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.

wwestman said:

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.

Click to expand...

Glad to hear that only property was damaged- insurance should take care of that.

This is a GREAT "Lessons Learned" post. So glad nobody was hurt.

You don’t 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.

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?

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.

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.

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 1/4” 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.

I’m very sorry you had this happen but I’m very glad no one was hurt.

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.

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.

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.

Can your davit take wire?

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.

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.

syjos said:

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.

Click to expand...

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.

Wow! That's some nasty damage but at least no one was hurt. Insurance should take care of it. Some good lessons learned there.

wwestman said:

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.

Click to expand...

Sorry, I think our posts crossed paths.

I’m 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 didn’t select the crane it was provided by North Pacific to the original owner. However I’ve been very pleased with how it works and there appears to be no chafing at all of the line.

http://www.advantecstore.com/davits...ngular_Weight_316L_Stainless_Steel_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 doesn’t 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 I’m going to open up the hook and double check the line termination.

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.

dhays said:

Sorry, I think our posts crossed paths.

I’m 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 didn’t select the crane it was provided by North Pacific to the original owner. However I’ve 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 doesn’t 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 I’m going to open up the hook and double check the line termination.

Click to expand...

Dave,

How is the Dyneema connected inside the hook?

gsholz said:

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.

Click to expand...

I was surprised at how fast that degradation occurs: https://dynamica-ropes.com/wp-conte...exposure-of-UHMWPE-fiber-from-DSM-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!

syjos said:

Dave,

How is the Dyneema connected inside the hook?

Click to expand...

I'll try and take a photo when I open it up. It will be easier than trying to explain. The dyneema has an eye splice at the end which is trapped inside the hook.

koliver said:

I was surprised at how fast that degradation occurs: https://dynamica-ropes.com/wp-conte...exposure-of-UHMWPE-fiber-from-DSM-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!

Click to expand...

I have always found that the Amsteel we have is very hard to inspect - the ability to tell if it was internal and external fraying, affected by heat, small local kinks make it very hard.
Have had very good results being able to inspect SS line.
The Amsteel we use is in a towing bridle so the affects of heat, UV, cable kinking etc are much more controllable.
YMMV

Oops!

koliver said:

I was surprised at how fast that degradation occurs: https://dynamica-ropes.com/wp-conte...exposure-of-UHMWPE-fiber-from-DSM-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!

Click to expand...

Dyneema will degrade with UV however....


Dyneema has been used for standing rigging in cruising sailboats for quite a while now. The last I heard, the recommendation for a cruising sailboat in the tropics was to replace dyneema rigging every 6-8 years. This is dyneema that is under constant tension out in the sun full time. The recommendation for SS wire rigging is 10 years.


1/4" Amsteel Blue has a tensile strength of 8,600 lbs. 5/16" Amsteel Blue is 13,700 lbs. 1/4" SS 304 wire is around 6,400 lbs.



UV degrades the strength of dyneema. However, the UV affects the outer strands which then act as a UV block to the interior strands. On my crane, the line is protected from UV by the body of the crane as well as a Sunbrella cover. So unlike standing rigging in a sailboat, most crane line is protected from UV rays.


Lets say the dyneema is left out in the sun season after season. If the line strength of the dyneema decreases by 50%, that would mean the strength of that 1/4" Amsteel blue would "only" be 4,300 pounds. My crane is only rated at 600 lbs.



It is obvious that stainless wire works well in cranes on boats despite the issues of corrosion that are well known and prevalent. Dyneema also works well, despite the known issue of chafe and UV exposure. Just as in stainless wire, it is important that dyneema be rigged properly. It isn't hard. It just needs to be done with care.

The caution about knots interests me. A soft shackle made from dyneema utilizes a know as a fundamental part of its operation. Are those knots tied in some special way? It seems they must be?

twistedtree said:

The caution about knots interests me. A soft shackle made from dyneema utilizes a know as a fundamental part of its operation. Are those knots tied in some special way? It seems they must be?

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Yes they are tied carefully and then preloaded so they stay tied. The classic soft shackle tide with a diamond knot when tested to failure will almost always break at the knot. A stronger version of a soft shackle using a modified button knot developed by Brion Toss won't but will usually break at the bend.


Even so, a classic soft shackle will reliably have a strength equal to that of the line it is make from (actually more like 115%) and the stronger version will have a strength of about 230% of the line strength. I just figure 1x and 2x the line strength to make it easy and be conservative.

syjos said:

Dave,

How is the Dyneema connected inside the hook?

Click to expand...

Here is a photo of the insude of the hook. The eye is simply laid over the center portion and the then when the plate is put on the eye can't go anywhere. Also note the diameter of the center post. No sharp bends for the dyneema.

I think it is a great design for a hook on a dyneema line. It came with the boat so I can't claim any credit. My only small complaint is that the length of the bury on the factory splice seems too short.

dhays said:

Here is a photo of the insude of the hook. The eye is simply laid over the center portion and the then when the plate is put on the eye can't go anywhere. Also note the diameter of the center post. No sharp bends for the dyneema.

I think it is a great design for a hook on a dyneema line. It came with the boat so I can't claim any credit. My only small complaint is that the length of the bury on the factory splice seems too short.

Click to expand...

Thanks Dave,

Perhaps incure the bend radius is well past the mimimum....

"3. All end ?ttings should have a minimum 5/1 bending ratio (minimum 80% break strength maintained at 5/1 but break strength drops off fast if the ratio is less):"

Here is the full article...

https://www.sail-worldcruising.com/...eema-lifeline-guidelines/-90520?source=google

smitty477 said:

Perhaps incure the bend radius is well past the mimimum....

"3. All end ?ttings should have a minimum 5/1 bending ratio (minimum 80% break strength maintained at 5/1 but break strength drops off fast if the ratio is less):"

Here is the full article...

https://www.sail-worldcruising.com/...eema-lifeline-guidelines/-90520?source=google

Click to expand...

A bend will reduce the strength of a line. The tighter the radius the more reduction in strength there is. A d/d of 1:1 will reduce the strength of dyneema by about 50%. This is where you get the reduction in strength with a knot of about 65%. This may be where the OPs failure came. However, that alone wouldn’t explain the failure of the line. Assuming the line is 1/4” Amsteel Blue (a common line for this application) it has an average breaking strength of 8,700 lbs and a minimum breaking strength of 7,700 lbs. If the knot reduced the strength by 50%, then that means a minimum breaking strength of over 3,800 lbs. Even with potential shock loads, he wouldn’t have come close to that.

I would point out that if you have an eye splice where the splice goes around another line of the same diameter, that eye splice (if done properly) will still have 90-100% of the strength of the line. The loss is in the splice not the bend. The 1:1 bend weekends the line at the bend by 50%, however in an eye splice you have two lines that are sharing the load. So you have two lines creating 2x the strength, but that is reduced by 50% by the bend, taking you back to 1x.

Having said that, I prefer a larger bend than 1:1 in an eye splice. That is one reason why I like that Steelhead Marine winch hook.