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Old 08-21-2019, 04:50 PM   #1
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That was not planned...

After doing some maintenance and cleaning up our tender, we were lifting it up to put it back on its chocks on the roof of the stern hardtop. Just as it reached the highest point and before we could swing it over, the lifting cable broke and dropped the tender bouncing it off the transom and into the water.

Things we did right: No one was underneath or near the tender. Numerous offers of help before the drop were graciously refused (since we had done this before without help) so there were only the two of us around and out of the way when it fell. Bottom line, no one was hurt.

Things we did wrong: Did not check the dyneema rope under the weight for chafe or rubbing. The rigger had put a knot in the dyneema and the weight rested on that knot. Best I can figure, since the line parted right above the knot, was that the weight had a rough spot and during previous usage had eroded the line. The weight went underwater so there is no chance to verify this. Next time no knot and the weight will clip onto the shackle on the end when needed.

Damage to transom and tender pretty extensive. Awaiting surveyor report and estimates. Will try and upload picture.

Bottom line.... don't stand under a load and never trust anything.
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Old 08-21-2019, 05:01 PM   #2
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Originally Posted by wwestman View Post
After doing some maintenance and cleaning up our tender, we were lifting it up to put it back on its chocks on the roof of the stern hardtop. Just as it reached the highest point and before we could swing it over, the lifting cable broke and dropped the tender bouncing it off the transom and into the water.

Things we did right: No one was underneath or near the tender. Numerous offers of help before the drop were graciously refused (since we had done this before without help) so there were only the two of us around and out of the way when it fell. Bottom line, no one was hurt.

Things we did wrong: Did not check the dyneema rope under the weight for chafe or rubbing. The rigger had put a knot in the dyneema and the weight rested on that knot. Best I can figure, since the line parted right above the knot, was that the weight had a rough spot and during previous usage had eroded the line. The weight went underwater so there is no chance to verify this. Next time no knot and the weight will clip onto the shackle on the end when needed.

Damage to transom and tender pretty extensive. Awaiting surveyor report and estimates. Will try and upload picture.

Bottom line.... don't stand under a load and never trust anything.

Glad to hear that only property was damaged- insurance should take care of that.
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Old 08-21-2019, 05:09 PM   #3
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This is a GREAT "Lessons Learned" post. So glad nobody was hurt.
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Old 08-21-2019, 05:12 PM   #4
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You donít think that will buff out??? Seriously I am in the process of making a crane to lift my port engine out of the engine room in order to replace the fuel tank. I will be taking your lesson seriously.
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Old 08-21-2019, 08:28 PM   #5
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That's the first time I've heard about something like that happening. Glad nobody was injured. The damage is why we carry insurance.


Question--how old is the Dyneema rope? I assume you're going to replace it. Will you go with the same rope or replace it with a stainless cable?
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Old 08-21-2019, 09:15 PM   #6
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I “think” that a knot in Dyneema reduces its strength by about half? Can’t remember exactly what my rope guru told me. It is also allergic to chafing.

Good work about the discipline you showed in your crane work - nobody was hurt, the rest is just stuff.
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Old 08-21-2019, 10:49 PM   #7
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Question--how old is the Dyneema rope? I assume you're going to replace it. Will you go with the same rope or replace it with a stainless cable?

The dyneema was less than two years old. My plan is to use the same thing without a knot or or weight integrated with the line. The old weight had a hole in the middle and the line passed through the weight, thus providing a chafe point. We originally had wire and changed to rope when I got tired of fishhooks and having to replace the wire every time I started to bleed. The dyneema is stronger than wire and does not produce fishhooks. As long as it is protected from chafe and abrasion it works great. If it had not passed through the weight or I had checked where the weight rested, none of this would have happened.
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Old 08-21-2019, 10:59 PM   #8
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Not sure I understand how it was rigged. You had a dyneema crane line that ran through a weight with a knot in the dyneema to hold the weight on the line? What attaches the dyneema to the dinghy? Did you have a hook attached to the end of the dyneema? Was it spliced?

If there was a simple overhand knot to hold the weight in place, that will reduce the strength of the dyneema significantly. The 50% guess may be correct. Constant chafe from the weight, as to speculate, could also do it. My crane (Steelhead Marine) has a weight hook designed for dyneema line. As such the line attaches to the hook in such a way as to not seriously weaken the line. Even a good splice with dyneema will have 90-100% of the breaking strength of the line. Another potential weak point comes with any sharp bends in the line. A sharp radius bend will weeken the dyneema by 50%. However, even 3/16 dyneema has a tensile strength of 5,400 lbs so there is a lot leeway there. Upsize to 1/4Ē and your tensile strength is 8,600 lbs.

Dyneema is still the best material for a lifting crane. Stainless wire would be a very poor second choice.

Iím very sorry you had this happen but Iím very glad no one was hurt.
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Old 08-21-2019, 11:27 PM   #9
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Nick Jackson offers Dyneema/Amsteel as an alternative to SS cable on new cranes and will sell the cable to existing owners.

