Snubber sizing for All Chain Ground Tackle

[Delfin]

Originally Posted by CaptainDana

I agree. I prefer to have my have my grab hook suspended over the water so that the weight of the chain works to keep the hook engaged at slack tide. If you could cite a source, I'd like to know more about the grab hook weakness you mentioned. I've read much from various companies selling a better grab hook, etc. but, I have a goodly number of friends who have bet their lives on grab hooks in the logging industry. None have died except one who got flung high into the air by a yarder. Every hook failure I'm aware of or have read about was as a result of using the hook incorrectly and I've never read or heard that a properly sized grab hook is weaker than the chain (besides, in this application it only needs to be stronger than the rope). The only real issue with grab hooks that I've heard of is that it's possible for a hook to weaken the chain if the hook is snatched and it damages a link.

The WLL of the chain hook will match the chain if the metallurgy is the same. However, the load the hook puts on the chain is at a bit of an angle creating bending force, and that weakens the chain. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3430937/. All that said, why one would use a chain hook rather than a stronger than chain soft shackle that can't come off is unclear to me.

[model 10]

I've done some real world testing of climbing rope too. I left one dock line made of climbing rope on the boat one year and it failed in just a couple of months. It broke right in middle. I have another piece of climbing rope in the dinghy engine hoist and it's no good either. The cover and the core get very stiff in the salt enviro.

[Delfin]

Originally Posted by Simi 60

How does the soft shackle attach?
Loop through link and then hard shackle through soft onto thimble of snubber?

That's not simple so I am guessing there is an easier tool free way.

This is my snub line. I happened to have an Ultra rubber snubber, so incorporated it just for giggles, but it isn't necessary with this setup. The thinner gray line is Amsteel/Dyneema, which is stronger than the stretchy octoplait by a factor of two or so. It is also abrasion resistant, so is the part that passes over the bow roller. I incorporated a yacht thimble on the end, and the soft shackle just passes through this, then through a chain link. The soft shackle doesn't bash the hull on retrieval, as can happen with a chain hook, and is stronger than the chain. As noted above, this size octoplait will give me 20% stretch before reaching the WLL of the chain, and then the load is transferred to the chain.

The reduction of force on the vessel with a snub line is gigantic when some stretch is introduced - as I recall, the force is halved with each foot of travel over which the force dissipates, but a resident physicist might correct me on that. In any case, with around 30' of snub line, tens of thousands of pounds of snatch force becomes a tens of hundreds, and that is the whole point of the system.

Bridles help as well, but are generally too short to provide the force load reduction of a longer snub line.

[Delfin]

Originally Posted by thinwater

They do work, but testing has shown they are no better than making the snubber 5 feet longer. Thus, they are very good for dock lines (which can't be longer) but dubious for snubbers, which can easily be longer.

The one use I've found is that the one I incorporated into mine lets me see the degree to which the line is being loaded. Kind of a visual tension gauge, if you will. If it breaks, no penalty. Other than that, pretty pointless for a snubber.

[jen1722terry]

Hello again and a great thread!

We agree with Thinwater that climbing rope is pretty rugged. It comes in a variety of sizes and, in our experience, is pretty resistant to UV. However, we're talking Maine UV, not Florida UV.

Again, our boat is not large (31' Cape Dory with low windage). This size of snubber (8mm) would not work on a much heavier boat with more windage.

Someone asked why put a snubber on a rope rode? A few reasons:

1. Avoid damaging the expensive rode from chafe and excessive heat as it goes though the bow chock in high winds;

2. The snubber (or snubbers, if you're rigging a bridle) should, we think, have somewhat more stretch than the rode, particularly if one sizes it properly and is able to run the snubber from the bow to a stern cleat like we do.

It's also cheap on sale, as 100 meters makes a lot of snubbers.

We've found that using our long snubber makes for a more comfortable ride in rough weather than just using our 90' chain and attached rode.

BTW, we also use climbing rope for spring lines. Makes for easy sleeping on our 2-boat mooring float in Maine.

