By: Alex Blackwell
The rode (also known as anchor cable) is what connects your anchor to the boat. Without it your anchor is not going to do you a world of good. It is consequently an important part of your tackle and worthy of some serious consideration.
Wave and wind action will cause the boat to move. In storm situations this movement can be quite violent. As the anchor is (hopefully) firmly embedded in the seafloor and the other end of the rode securely connected to the pitching boat, this energy must be absorbed by the rode. This energy absorption is referred to as ‘dampening’.
Without adequate dampening, these forces are exerted directly on the deck hardware and on the anchor. The boat’s motion might thus result in catastrophic deck hardware failure or in the anchor being pulled free from the bottom. Therefore, a rode should have good dampening characteristics.
The rode needs to have ample strength to hold your boat without breaking even under extreme loads. Squalls can and will occur and winds can suddenly go from a benign 10 knots to an uncomfortable 50 knots exerting strong loads on your gear. The rode also needs to be resistant to abrasion or chafe, as well as to UV light, or it will fail. And finally, it needs to be relatively easy handle and store.
Originally all ropes, including rodes, were made from natural fibers such as manila, hemp, linen, cotton, coir, jute, silk, wool, hair, or sisal. This has been succeeded by synthetic fibers. One characteristic shared by all ropes is that their fibers are exposed to abrasion. We discuss how to protect against this here.
Nylon (polyamide) with its excellent elasticity (18 to 25%) and resistance to ultraviolet light has for many years been the rode of choice. Polyester (Dacron®) and blended ropes are gaining traction today for rope rode. Polyester has about 90% the strength of nylon but stretches less under load. It is more abrasion resistant, has better UV resistance, and has less change in length when wet. You can easily overcome the loss in dampening by letting out more rode. Double the length of rode provides double the dampening.
A cheaper alternative is polypropylene. It is preferred by fishermen for their pots as it floats as opposed to nylon or polyester which sink. Polypropylene is not as strong as nylon rope. Furthermore, polypropylene suffers badly in sunlight, losing much of its strength in as little as a year.
Rope Rode Characteristics
An all rope rode has the advantage of being light, elastic and generally easy to handle and store. However, external abrasion or chafe, where the rode comes in contact with another object on your boat or on the sea floor, and internal abrasion of the fibers, when the rode stretches and contracts repeatedly, can significantly impact its overall strength as well as its life span.
Twisted or Laid Rope
The traditional method of making rope is for it to be twisted or laid.
One property of laid rope is partial untwisting when used. This can cause spinning of suspended loads, as well as stretching, kinking, or hockling of the rope itself.
With braided rope, the yarn is braided rather than being twisted into strands. Double-braided rope has a braided core with a braided cover.
Chain has a very high tensile strength, and is very resistant to chafe. Because of these characteristics alone it is used as a rode by most long distance cruisers as well as on larger vessels. Its weight helps it easily fall into an anchor locker.
The downside, however, is that chain is heavy, and this can be very relevant with the lengths needed for an all chain rode. With an all chain rode you will most likely need a windlass. The chain rode and windlass add a lot of weight to the vessel’s bow area, and so may affect performance underway. The other downside is that chain does not stretch.
Because of its weight a chain rode will sag in light to medium winds requiring significant energy to straighten it out. This catenary effect provides excellent energy absorption.
The energy required to straighten the sag in the chain is called catenary and this in turn provides excellent energy absorption in light winds (up to about 20 knots). The sag in the chain also gives the rode a good angle of pull on the anchor.
In strong wind situations when elasticity is needed most a chain rode will provide absolutely no energy absorption. Chain does not stretch, and when the wind picks up it literally goes bar taut, transferring all the shock loads caused by wave and wind action directly to the anchor and deck fittings. This may in turn cause the anchor to break out or a deck fitting to fail.
Though much touted, the catenary effect is thus actually of little consequence while a vessel is at anchor. On the positive side, while anchoring and setting the anchor, the chain does help by improving the initial angle the anchor addresses the bottom.
When bar taut a chain rode has no stretch, no catenary and thus no energy absorption. It also will provide a less than optimal angle at which it addresses the anchor.
Finally, chain can have a tendency to hockle if twisted. This is particularly problematic if it happens in the chain locker as it may jam while being fed out of the navel pipe (or spurling pipe).
Combination Rope and Chain
When one considers the characteristics of either an all chain or an all rope rode, with each one having significant positive attributes plus specific downsides, a combination of the two might be beneficial.
With a combination of chain and rope, chafe is avoided and the angle the rode addresses the anchor is improved in light to moderate winds.
The weight of the chain improves the angle with which the rode initially addresses the anchor and may provide further dampening to reduce tugging on the anchor and deck hardware in light winds. It also helps to reduce chafing of the rode on rocky, coral, or abrasive bottoms.
Likewise, as we have seen above, the shock loads are transferred directly to the deck hardware with an all chain rode. This also applies to the shackles, swivels, and so on, as well as to the anchor irself. For an all chain rode, it is thus always recommended to add something to absorb these shock loads. This can be a length of stretchy rope to connect the chain to the boat. This rope provides the chain rode with elasticity and is called a snubber.
The snubber or mooring compensator is most commonly hooked (or tied with a rolling hitch) to the chain and then tied off to a cleat on the boat. Whereas the chain is also connected to the boat, it is left loose so that the snubber may absorb the impact of any wave action. If the snubber were to fail, the chain is still there to hold the boat.
Alex and Daria Blackwell are the authors of “Happy Hooking – The Art of Anchoring.” It covers every aspect of anchors and anchoring in a fun and easy to read format with lots of photos and illustrations. It is available in print and Kindle from CoastalBoating.net, amazon worldwide, & good chandleries.