My 2002 H356 developed a "knock" about a week ago when I was motoring. It was not a motor knock and I could not figure quite where it was coming from. I asked the maintenance crew at my sailing club to take an underwater look at what was going on. They came back and told me that the screws holding the prop shaft support bracket to the hull had sheared. As the problem was progressive, that seemed strange to me. They said I may have hit something (flotsam), which in the SF Bay would not be unusual. When the boat was pulled we found the bolts in place but the bracket had broken (see attached). There is no evidence of any induced damage, i.e. prop blades are clean and zincs showed no signs of impact. I am lucky the prop did not do a blade dance on the hull but for some reason that looks clean. I find it pretty unusual for an important cast component to fail after 16 months and wonder if any other 356 owners have experienced similar failures.
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Dick McKee
Bob...I don't know if I am looking at the photo
incorrectly, but it looks to me like the blade portion of the mount broke from the base at the hull. It looks like a case of extreme electrolisis. Again I could be looking a the picture incorrectly, but did someone park a new hot boat in your marina with incorrect ground close to you? Do your thru hulls ect look ok?
incorrectly, but it looks to me like the blade portion of the mount broke from the base at the hull. It looks like a case of extreme electrolisis. Again I could be looking a the picture incorrectly, but did someone park a new hot boat in your marina with incorrect ground close to you? Do your thru hulls ect look ok?
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John Livingston
Bent Shaft?
This is just a wild guess, but I wonder if your prop shaft is bent? The reason I ask is that you said that you heard a knock, could the corrosion on the strut combined with the constant movement of a bent, even slightly, shaft have broken the strut then caused the knock?
This is just a wild guess, but I wonder if your prop shaft is bent? The reason I ask is that you said that you heard a knock, could the corrosion on the strut combined with the constant movement of a bent, even slightly, shaft have broken the strut then caused the knock?
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river9150
Agree w/Dick
I agree with Dick it. Check other boats at your marina. I think the problem is with electrolisis. Be safe!
I agree with Dick it. Check other boats at your marina. I think the problem is with electrolisis. Be safe!
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Richard
My 2 cents
The thing I was thinking is, if it was a hot boat situation wouldnt the zincs be affected? they look ok. It seems to be a fatigue type of break like the prop was trailing something off of one blade flexing the bracket. Just until it broke and then slipped off (rope, canvas ??) Is the bracket just balanced in that position?
The thing I was thinking is, if it was a hot boat situation wouldnt the zincs be affected? they look ok. It seems to be a fatigue type of break like the prop was trailing something off of one blade flexing the bracket. Just until it broke and then slipped off (rope, canvas ??) Is the bracket just balanced in that position?
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Darrell
A Possible Explanation
My suggestion is to show the fractured strut to a metallurgist. It is difficult to see the required detail in the photo, but it appears that the strut leading edge area fracture surface is relative flat (typical of a fatigue fracture), progressing about half-way through the strut to where the fracture surface becomes sharp, (typical of an overload failure). It could be that the strut had a manufacturing defect near the leading edge and vibration caused a fatigue crack that grew until the strut could no longer carry the load.
My suggestion is to show the fractured strut to a metallurgist. It is difficult to see the required detail in the photo, but it appears that the strut leading edge area fracture surface is relative flat (typical of a fatigue fracture), progressing about half-way through the strut to where the fracture surface becomes sharp, (typical of an overload failure). It could be that the strut had a manufacturing defect near the leading edge and vibration caused a fatigue crack that grew until the strut could no longer carry the load.
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Colin
You deserved better.
You deserved better than this from such a new boat. It looks from the photograph like this is a steet strut, is that the case? One good thing is that there was no damage to the hull, for what its worth, things could have been much worse.
You deserved better than this from such a new boat. It looks from the photograph like this is a steet strut, is that the case? One good thing is that there was no damage to the hull, for what its worth, things could have been much worse.
