Rope around prop shaft - vibration

[boatpoker]

Once witnessed a CS30 approaching the fuel dock, line in water.... caught on prop .... tore shaft strut out of boat. If it had not been so close to the travel lift it would have gone to the bottom. Check your strut.

[Jim Cate]

Originally Posted by Suijin

If you see it wobble on a tabletop then it’s REALLY bent. Even runout you can’t see with your eye can be a problem.

Personally I think it’s easier to have a mechanic take 15 minutes to check it with a micrometer than to go through the trouble of pulling the whole shaft just to roll it on a table lol.

don't want to be nit-picky, but I check runout with a dial indicator, not a micrometer.

Jim

[billknny]

Originally Posted by boatpoker

Once witnessed a CS30 approaching the fuel dock, line in water.... caught on prop .... tore shaft strut out of boat. If it had not been so close to the travel lift it would have gone to the bottom. Check your strut.

Like ^^^^ said!

A tiny bit of a bend in the shaft is a bad thing and should be fixed as soon as convenient. A loose or cracked strut has the potential for immediate disaster.

Have a diver inspect visually, and grab and push/pull form side to side and up and down on the prop. If he feels any movement (there should be none) consider very seriously a haul out before your next sail. It MIGHT be a bad cutlass bearing, but it might be a bad strut too!

[Suijin]

Originally Posted by Jim Cate

don't want to be nit-picky, but I check runout with a dial indicator, not a micrometer.



Jim

Thanks Jim. I don’t own one and did not know what it’s specifically called...I just borrow it asking for “that measuring thing on the flexible arm” lol

[mottseng]

Originally Posted by billknny

Like ^^^^ said!

A tiny bit of a bend in the shaft is a bad thing and should be fixed as soon as convenient. A loose or cracked strut has the potential for immediate disaster.

Have a diver inspect visually, and grab and push/pull form side to side and up and down on the prop. If he feels any movement (there should be none) consider very seriously a haul out before your next sail. It MIGHT be a bad cutlass bearing, but it might be a bad strut too!

Great advise !!! I will do this before heading out again.

[sailah]

Bent shafts can almost always be fixed. See Keith Fenner on YouTube for explanation of how.

https://www.youtube.com/watch?v=MtnkkAzRgP0&t=763s

[Suijin]

Originally Posted by sailah

Bent shafts can almost always be fixed. See Keith Fenner on YouTube for explanation of how.

But usually for near the cost of a new shaft. And then you have a used (and probably scored) straight shaft instead of a brand new one.

He makes it look easy in that video (which is of course why it’s on YT in the first place). It’s not always so easy.

The actual shaft cost is a relatively small part of it. Labor for fixing the skeg, refacing the coupling, installing the new shaft, alignment etc. is going to cost you thousands. Why have someone straighten the old one for $350 when you can have a brand new one made for $500?

[sailah]

Originally Posted by Suijin

But usually for near the cost of a new shaft. And then you have a used (and probably scored) straight shaft instead of a brand new one.

He makes it look easy in that video (which is of course why it’s on YT in the first place). It’s not always so easy.

The actual shaft cost is a relatively small part of it. Labor for fixing the skeg, refacing the coupling, installing the new shaft, alignment etc. is going to cost you thousands. Why have someone straighten the old one for $350 when you can have a brand new one made for $500?

I would respectfully disagree. New shafts are rarely straight, not to the perfection that Keith demands of 0.002" runout. He's a pro I've met him personally and he's done some work for me and friends of mine.

Probably most prominent was a snapped boom on a J40 he fixed the night before the Figawi race. We brought it to him in 2 pieces and went for 2nd place the next day.

Maybe a 1" shaft isn't worth it, but Aquamet rarely wears out. How long did it take him to straighten that? 20 mins?

And on a new shaft you're going to need to fit and face coupling and lap bore of shaft to taper.

Check out some of his other shaft straightening videos when he does a 2.5" shaft. Guy is a pro.

[mottseng]

Looking back I see that I never closed the loop on this one. In the end we had a bent shaft and strut. The shaft got replaced so did the strut and motor mounts. Total cost was around $10K CDN. The biggest job was removing the old strut since it was fibreglassed in and access was not available. An access door had to be cut into the floor of the quarter berth.

[Rob_P]

Originally Posted by Suijin

But usually for near the cost of a new shaft. And then you have a used (and probably scored) straight shaft instead of a brand new one.

He makes it look easy in that video (which is of course why it’s on YT in the first place). It’s not always so easy.

The actual shaft cost is a relatively small part of it. Labor for fixing the skeg, refacing the coupling, installing the new shaft, alignment etc. is going to cost you thousands. Why have someone straighten the old one for $350 when you can have a brand new one made for $500?

For what it's worth, you can straighten a bent shaft yourself on the dock or your table.

2 wooden or metal "V" blocks and an indicator, plus feeler gauges and a C-clamp are all that's required.

The shaft goes into the "V" blocks. The indicator is an arm that goes next to the shaft really close to the surface and stays where it's put. Spin the shaft and measure the gap between it and the indicator with the feeler gauge. You'll know if the shaft is bent by the fact that the gap increases/decreases.

Use the C-clamp to press on the high spot by clamping over the high spot with one end of the clamp and the other end of the clamp under the table. Clamp lightly and measure a lot. All you're doing is bending the shaft back into alignment.

Depending on how lucky or mechanical you are, this could take maybe half an hour to an hour. Setting up and putting the tools away will take longer in most cases than the repair.