You might contact them for guidance on the Dyneel cable through the weight. nickjacksonco.com

I'm on my second Nick Jackson davit, but same winch and SS cable. I thought about replacing with fiber line but have been happy with the SS. And, I have SS swaging tools but don't know how to splice Dyneel.
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Old 08-22-2019, 01:21 AM   #10
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I am very curious if the knot was the failure or if it was chafing. I was always told never to tie knots in amsteel/dyneema. I just replaced the line in my crane with amsteel. I spliced both ends and used a thimble on the hook end.
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Old 08-22-2019, 08:24 AM   #11
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Wow. That could have been much worse. The transom took a pretty good whack but nothing a good glass guy can't fix and make look new again.
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Old 08-22-2019, 08:50 AM   #12
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Can your davit take wire?
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Old 08-22-2019, 09:04 AM   #13
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Do you know the diameter of the dyneema and the weight it was lifting? That's pretty strong stuff and I plan on using it myself.
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Old 08-22-2019, 09:09 AM   #14
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Menzies question is a good one. SS wire seems the gold standard to me. Whether rope or wire though, rhe line must be properly rigged, begging the questions posed by the good sailor D Hayes.
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Old 08-22-2019, 09:09 AM   #15
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Nick Jackson offers Dyneema/Amsteel as an alternative to SS cable on new cranes and will sell the cable to existing owners.

You might contact them for guidance on the Dyneel cable through the weight. nickjacksonco.com

I'm on my second Nick Jackson davit, but same winch and SS cable. I thought about replacing with fiber line but have been happy with the SS. And, I have SS swaging tools but don't know how to splice Dyneel.
Agreed- we never switched our lifting cable to dyneema/amsteel even though we use that on our tow bridle.
SS cable has been great and easy to maintain and never get hooks in with a little attention - easier to terminate on the drum and make secure connections.
This is after about 20 seasons with lifting and lowering maybe 50 times or more per season.
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Old 08-22-2019, 09:27 AM   #16
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Wow! That's some nasty damage but at least no one was hurt. Insurance should take care of it. Some good lessons learned there.
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Old 08-22-2019, 10:03 AM   #17
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Question--how old is the Dyneema rope? I assume you're going to replace it. Will you go with the same rope or replace it with a stainless cable?

The dyneema was less than two years old. My plan is to use the same thing without a knot or or weight integrated with the line. The old weight had a hole in the middle and the line passed through the weight, thus providing a chafe point. We originally had wire and changed to rope when I got tired of fishhooks and having to replace the wire every time I started to bleed. The dyneema is stronger than wire and does not produce fishhooks. As long as it is protected from chafe and abrasion it works great. If it had not passed through the weight or I had checked where the weight rested, none of this would have happened.

Sorry, I think our posts crossed paths.

Iím still curious as to what hook you had.

Here is is the hook that Steelhead Marine uses on their cranes with 600-1000 lbs capacity. It is the one on my my crane. The Dyneema connects inside the hook and the hook acts as its own weight. I didnít select the crane it was provided by North Pacific to the original owner. However Iíve been very pleased with how it works and there appears to be no chafing at all of the line.

http://www.advantecstore.com/davitsc...eel_12196.html

The hook has a slot on the side that is designed to slide over a tapered plastic piece so it stays put and doesnít swing around when stored. You can get an idea in the product photos. That is a very nice feature.

Having said that, after your experience Iím going to open up the hook and double check the line termination.
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Old 08-22-2019, 10:18 AM   #18
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Glad you are all OK. My understanding is that the synthetic winch lines need to be properly spliced (no knots). They also deteriorate with UV exposure and should be replaced every two years or so.

Not that stainless steel cables are without issues. Last time at the boat I happened to look at our winch drum while the dinghy was down in the water. I did not like what I saw. The cable was running over a loose loop at a lower layer which had started to fray. We had used the davit about 20 times since we bought the boat. You got to check everything.
Next time we go to the boat I'll replace the cable with new stainless steel. Obviously, the previous owner must have released tension on the cable while out which caused it to unravel at the lower drum layer and then raised the dinghy over that mess.
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Old 08-22-2019, 10:24 AM   #19
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Sorry, I think our posts crossed paths.

Iím still curious as to what hook you had.

Here is is the hook that Steelhead Marine uses on their cranes with 600-1000 lbs capacity. It is the one on my my crane. The Dyneema connects inside the hook and the hook acts as its own weight. I didnít select the crane it was provided by North Pacific to the original owner. However Iíve been very pleased with how it works and there appears to be no chafing at all of the line.

The AdvanTec Store: 600-1000lb, Hook Weight Kit, Rectangular Weight, 316L Stainless Steel

The hook has a slot on the side that is designed to slide over a tapered plastic piece so it stays put and doesnít swing around when stored. You can get an idea in the product photos. That is a very nice feature.

Having said that, after your experience Iím going to open up the hook and double check the line termination.
Dave,

How is the Dyneema connected inside the hook?
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Old 08-22-2019, 11:20 AM   #20
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Glad you are all OK. My understanding is that the synthetic winch lines need to be properly spliced (no knots). They also deteriorate with UV exposure and should be replaced every two years or so.

Not that stainless steel cables are without issues. Last time at the boat I happened to look at our winch drum while the dinghy was down in the water. I did not like what I saw. The cable was running over a loose loop at a lower layer which had started to fray. We had used the davit about 20 times since we bought the boat. You got to check everything.
Next time we go to the boat I'll replace the cable with new stainless steel. Obviously, the previous owner must have released tension on the cable while out which caused it to unravel at the lower drum layer and then raised the dinghy over that mess.
I was surprised at how fast that degradation occurs: https://dynamica-ropes.com/wp-conten...SM-Dyneema.pdf

Even the Dyneema mfg is admitting that your line will degrade far too fast to trust it into the second season, and don't even think about trying some other formultion!
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