Hi Andrew, our chain is 5/16" G-4 with a 40 pound Danforth anchor. Unsure about the rest. According to one chain source, it has a working load of 3,900 pounds.
A Short Story About An Anchor Swivel
- Thread starter Terry Cox
- Start date
The 5/15" G-4 chain has a WLL of 3900#. The smallest Mantus swivel (model S1) has a WLL of 3000# and an ultimate strength of 15000# or 5X higher. Does anyone have specs of when cleats with backing plates will pull out of fiberglass? I'm thinking (very dangerous) that a 3000# load on an anchor would be extremely rare. And what are the chances that any anchor would even hold to the bottom at 3000#? Getting off-topic here..... Sorry. A mind is a terrible thing to let run amuck...
I don't know that amuck is the word Rich, I think they are valid questions.
I can only help with one - cleats pulling out of fiberglass. In September 2018, while we were out of the country, Tropical Storm Gordon made a swing near our area. The boat was in its slip at our club, where the basin is VERY small and is almost surrounded (300 degrees of azimuth, open only on the east) by protective tall mangroves, tall trees, or 2 story buildings. I can't quote storm surge or wind velocities for TS Gordon, but the boat weighed about 11,000 pounds.
We had a cleat rip out the port aft quarter. Two additional factors were in play. One, the rectangular backing plate was 3/16" aluminum, not much longer than the distance between the bolts, and not very wide. Second, the cleat was on a vertical surface, not a horizontal one, so the load was in tension, not shear. Our theory is that when the water drained out of the basin and our shallow bay, the boat was left hanging from its cleats, and that one ripped out. It would have had 4 lines on it, run to different pilings. I don't know if that would help or hurt. 11,000 pounds spread over 4 cleats, so something north of around 2750 pounds? I'm not an engineer, so I don't know if that analysis of loads is appropriate.
Interestingly, the mirror image cleat on the starboard side was fine, despite its complete lack of a backing plate. Needless to say, after I made the repair, all four of my cleats got new and improved backing plates.
I can only help with one - cleats pulling out of fiberglass. In September 2018, while we were out of the country, Tropical Storm Gordon made a swing near our area. The boat was in its slip at our club, where the basin is VERY small and is almost surrounded (300 degrees of azimuth, open only on the east) by protective tall mangroves, tall trees, or 2 story buildings. I can't quote storm surge or wind velocities for TS Gordon, but the boat weighed about 11,000 pounds.
We had a cleat rip out the port aft quarter. Two additional factors were in play. One, the rectangular backing plate was 3/16" aluminum, not much longer than the distance between the bolts, and not very wide. Second, the cleat was on a vertical surface, not a horizontal one, so the load was in tension, not shear. Our theory is that when the water drained out of the basin and our shallow bay, the boat was left hanging from its cleats, and that one ripped out. It would have had 4 lines on it, run to different pilings. I don't know if that would help or hurt. 11,000 pounds spread over 4 cleats, so something north of around 2750 pounds? I'm not an engineer, so I don't know if that analysis of loads is appropriate.
Interestingly, the mirror image cleat on the starboard side was fine, despite its complete lack of a backing plate. Needless to say, after I made the repair, all four of my cleats got new and improved backing plates.
Well that is interesting, and in your particular case (vertical cleat, sub-standard backing plate) having one cleat rip out is understandable. I wonder if this is a typical load for cleat failure or perhaps a low figure.
In any event, if you were anchoring (the original posting was about swivels on an anchor chain) is it even possible to achieve anchor holding in excess of 3000#? If the answer is NO, then a chain and swivel with WLL's of 3900# and 3000# respectively is no risk at all. In other words you will rip out you anchor before any of the tackle fails. Certainly that is not good, but using a stronger chain and swivel would not help.
I have read the issue of side-loading a swivel and causing failure and have resisted adding a swivel to my anchor chain until I saw the Mantus design. Clearly Mantus did some out-of-the-box design thinking on that one, and I think they have a superior design result.
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,107
Thinking about chain with a working load of 3900 lbs. what does that mean to our act of anchoring. Really the only experimental effort to explore anchoring in the Sand/Mud of the Puget Sound is Steve with his efforts on SV Panope. He has tried all of the various anchors. He has powered against the anchors. The measured forces turn out to be much less than most of us might imagine. Here is a video with his boat running at greater than 3000 RPM. It translates to 930 lbs far below the working load of most chains, as well as of the Mantus swivel.
