Wobbly prop?

[Goodtimegirl]

We have a Volvo 2020 with saildrive and two bladed folding prop. The prop has developed a wobble - feeling like it is loose on the splined shaft. It looks as if the options are new prop or new sail drive - both pretty expensive. Any thoughts on what the culprit might be and possible solutions are welcome.

 

[davidwf]

I think you'll find the prop has a splined tube set inside a rubber bush, the bush is there to absob any shock loads being transmitted from prop to gearbox. Don't know why a saildrive has this bush and a shaft drive dosn't, suspect on a shaft drive the woodruff key will give and the prop spin on the shaft under extreame loads. As the saildrive is splined that cannot happen hence rubber bush.

<font color="red"> </font> The wobbling is probably the bush coming loose. I don't know if its possible to get the bush replaced or not but that's where I'd start looking. Just had a look on the Volvo Penta site and the bush's are replaceable. Quote below from site

Replaceable reinforced bushings are the latest example of Volvo Penta product development in propeller technology. The replaceable bushings are manufactured of high-tech rubber material with extremely high elasticity. The bushing absorbs the shock load that occurs should the propeller leave the water at speed, with rapid forward/reverse manoeuvring or when the vessel runs aground. The bushing gives a certain intentional 'slip' under heavy load without any reduction in the grip of the ...

Rummage about in http://accessorycatalogue.penta.volvo.se/catalogue.asp

 

[Sailfree]

Had this on a charter boat. If it is the Volvo folding prop it lasted approx 500 to 600 hrs, possibly OK on a private boat but sometimes less than a year on a charter boat. Problems included :-
1. Tooth missing on opening enabling blades to open unevenly.
2. The bush also electrically isolates the prop from the shaft so the prop has its own 3 segment circular anode. Max errosion is at the centre of each anode segment where its bolted with SS screw. Bolt hole leaves smaller cross sectional area + corrosion and the anode segments fly off leaving prop unbalanced until all have flown!
3. The splines of the prop appear an aluminium alloy while the shaft is SS. Possibly agrevated by being out of balanced when anode segments fly off the prop splines wear letting prop occilate further agrevating the out of balance.

Life may be maximised by replacing segment anodes before they fly off (every 4 months in the Hamble). If you let it get worse you finally need a new shaft and possibly the shaft bearing.

I finally gave up and changed prop on the charter boat.

Hope this helps.

Roger