Prop Shaft Failure

[tomj]

We wanted to spend some money in NC!

[Maine Sail]

Originally Posted by tomj

Recently were heading 'south' in our 1975 Alberg 37 yawl (which we've owned since 1982) when we encountered a broken prop shaft (broke inside the coupling). See the following article (This is the saga of SHEARWATER’s ‘Short Southbound Cruise’) for details. Ideas welcome on what caused the break.....

Have been researching Aquamet shafting (looking at going with Aquament 19) along with Vetus 'Bullflex' couplings. Seems like the Vetus Bullflex series are quite good with good shock absorbing capabilities.

Also looking at R & D Marine Steel Split Half Couplings with the R & D Marine Gearbox Output Flange Adaptor with the R & D Flexible Shaft Coupling in between.

Anyone out there who has went to a Vetus Bullflex coupling, or the R & D setup mentioned above?? Comments and suggestions welcome.

Also, can anyone recommend a Vetus dealer who is willing to correspond with a potential buyer? Have had no luck so far in corresponding with a Vetus dealer.

Thanks,
Tom in Kinsale, VA

Tom,

My .02... You have a flexible coupling (looks like a Federal Flexible Coupling to me) thus a slight misalignment should not have been a huge problem. My suspicion is a poor fit between shaft and coupling that allowed the key & keyway to take the brunt of the load. Eventually fatigue killed it.

Shaft to straight coupling should be an light interference fit which often means cooling / heating to mate the two together. Once together the fit takes a good bit of the load but if sloppy & loose they keyway takes it. The key should also be a snug fit..

My guess is the shaft was at one time removed and the layer of rust that broke free caused a sloppy fit. Could have been a sloppy fit from the get-go too.

[rwidman]

Originally Posted by tomj

We wanted to spend some money in NC!

You don't have to answer if you don't want to, I was just curious. I would have thought a few days for a repair and then continue on your cruise.