13:45   #9
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Re: outboard propeller slipage

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Originally Posted by motion30 View Post
if the rubber hub on your propeller is damaged it will progressively get worse quickly. It will not slip and then go back to normal. looking at the back of the impeller. you would see signs of the rubber deteriorated
Okay, looking closely at the prop, I can see where it the rubber hub has pulled away slightly from the edge. I would guess from the rubber losing adhesion with the metal around it and spinning.
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Old 24-01-2019, 13:51   #10
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Re: outboard propeller slipage

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Originally Posted by Pete7 View Post
I don't think the insurance will be the slightest bit interested, but carrying an e bay special or one of those plastic ones if you are making any longer journeys or navigating shallow waters would be good. Have a ditch bag, some basic tools, spare spark plug and spanner and split pins or prop nut, emergency stop lanyard etc in a dry bag.

Pete
By insurance I didn't mean like from a company but just the personal meaning of doing something as a precaution. My use of the word was ambiguous so it was not clear what I was meaning. Certainly a spare prop and tools would be a good thing to carry on long trips. Or any time I go further in the dinghy than I am prepared to row back.
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Old 24-01-2019, 14:22   #11
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Re: outboard propeller slipage

Thank you all for your comments. I'm gunna replace that prop ASAP. And get a spare.

I've had a look at the links by GordMay (thank you) and done other reading. Unsure if my little propeller comes in an aftermarket version with the field replaceable hubs but I'll see if it does. Rather than buy two props (one to replace, one as spare), I could buy one prop with replaceable hub and a spare replaceable hub.

Whatever, I appreciate all your comments and know the old prop has to go.
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Old 24-01-2019, 14:38   #12
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Re: outboard propeller slipage

as a field repair if the prop has spun its hub ,you can drill and tap 3 bolts between each blade into the hub as a temporary repair to stop the hub spinning.
worked for me in the remote N pacific till i got some where to replace the prop,just don't try 4x4 landrover mode when approaching the beach with it
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Old 24-01-2019, 14:39   #13
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Re: outboard propeller slipage

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Originally Posted by GILow View Post
Are you sure it is the prop slipping on the hub? What you describe sounds exactly like a prop cavitating to me.
A prop cavitating because of air around it and a prop slipping due to hub failure are very similar I believe as far as the effect of the prop slipping (like motor revving suddenly and boat slowing down). However, in my case being on flat water and steady on the plane, there was nothing that could be causing air to suddenly get around the prop and make it cavitate.

What I hate about the river I use the dinghy on is any bit of a flood brings heaps of debris down. Some of it floats, like water hyacinth and you can see logs and sticks. However, with the fish finder running, I see lots of stuff under the water and it is not all fish. On occasion my motor has bucked from touching something which was not on the surface but was a reasonable size. Maybe it was a crocodile. Maybe a log not on the surface. Maybe a submerged float on a mooring. Certainly I have hit enough stuff that it could have damaged the rubber hub. (I have also hit a stump or two in shallow water and other stuff which would not have helped the prop.)

So, after checking the prop closely and from what folks are saying I am fully sure I have a spun hub.
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Old 24-01-2019, 14:50   #14
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Re: outboard propeller slipage

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Originally Posted by atoll View Post
as a field repair if the prop has spun its hub ,you can drill and tap 3 bolts between each blade into the hub as a temporary repair to stop the hub spinning.
worked for me in the remote N pacific till i got some where to replace the prop,just don't try 4x4 landrover mode when approaching the beach with it
I repaired one once with some rubber hose that worked out to be just the right size for a very snug fit. Couldnt go full throttle, but at least I could get home.
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Old 24-01-2019, 15:07   #15
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Re: outboard propeller slipage

It could be that the hub is spun, or it could be that you are hitting submerged objects causing the outboard to kick up over the obstruction and then submerge again.

The way to tell is to take the prop off and make a mark on the outer rim of the hub with a center punch, and then make another punch mark on the splined inner hub that aligns with the outer punch mark. Then take the boat out for a high RPM/high load test run. If the hub is slipping, the marks will no longer be aligned when you return from the test run.

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