Swivel Anchor Chain Joint

Vyv Cox says that it’s all good to have a strong anchor, but it’s equally important to have a ground tackle that will keep you safe.
With the emergence of new materials and designs, the improvement of equipment used in other technologies or the improvement of existing items, the equipment used to anchor our ships is constantly evolving.
It can be said that the entire ship that connects the anchor to the ship is composed of many different parts, at least as important as the specification of the anchor.
If you correctly understand the capabilities and limitations of the ground block and then set it up, you can be sure that the controversial “weakest link” will not get you into trouble.
Riding (called “cable” in older age) refers to the connection between the anchor rod and the fixed point at the other end of the ship.
Usually refers to full chain riding or hybrid riding, that is, chain and rope, but in fact, the term also includes any component used to connect any part of it together.
In many cases, there is no problem with the chain winding. This is right. If you find you need it, my own motto is to install it, but that’s not the case.
My choice is to install one, because it will make it very easy to rotate the anchor bolt after restoration, and “error” will inevitably occur. This may even be necessary for some self-starting and restoring anchor bolt systems. Indispensable.
Some chains will twist naturally, which may be due to uneven wear on adjacent links, and certain shapes of anchors will rotate violently when restored.
If you find that the chain is often twisted or twisted in the locker when recovering, it may be that the swivel will help.
The pins of 10mm shackles can pass through 8mm links, and most modern anchors are slotted to allow the eyes of the shackle to pass through.
The “D” shape seems to provide better straight-line strength, but the bow shape seems to be more able to cope with changes in the direction of tension.
The reality is that when I destructively tested the two types, there was no significant difference between the two shapes.
The stainless steel shackles purchased by Chandler are generally stronger than their galvanized equivalents, as shown in Table 1 below.
However, if we look at the galvanized alloy steel shackles used in the lifting and lifting industries, we can see that, for example, the Crosby G209 A series in Table 2 is much stronger than any tested “offshore” product .
Similarly, the strength provided by heat-treated alloy steel greatly exceeds the data obtained from miscellaneous purchased items, Table 3.
One end of it is tied to an anchor chain, and the chain between the anchor chain and the anchor is shorter.
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I tested the Osculati crank swivel joint with the same principle, but based on my experience, I found that it can inhibit the solidification of the anchor.
The market offers a variety of dazzling swivels, from roughly galvanized designs that cost less than £10 to exquisite artwork of foreign materials, all with prices as high as 3 figures.
A budget-conscious connector will be quite lightweight and will rely on two metal rings that are bolted together, as shown in the lower right picture.
Anchoring the swivel will help eliminate twisting, but the straight side arms may fail under side loads
This design is widely sold in vending machines and mail-order stores, but any design that relies on bolted parts to carry the load of the chain or anchor may have poor load capacity, so it is best to avoid it.
In the destructive test, the only rotary joints I conducted with higher strength than the chain to be connected were those in which two forged parts (Osculati and Kong) were simply fixed together by bolts.
In this case, the strength is provided by the forged structure, inherent strength and toughness, as shown in the figure below.
The only possible weakness is that if you want to loosen the connecting bolt, then I always use some thread locking device on the rotating bolt.
The disadvantage of the type shown is that although the design usually provides side load carrying capacity comparable to the SWL of the chain, any angled load on the end of the anchor tends to bend the parallel arms of the swivel.
I devised a simple method to avoid this problem. The problem has been reported in YM (2007) and is now widely used in anchoring recommendations.
Adding three chain links between the swivel and the anchor can retain its advantages while being fully articulated
This is to add two or three links between the rotation point and the anchor point, thereby realizing the overall articulation.
Recently, several manufacturers including Mantus and Ultra have introduced compact, expensive designs that achieve articulation by eliminating side arms.
The top rotating device shown above is Mantus, which uses a built-in bow-shaped shackle and forged pins to bear the chain load, while below, the Ultra flip rotating device uses two forged pins and uses ball joints, which is more articulated than parallel The side arms are better, up to a lateral displacement of approximately 45o degrees. Vathy makes a similar rotation.
If the anchor is wedged into the rock and the tide direction is reversed, it is conceivable that although the manufacturer claims that the breaking load is higher than the chain load, the rather narrow neck may be subjected to higher bending loads.
As a rough guide to the correct size chain for your boat, in an 8mm 30-level chain, long enough to 37 feet, 10mm to 45 feet and more than 12mm is sufficient, but the boat’s displacement is an additional factor.
Obviously, the chains required for weekend pottery and extended high-latitude cruises are also different.
A good way to determine the size of a chain is to look up grocery websites that have good information.
