broken prop

[1simon]

Hi All,

So , a couple of weeks ago I found out that my 3blade fixed prop had somehow broken off from the inner rubber hub.
I bought a new prop Volvo 3 blade prop and got a diver to fit it . He also removed what was left from the old prop.

See photos of both the new Volvo prop,  the old (  what was left of it,), and the new prop fitted n the saildrive.

Has anybody seen anything like this?  Basically the outer alloy prop ripped off the inner rubber hub.

Also, it got me thinking, I see little protection of the prop by the anode. The anode is fixed to the saildrive ( 120S) and not to the shaft.
Does the prop require another anode? Volvo agent did not mention any need for an anode and it is not shown in Volvo 120S or prop manual.

Welcome any feedback .
Simon

[Yngmar]

The rubber bushing acts as vibration absorber, damper and prevents galvanic corrosion of the propeller, as the propeller is insulated from everything else (if the plastic washer between it and the cone is present).

That's why the propeller doesn't need an anode.

And the rubber bushing also acts as "shear pin", when you hit something big enough to suddenly stop the propeller while motoring, which would otherwise damage the saildrive or gearbox. Which is most likely what happened to yours.

[Symphony]

Not unusual and is often the result of getting a wrap around the prop at some time in the past. The rubber hub serves two purposes. First it acts as a shock absorber so reducing the impact from hitting something with the prop. Second it isolates the aluminium prop from the saildrive itself which is why the prop does not need an anode. The anode on the saildrive itself just protects the drive which does need it because of the mix of metals in its construction. However you can still get corrosion of the prop if the protective coating breaks down, but it usually occurs from the tips of the blades down.

It is possible to fit a new hub, but there is a risk that either the bore has worn or, because it inevitably is a very tight fit, the prop casting cracking. New props are relatively cheap so makes sense to replace it with a new one.

[1simon]

Thanks for the explanation!