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Bob Barter
Causes for Prop Shaft Break
Thought I should respond to all the ideas brought up with regard to this broken bracket. With regard to electrolysis, I see no sign of it anywhere else. As you see the bracket in the picture, it is just balanced there. It turns quite easily around the shaft so the cutless bearing did not fail and cause a seizure of some kind. The attachment point to the hull is through a 4" x 6" plate that is a part of the casting and is held to the hull with 4 screws (no sign of corrosion on those). The plate sits in a recess in the hull so it is hard to see. The good news about that is that replacing the bracket is easy. I am waiting to hear back from the foundry that manufactured the bracket. Because the break happened so near a section change I can very easily imagine a surface crack that propagated over time. I also considered vibration though a) I have not noticed any unusual vibration in the time I have had the boat and b) until just recently (when the bracket was starting to fail) the drip from the stuffing box had been miniscule which would be one sign of undue vibration.... Thanks for all your ideas. If ever there comes a resolution, I will post it then... I certainly agree with Colin that this should not happen to a boat a little over a year old.....
Thought I should respond to all the ideas brought up with regard to this broken bracket. With regard to electrolysis, I see no sign of it anywhere else. As you see the bracket in the picture, it is just balanced there. It turns quite easily around the shaft so the cutless bearing did not fail and cause a seizure of some kind. The attachment point to the hull is through a 4" x 6" plate that is a part of the casting and is held to the hull with 4 screws (no sign of corrosion on those). The plate sits in a recess in the hull so it is hard to see. The good news about that is that replacing the bracket is easy. I am waiting to hear back from the foundry that manufactured the bracket. Because the break happened so near a section change I can very easily imagine a surface crack that propagated over time. I also considered vibration though a) I have not noticed any unusual vibration in the time I have had the boat and b) until just recently (when the bracket was starting to fail) the drip from the stuffing box had been miniscule which would be one sign of undue vibration.... Thanks for all your ideas. If ever there comes a resolution, I will post it then... I certainly agree with Colin that this should not happen to a boat a little over a year old.....
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captain dare
photo
From what I can see of the photo there appears to be an area of the hull behind the prop where all the bottom paint is gone. It may be that something soft(like a rope ) got caught around the shaft. The whipping around knocked off the paint and the severe imbalance could have torqued/stressed the strut to the breaking point.
From what I can see of the photo there appears to be an area of the hull behind the prop where all the bottom paint is gone. It may be that something soft(like a rope ) got caught around the shaft. The whipping around knocked off the paint and the severe imbalance could have torqued/stressed the strut to the breaking point.
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Rob Irvine
Interesting
I find it interesting that the strut looks rusted and has barnacles yet the screw, shaft, and associated nuts are clean. Also the majority of the bottom looks freshly painted.
I find it interesting that the strut looks rusted and has barnacles yet the screw, shaft, and associated nuts are clean. Also the majority of the bottom looks freshly painted.
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Bob Barter
Prop Shaft Break - Further Clarification
The bracket was the only piece that showed any unusual corrosion, which is one of the things that piqued my interest. I am not sure what Captain Dare is seeing in the photo (unless it is the white support pad), but the paint above the prop shows no signs of any wear at all. There is no indication anywhere that anything was wrapped around the prop or the shaft, i.e. no strands of rope or seaweed, no discoloration or wear pattern anywhere.
The bracket was the only piece that showed any unusual corrosion, which is one of the things that piqued my interest. I am not sure what Captain Dare is seeing in the photo (unless it is the white support pad), but the paint above the prop shows no signs of any wear at all. There is no indication anywhere that anything was wrapped around the prop or the shaft, i.e. no strands of rope or seaweed, no discoloration or wear pattern anywhere.
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captain dare
Support pad
Yeah, my fault, from the photo the support pad looks like an area of white gelcoat that's been exposed. Rethinking things, I'd be surprised if you hit something. I've seen my share of heavily bent struts but very seldom a break like yours. I'd put my money on a casting defect possibly compounded by corrosion and vibration.
Yeah, my fault, from the photo the support pad looks like an area of white gelcoat that's been exposed. Rethinking things, I'd be surprised if you hit something. I've seen my share of heavily bent struts but very seldom a break like yours. I'd put my money on a casting defect possibly compounded by corrosion and vibration.
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