Catastrophic davit crane failure

[SEVEN]

Great point Pascal. On my fly bridge I have about 12 through bolts that go through the core and the ceiling. I’ve added locking acorn nuts to keep it from coming loose. I’m curious why there is missing core in an area that needed the strength.

 

[RonNP]

I think Pascal is right. Through bolts would of been much stronger. The yard is going to add Coos a board where the balsa is missing. There was no water in the bilge but I guess I could have some in the glass of the dinghy but I have not seen any. It’s been dry and hot here lately with no rain

 

[SEVEN]

Ron, mine has a supporting on the top side as well as the inside. Through bolts holding them all together. I’ll send you a photo on Thursday afternoon. I’d suggest you add the interior ring.

 

[SKYCHENEY]

If the winch was free spooling the dinghy back down, did the dinghy hit the water or did the free wheeling abruptly stop? A sudden stop from a lapped/stuck cable or brake on the winch certainly could have imparted enough stress to break something as it caught..

 

[RonNP]

Good question, it happened so fast that I thought the dinghy hit the water and the standpipe snapped at the same time. The dinghy did hit the water but the moment it did the pipe snapped and the crane ripped out of the roof. Perhaps the cable stuck right before the dinghy hit the water. I did have to cut the cable from the bridle as it was tight in the water and the wench wouldn't do anything.

 

[Photolomy]

I would say that the stand pipe failed in the middle due to fatigue, and it then pulled the bottom off the floor plate as the davit/dinghy fell. Did you notice a lot of flex in the middle of the stand pipe during operation before? Is that aluminum or steel?

 

[Pascal]

I had a brain fart yesterday. I looked this morning and the lower flange under the ceiling is smaller and screwed in the ceiling. It s really a piece of trim.

The upper flange though is much bigger, extending about 4” from the stand pipe and the bolts are about 3 1/2” from the stand pipe. When I repaired it a couple of years ago I removed what was left of the balsa core and replaced it with either Coosa or Divinycel epoxied to the skins. Very strong. Before I noticed the flange would be moving when launching. Not good

 

[RonNP]

My pipe was aluminum. I'm leaning towards just replacing the system with a hydraulic davit. The old electric Marquipt davits are a pain to manually push over the dinghy even in calm water.

 

[motoryacht lover]

I second your decision to change to a hydraulic Davit. I had a fully manual electric davit that is much mor problematic to use. Switched to a fully hydraulic unit with dyneema rope and one person launch with ease. I went with a steelhead and am very satisfied. It was 25,000 to install and remove and dispose of old one.

 

[dottieshusband]

Ron, From your description, I'm guessing you suffered a moment of inertia failure. The loaded cable (700lbs?) Freewheeling down, meeting resistance short of the water would have multiplied that 700lbs many times over. Physics is a biatch!