Brass Prop Shaft - Bent and replaced with SS

[Grant Cleverley]

We own a 2001 C320 with 350 hours on the engine. We do not recall hitting anything or getting the prop fouled in crab pots however we just had to replace the prop shaft as it was bent and causing vibration. We noticed brass filings on the floor just ahead of the dripless seal.The boat yard strongly recomended replacing with SS which we did. In their opinion, brass should not have been used on a boat this sizeHas anyone had a similar problem? The repair with engine alignment etc. was around $1K so it was a costly effort.Thanks, Grant

 

[Chris Burti]

BRONZE Prop shaft.

Methinks the yard went fishing and maybe you got hooked. The shaft is bronze...not "brass". Contrary to some popular myths, certain bronze alloys are actually stronger than stainless(not) steel. The shavings are not uncommon in the 320. They often result from curvature of the packing gland tube and are likely from the old packing gland castings...not the shaft. In your case they may have been there prior to the install of the seal. This is one of the (many) reasons that a lot of owners go to the dripless seal. Lastly, a 'bent' shaft doesn't 'vibrate'...it will shake the H@## out of the boat. Mis-alignment of the engine will cause vibration (shaft may even look 'bent' while turning). Misalignment is very common after a haulout. It is well recommended to always do an alignment after a haulout. Failure to do so can result in premature failure of the cutless bearing...same symptoms...fix is 1/3 of the cost of a shaft replacement. Monofilament fishing line can damage a cutless bearing ... again ... vibration, same syptoms as a 'bent' shaft.In your case, an engine alignment should have been done in the water as part of the diagnostic process before pulling the shaft. The cutless bearing should have been checked next,(preferably by diver) If these weren't done by a competent mechanic prior to the final diagnosis... I'd take the old shaft to a machine shup and have it properly checked.

 

[Grant Cleverley]

Thanks Chris

Thanks Chris - Those are very good points. We did have the cutlass bearing replaced first. They we asked them to look at the alignment. He said when they tried to align the engine, they could not get it spot on so they suggested pulling the shaft to be sure.After they pulled the shaft and had it rotated we were told it was bent. I was unaware that the alignment should be done after every haul out. We did have the boat hauled last winter and never thought, or were recomended that it should be aligned. This will save us time and hopefully cash in the future.

 

[Chris Burti]

Curious!

It is a mystery. It takes a pretty good thump to bend a shaft. Glad to hear that they went through the proper steps though.As to haulout alignment, a vessel is designed to be supported uniformly over the entire submerged surface of the hull by the water. When hauled, the only support is by straps and/or jacks. There is, inevitably, some wracking of the hull due to this point loading. This doesn't necessarily mean that the engine shifts every time a vessel is hauled or that after a dozen haulouts, w/o movement, the next haul won't shift the mounts. Prudence dictates either learning how to do it (pretty simple, but can be agravating) or specifying an alignment as part of the launch service after every haulout.Regards

 

[Jim]

So Chris....

I have a C310 and last week I noticed some bronze shaving below the prop shaft in the bilge. Are you saying that this is "normal" and not indicative of a problem or do I have a problem with the packing gland castings?I want to believe that there's nothing wrong.....

 

[Mike]

Knowledge is power

It's good to see someone who thinks before spending a dollar. I can confirm Chris Burti's remark about checking alignment, even after using so called "gentle" Travel lifts. Always check it!