When cruising the Irish Sea, my range was only more than 50 meters, but for a longer cruise, I extended it to the current 65 meters.
Some remote areas have deeper water anchorages, which may take up to 100 meters in length.
Yachts intended for extensive cruising are likely to carry a distance of 100 meters, ie 8 mm weighing 140 kg, 10 mm weighing 230 kg, and stored in the forward position, which has the least impact on sailing performance.
For example, referring to Table 4, an 8mm long 70-level bearing 100 meters instead of the same length of 10mm 30-level can save 90 kg of anchoring lockers and almost double the strength of the rider. 4,800 kg increased to 8,400 kg.
Marine chains up to 12mm in size are mainly produced in China, although one or two European manufacturers continue to produce them.
The nominal grade of the chain is 30, but tests show that the UTS number is close to or even exceeds the value required for 40.
Many manufacturers have reduced the thickness of zinc in the production chain. As a result, many buyers find rust after only two or three seasons.
It is almost rust-free and its smooth surface will not accumulate in the locker, but its cost is about four times that of a galvanized chain.
Mantus (pictured above) and Ultra (pictured below) are modern turntables designed to eliminate the weaknesses of early turntables
The main advantage of hybrid riding is weight reduction, which is ideal for smaller or lighter yachts, especially catamarans.
The rope of the hybrid fishing rod can be three-strand or octopus. If you need to pass through the windlass, you can splice any of them to the chain.
Instructions for this operation are widely available on the Internet, but it is necessary to consult the windlass manual to determine the precise type of joint that will pass through the Gypsy.
Nylon may be the most widely used material for this purpose, but polyester is also used. Nylon has greater elasticity, especially the three-strand form. Although the three-strand nylon becomes very hard and difficult to bend after a period of time, this is China is not ideal. Anchor ride.
Elasticity is very ideal, it is provided by the buffer in the whole chain, but it is inherent in the hybrid type.
The mid-term problem with joints is that the rope stays wet for a long time, leading to premature corrosion of the chain.
For boats without windlasses, or boats used for wedge shapes, it may be more convenient to splice a thimble to the end of the rope to fasten it to the chain with a shackle.
For most anchors in the mid-tide range, only a chain is used, which avoids the trouble of sometimes sending the rope into the chain locker, or worse, water inflow from the sprinkler pipe.
Sometimes it is necessary to connect two or more lengths of chains required to pass through the windlass.
This may be due to the decision to tow a longer chain due to the constantly changing cruising ground, or simply because some corroded chain links need to be removed.
This clever little device consists of two halves of a chain link, which can be riveted together to form a single chain link.
When a C-shaped chain is formed and made of the same material as the chain, its strength is about half that of the mild steel chain to be connected.
Therefore, the strength of a high-quality C-chain made of heat-treated alloy steel is about twice that of low-carbon steel.
The unfortunate fact is that the vast majority of C-links sold in the gondola are made of mild steel or possibly stainless steel.
We once again turned to the lifting and lifting industry, where we found that the alloy steel C-links will not damage the strength of the chain.
Because they have been quenched and tempered, a lot of effort is needed to rivet them.
If you pay too much for the chain, or if the winch fails without doing so, it can easily cause the ground block to be lost.
If the anchor is dirty or you need to let go of the anchor in an emergency, then you must be able to let the anchor run under load, and the only reliable way is to tie the end of the chain to a dead corner and stare at the anchor. The locker can be cut quickly if the chain needs to be released, or it can be untied and fixed to a large fender.
Is the bulkhead fastened with bolts and is there anything to distribute the load to the other side?
The bitter taste of the rod should be firmly fixed to the fixing point of the locker, but it must be easy to loosen in an emergency
C-Link is used to connect the chain. Put the two halves together, hammer the rivet into the hole with a hammer, and then drift until it is completely fixed
The nominal grade 30 chain is probably the most widely used chain and is usually completely reliable, but if the size of the boat is insignificant for the recommended size, increasing the slope can provide greater strength without the need for replacement Winch winch.
The type of rotary joint should not rely on bolts to carry the anchoring load, whether it is an anchor or a chain attachment.
Use swivels only if they are found useful, as they are not essential and will cause weakness in riding.
Nylon rope has greater elasticity than polyester rope, and the three-strand structure has greater elasticity than octagonal folds.
The strength of the alloy steel C-type chain in the lifting industry is as strong as the 30-grade chain, but it is not recommended to use a higher-grade chain.
Vyv Cox is a retired metallurgist and engineer who usually spends six months a year on his Sadler 34 in the Mediterranean.
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Post time: Jan-20-2021