shaft breaks at key,

[hubris 1]

pulled the boat yesterday. 29 blackfin with 3126 cats, alright its not a bertram but were cousins. right? pulled out of the slip forward....starboard reverse.....round the corner forward both.....port reverse, clink. off goes the wheel. shafts maybe 9 years old 1 1/2.broke about 2 inches after strut. a total twist. a little spot of darker metal. normal? i havent hit anything. any thoughts. thanks,

[CaptPatrick]

Hub,

If the shaft material is standard stainless, (not Aquamet 19, 22, or equivelent), you pretty much reached, or exceeded, the normal life expectancy...

Recommend that you replace both shafts & shift over to AQ22. Also see: High performance shafting and installation

Br,

Patrick

[Brewster Minton]

Make sure you grind the new shafts keyway to keep that from happening again maybe

[hubris 1]

thanks, i'm going to print that.

[Harry Babb]

Age and alloys are both big factors. This past summer I looked at a shaft out of a Cabo that was less than a year old and it was also broken right at the key on the prop end.

The shafts were Aquamet 22...........came in the boat. Whoever makes the shafts for Cabo does a really nice job.........radiused keyways, clean machine work etc.

My customer asked for my opinion as to why the shaft was broken. Having only the shaft and not the prop and other piece of the shaft is like not having all of the pieces of the puzzle.

I was reluctant to say but I had to think at the propeller was incorrectly installed at the marina when the boat was new. The shaft material did not show any flaws at the fractured area. The broken surface was very smooth and about 25% of the broken surface was discolored and the remaining area was a shiny metalic color. The smooth surface is a sign of fatigue fracture as opposed to a rough grainy fracture the result an accident (High energy fracture) Its my opinion that this is the result of the propeller not seating correctly on the shaft taper and possibly being "Key Bound"

When you install the prop on your new shaft shine a flashlight into the keyway from one end, look thru the other end of the prop and make sure that there is a slight amount of clearance between the top of the key and the keyway in the propeller. Make sure that the key slides freely in the propeller keyway before installation. After the prop has seated on the shaft taper you should be able to use a punch or welding rod to stick into the keyway and actually bump the key back and forth. Then you know that the prop is not keybound.


Harry

[Carl]

Hubris 1,

Guess that was your boat in Cape May Marina? I was looking at it Saturday after we got hauled Saturday afternoon. Pretty boat.

If I knew it was yours I'd have taken a closer look. As was said by Harry, wheel could have been put on wrong, could have been out. Also, if the shaft was bent it would cause shaft to fatigue. Improper key machining can also be a culprit, as mentioned. That is the usual place I see them snap and it would be hard to tell what the exact reason was unless you can come up with the wheel and shaft stub.

Carl

[hubris 1]

sim, sorry i missed you. i pulled the boat on friday, hung around with billy for a while then went home.if i would have known the navigation advise i gave you would bring you to the marina that i dock i would have followed the proper protocol....and bought you lunch at the lobster house. if you do that trip again, i owe you. thanks for the comments on my boat. i do love her! the diver will find the wheel and hopefully the shaft will still be a part of it. just re-powered her with 3126 cats. sometimes, i just go over and sit on her......and listen to her complaints. so far, she has none. but she sure can cost me. ps, dont tell anyone its a blackfin 29, not a bertram! were just cousins.

[Carl]

Hubris 1,
Again, no problem. Your advice did not run us aground, you never said to stay to the right side when entering the Canal. You owe nothing, but if I come down that way again you can offer me a Cold One and we will call it even. Then we can go have lunch at the Lobster House.

As far as going to Cape May Marina, we where going there anyway. My buddy Mark is friends with Billy and his family, so we planned to lay over there for the night. I just met him that day, real nice guy, he called the Tow for us, waited for us to come in, gave us a haul, found us a place to stay in town, made two trips to bring us all to the Condo/Hotel, as we where 5 guys in total. He did all this after hours, when he had plans to be elsewhere. When you see Billy again please tell him we said thanks again, that would be from the crew of Mark and Jo's new boat from Staten Island, I know Mark called and spoke to him since.

You should be able to tell quite abit from that wheel, hope you find it.

I came fairly close to buying a 32 Blackfin with 3208's several years ago. I got the price where I needed it to be, wife really liked it, I had someone interested in my 31 all seemed like a go. But the boat had a vibration and when I started to inquire about the boat further it seemed lots of people knew the boats history. It was bought and sold three times in a relatively short period of time as each guy thought they could get the vibration resolved. They had Caterpiller come down, checked and replaced the running gear, mounts, backing plates and still had that vibration. I passed on it, anyway yeah they are close cousins.

Carl