Some of his test anchors pull out of the mud at that speed or less.
I like how he gives the anchors a real reversal test. Not unlike the tidal currents.
Search terms: “sv panope anchor reviews”. Select videos.
It looks like a 1200 lbs wll should be satisfactory as most anchors at that level of strain pull out of the bottom. A few do not. That type of strain appears to be extraordinary. One can mitigate such strain on the hardware by selecting a good sheltered anchorage, use a combination of chain and nylon rode, utilize snubbers to take of the shock of boat movement.
Here is a link to a Passagmaker article on anchors, rodes, windage etc. and swivels. The out take is that if a swivel is used it should be attached to the anchor via a shackle and not directly attached to the anchor. Otherwise the article is consistent with the video John posted.
www.passagemaker.com
Hold Fast: A (Somewhat) Scientific Approach to Sizing Ground Tackle
Recently I took a walk down a dock that had a number of trawler-yachts tied up alongside. I was struck by how lightweight the anchors and ground tackle were on
www.passagemaker.com
I ditched the swivel on my last boat after finding a hidden crack when switching anchors. I never had problems with twists, so long as I backed slowly while raising the last bit (the anchor aligns with the water flow--if you are moving forward while raising it will come up backwards every time).
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,107
You do what some of us do not.
Inspect the hardware all the time while using it.
It is the little things that happen all the time on our boats that create the times we tell stories about.
Every time I lower or bring up the anchor I do a visual inspection of the components/splices looking for any changes due to stress, age, wear, etc.
Brought the anchor, swivel and shackle home yesterday after changing the oil in both engines, so that I could get a better read on the various components. A bit of a struggle removing the frozen pin from the shackle. Some WD-40, a hammer and a large wrench did the trick. So what I actually have is a 3/8" swivel, not 5/16". Time to also replace the shackle, which is also 3/8". Both have a 2,200 pound working load. Titan out of Canada makes the shackle and Chicago Hardware makes the swivel. Both are drop forged, heat treated and hot dipped galvanized. I trust Canadian made products. Hopefully, Defender will refund the 5/16" swivel.
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Typically shackles and I presume other hardware is one size larger than the chain. Your 5/16" chain, like mine, has clearance in the links for a 3/8" pin. I believe that using the largest pin that will fit in a chain is normal practice.
Yeah, mechanics and carpenters are always fixing their mistakes!Engineers and architects...
Post wrap up. Defender refunded my mistaken 5/16" swivel purchase, which was much appreciated. The new 3/8" swivel ($5 more than the 5/16" swivel) and shackle went into place and fit perfectly in the same original order; anchor, shackle, swivel, chain link. The old 7/16" swivel pin was quite worn from chain link abrasion; maybe 30%. The new shackle a bit smaller than the original, but the same load rating as the swivel. Rather than keep the old assembly as a spare, even though in fair condition considering its use over many years, it got tossed. I suppose someone on eBay would have purchased it, or I could have mounted it on a plaque as a memento, but ...
Now the time approaches to sea trial the new product, hopefully sooner than later. It does pay to regularly inspect your boat gear before experiencing a failure. I've had my eye on the old swivel for some time and became worried about the amount of pin wear. No doubt it had a few more years of dependable use, but for the skipper, just one less thing to worry about during a strong blow while at anchor.
We had such a blow in Cocktail Cove on Lasqueti Island many years ago. Boat put up such a racket that I could not sleep and spent several hours on deck during anchor watch until the gale abated. Anchor system held with no dragging, but when it came time to leave the next morning, a struggle awaited getting the Danforth anchor unset from China.
Now the time approaches to sea trial the new product, hopefully sooner than later. It does pay to regularly inspect your boat gear before experiencing a failure. I've had my eye on the old swivel for some time and became worried about the amount of pin wear. No doubt it had a few more years of dependable use, but for the skipper, just one less thing to worry about during a strong blow while at anchor.
We had such a blow in Cocktail Cove on Lasqueti Island many years ago. Boat put up such a racket that I could not sleep and spent several hours on deck during anchor watch until the gale abated. Anchor system held with no dragging, but when it came time to leave the next morning, a struggle awaited getting the Danforth anchor unset from China.
I use a Crosby 3/8" shackle with no swivel. Studies performed by Practical Sailor as well as others repeatedly document the distortion and failure of swivels when stressed with lateral loads. Why add an additional mechanical fastener to ground tackle when it is unnecessary especially at significant cost and risk of failure
?