When you think about anchoring, you probably just picture the anchor falling to the bottom and grabbing on with its flukes, and then the anchor rode holding the boat to the anchor. The anchor doesn't move, and neither does the boat! Simple!
The truth is very far from this ideal mental image of anchoring. There are materials and calculations that need to take place for the anchoring to work successfully.
While the anchor itself is an important topic for discussion, we will ignore the different brands and styles of anchors out there and simply picture the perfect anchor (whichever anchor you wish that to be) and simply focus on how the anchor is connected to the yacht.
Boats have ropes on them! So naturally, the first material of thought for an anchor rode would be nylon line. It is both stretchy and strong, so why not tie the anchor rode to the anchor using an "anchor hitch" and all it a day! Nylon rode has the advantage of stretch, but it is very succeptible to chafe. There is little chafe as the line runs through the water, but considerable chafe as the line meets the anchor.
The anchor lives on the bottom of the sea floor, and the shank is usually in very close proximity to this area. This means that the rode will be laying on the sea bed as well and will rub against many items that can chafe through the line.
To alleviate this issue, a length of chain can be added between the anchor and the rope, this will take the brunt of the chafe like a champion, and allow the rope to complete the journey up to the vessel. Chain adds considerable weight to the system as well, and weight near the shank will help pull the shank parallel to the bottom and aid the flukes to dig in and hold well.
If a little chain is good, why not make the entire system out of chain! This would be by far the strongest system, and also the heaviest. The weight of the chain suspended between the bow and the anchor will form a catenary curve that will help pull laterally on the anchor and keep it dug into the bottom.
Chain is not elastic though, and the only elasticity in the system will come from the catenary curve being consumed as wind and waves push the bow back in a surge. As the bow pushes aft, the curve will flatten out and then the weight will pull the bow forward again until the curve is re-established. This works well for moderate to light conditions, but in heavy conditions, this curve will be blown straight and the shock loads will be transmitted to everything in the system. To prevent the cyclical and damaging shock loads, a nylon snubber can be tied between the bow and the rode, taking the force of the last few feet of the rode and offering some much needed elasticity.
Your choices are very simple when deciding what type of rode to employ. You can either use all rope, rope and chain combination, or all chain. Naturally, the longevity and price will go hand in hand. Rope is the cheapest and will last only a number of years, while chain will be the most expensive and will last decades if well cared for.