After a really bad storm, we would probably retire the snubbers. We carry
extras made from our original 100 meter coil.

We note that Thinwater hails from Deale, MD. I used to sail that area on my little Bristol 26 back in the 80s. I kept the boat at Kent Island across the Bay for an entire winter and got lucky - almost no ice. I'd drive down from my home near Philadelphia and sail on nice winter days. Some days it would be just me and the skipjacks. A very special part of the world. My wife keeps bugging me to take our boat down to the Chesapeake in a year or so, going down in late summer and sailing until early December. We may just do that.

Cheers to all of you!

Jenn and Terry

[Simi 60]

Originally Posted by Delfin

The WLL of the chain hook will match the chain if the metallurgy is the same. However, the load the hook puts on the chain is at a bit of an angle creating bending force, and that weakens the chain. .

I can see how a traditional lifting chain hook can load the side or an angle but that victory hook I put up earlier gently cups the entire link and in the direction of load.

. All that said, why one would use a chain hook rather than a stronger than chain soft shackle that can't come off is unclear to me

We haven't had an issue since we started using a decent loop of chain, 12 ft or more of loop.

I also like the ability to retrieve singlehanded from the wheelhouse if we need a quick getaway in bad weather and as the victory hook hits the roller and unhooks itself the other half can be securing stuff that may break in the rough.

[Delfin]

Originally Posted by Simi 60

I can see how a traditional lifting chain hook can load the side or an angle but that victory hook I put up earlier gently cups the entire link and in the direction of load.



We haven't had an issue since we started using a decent loop of chain, 12 ft or more of loop.

I also like the ability to retrieve singlehanded from the wheelhouse if we need a quick getaway in bad weather and as the victory hook hits the roller and unhooks itself the other half can be securing stuff that may break in the rough.

Do you know the WLL of your hook? I agree that design avoids side loading the chain, and I see your point about single handing retrieval from the pilothouse. I have to do that from the deck, at least for quick removal of the soft shackle.

[Simi 60]

Originally Posted by Delfin

Do you know the WLL of your hook? .

No I don't know the WLL and can find no data BUT when we got the boat it had a 1 inch PP (silver rope) snubber and we had one memorable storm with 80+ knot wind gusts .
Horizontal hail smashing into the windows blocked out view of the deck and snubber but the chain never was quite the same again afterwards always developing unexplainable twists leading to an occasional jump off the chain wheel.
While measuring the chain with calipers didn't reveal much I suspect the chain was stretched to some degree due to no stretch in the snubber.

The chain hook showed no sign of anything different so I consider that tested.

We changed the snubber to 3/4 nylon and replaced the chain and all is well again and I would like to think with nylon the loads should be reduced considerably.
We do see it stretch a few inches in sustained 30+ gusts.

[Alan Mighty]

Originally Posted by Simi 60

when we got the boat it had a 1 inch PP (silver rope) snubber

'Silver rope' also called 'silver staple rope' is continuous filament polyethylene (PE), not polypropylene (PP).

I'd guess that 1 inch silver rope would have a breaking strength in the 4 - 5 tonnes range (closer to 5 tonnes than 4) and it should stretch about 50% of its length just before breaking. Stretch in the working load range is about 20%.

I think your decision to change to smaller nylon rope for a snubbing line was a good one.

[thinwater]

Originally Posted by Simi 60

No I don't know the WLL and can find no data BUT when we got the boat it had a 1 inch PP (silver rope) snubber and we had one memorable storm with 80+ knot wind gusts .
Horizontal hail smashing into the windows blocked out view of the deck and snubber but the chain never was quite the same again afterwards always developing unexplainable twists leading to an occasional jump off the chain wheel.
While measuring the chain with calipers didn't reveal much I suspect the chain was stretched to some degree due to no stretch in the snubber.

The chain hook showed no sign of anything different so I consider that tested.

We changed the snubber to 3/4 nylon and replaced the chain and all is well again and I would like to think with nylon the loads should be reduced considerably.
We do see it stretch a few inches in sustained 30+ gusts.

