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Old 11 March 2008, 11:39   #11
Nick Hearne's Avatar
Country: UK - England
Town: Bucks
Boat name: Blue & Ding Dong
Make: Ribeye,SR4 & Bombard
Length: 6m +
Engine: 115,50 & 15Hp Yams
Join Date: Feb 2004
Posts: 3,232
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Old 11 March 2008, 18:39   #12
Country: Australia
Town: Melbourne
Boat name: Duck Tales
Make: Mercury-Quicksilver
Length: 3m +
Engine: 18hp Tohatsu
Join Date: Mar 2008
Posts: 60
thanks prairie tuber,

"Double check the hub prop to make sure it is not spun. This is far and away the most likely problem." - not sure what to look for, is the hub what holds the prop on? how would i distinguish whether it was 'spun'?

i should have mentioned that i have a ply floor, not air deck.


as a newbie i am trying to get as much information out of the older posts as humanely possible, without nagging you experienced guys with things that have been covered a number of times. though many of the threads are just a little short on the info i need personally. i am determined to get my bearings around SIB's, how they work, what impedes their performances, what enhances it, maintenance, outboard basics etc.....

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Old 11 March 2008, 23:19   #13
Country: Canada
Town: British Columbia
Make: Gemini
Length: 4m +
Engine: 40hp 2 str
Join Date: Oct 2003
Posts: 2,151
Most outboard props have a hub mechanism inside of them to protect the drivetrain of the ouboard. This is in place of the sacrificial shear pins that were used on older outboards. The prop hub mechanism involves a splined metal bushing that slides over the prop shaft that is surrounded by a rubber bushing that is tightly wedged between the splined bushing and the propeller housing The concept is that if the prop strikes something solid such as a rock, the hub inside will give way and spin rather than snap the driveshaft or damage the engine.

Once that hub has been spun, it will still have enough 'grip' to cause the prop to turn under low power (so you can limp back to shore), but as you apply more power the hub will start to spin again. The benefit of this system is that you don't have to try to change out shear pins in the middle of choppy water. The disadvantage is replacing the hub mechanism (or whole prop) is a whole lot more expensive than replacing a shear pin. You should be able to find some schematics of this by googling 'outboard propeller hub' or something along those lines.

As for checking if the prop hub is spun, have a look at the prop. If it looks like that rubber bushing has been twisted up, it has been spun. If you're still not sure, take an indelible marker and mark a straight line along the metal bushing outwards to the propeller housing. Take the boat for a test drive, then look at the prop to see if the splined bushing is still aligned with the propeller housing.

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