How long is the snubber? It is not just diameter. Like a fishing pole, the flex of the rod and the line must be matched to avoid snapping the line when the fish gets close. The rope must be long enough, since energy absorption is so many ft-pounds / ft, if you think about it. Short snubbers can't absorb meaningful amounts of energy; there simply isn't enough rope volume to safely do the job. although it is counter intuitive, rock climbers know they are safer the more rope is out. What they fear is a fall near the anchor, with not enough rope to stretch.

[Delfin]

Originally Posted by Simi 60

No I don't know the WLL and can find no data BUT when we got the boat it had a 1 inch PP (silver rope) snubber and we had one memorable storm with 80+ knot wind gusts .
Horizontal hail smashing into the windows blocked out view of the deck and snubber but the chain never was quite the same again afterwards always developing unexplainable twists leading to an occasional jump off the chain wheel.
While measuring the chain with calipers didn't reveal much I suspect the chain was stretched to some degree due to no stretch in the snubber.

The chain hook showed no sign of anything different so I consider that tested.

We changed the snubber to 3/4 nylon and replaced the chain and all is well again and I would like to think with nylon the loads should be reduced considerably.
We do see it stretch a few inches in sustained 30+ gusts.

80 knots is getting a bit brisk, I must say.

My snubber is 3/4" as well, and our boats are very similar in weight and apparent windage. If you're going to experience similar conditions again, I have two suggestions. The first is to get your head examined. The second is to perhaps add a starting section of the snubber in Dyneema like mine to reduce concerns about chaffing. As Thinwater suggests, unless a snub line is long enough to provide some decent stretch, it kind of defeats the purpose, so I assume yours is at least 30'.

[thinwater]

Originally Posted by Delfin

... unless a snub line is long enough to provide some decent stretch, it kind of defeats the purpose, so I assume yours is at least 30'.

In fact, reasonably fat snubbers can OK, as long as they are long enough. The difference in force is not that great, so long as the snubber is >30 feet. Short and skinny fail and short and fat don't absorb shock.


I like skinny because the Chesapeake is generally light wind, occasional violent, and often terrible holding ground (super soft mud, like porridge). Skinny means less force on the anchor, which is nearly always the determining factor. But in consistently windy areas with better bottoms a little thicker is smart (will last longer).

[Simi 60]

Originally Posted by Delfin

80 knots is getting a bit brisk, I must say.

Blew planes around at the airport and shipping containers at the port.

My snubber is 3/4" as well, and our boats are very similar in weight and apparent windage. If you're going to experience similar conditions again, I have two suggestions. The first is to get your head examined. The second is to perhaps add a starting section of the snubber in Dyneema like mine to reduce concerns about chaffing. As Thinwater suggests, unless a snub line is long enough to provide some decent stretch, it kind of defeats the purpose, so I assume yours is at least 30'.

We live aboard on the hook, summer storms in the 50knot range are common enough but thankfully the big ones are more every ten years, or so they say.

No, our snubber is 15ft more in an effort to stop crap growing on the rope.
I should get a longer length while ashore today for when a storm approaches.

[Paul L]

Originally Posted by Simi 60

...
No, our snubber is 15ft more in an effort to stop crap growing on the rope.
I should get a longer length while ashore today for when a storm approaches.

We keep two snubbers available. A short one for day to day use that is primarily to keep the chain quite and perhaps some damping from a wake or gust. A long one for when we expect it to get nasty. The unexpected afternoon thunderstorm usually ends up with the short one still in place or at best the long one out short and ready to extend - assuming someone didn't come up and anchor just below me.

[wrwakefield]

Originally Posted by Jim Cate

...

But I still like all chain!

Jim

You are preaching to the choir Jim!

It has been decades since I used a combination rode on a cruising boat main bower. [I'm not counting the 200ft of 'Hail Mary' Dacron octoplait spliced to the end of 360ft of chain on my main bower...]

Cheers! Bill