On-Water Boat Anchoring Tips

Originally posted to WaynesWords.com, recreation, by Pete Klocki, March 22, 2009

Comments added by Alan Silverstein are in []. (See also Houseboating 101.)

Pete wrote:

There was a pretty good article in a recent issue of "Arizona Wildlife Views" offering "how-to" tips for on-water boat anchoring. It was written by U.S. Coast Guard Captain, Ed Huntsman. With his credentials, some of his advice might sound a bit over the top for inland waters, but for the same reason, he's not going to advocate any short cuts.

Most of the WW folks already know all about beach anchoring houseboats and larger cruiser types, but on-the-water anchoring is probably not on the radar for a lot of them. But it's an option that offers a lot of advantages that can serve you well at times and shouldn't be dismissed out of hand.

[Conversely, while it's good to have this in your "toolbox", bear in mind the need for anchor chains, and the unusually high risk at Lake Powell of snagging and losing an anchor to a rock.]

An on the water anchorage can save a lot of heavy work lugging big, awkward anchors to shore and either digging them in or stumbling around looking for suitable tie-up points, especially if the intended moorage will only occupy a short period of time. A lunch or dinner stop or an eight hour overnight comes to mind as obvious candidates for an on-the-water moorage. Anchoring on the water also eliminates the possibility of rats, mice and other unwanted visitors hoping to board unannounced. Then too, the back of a drop-dead gorgeous canyon without a single patch of beach sand can offer reason aplenty to drop the hook.

[Note that in many cases there's no need to haul anchors ashore. If your anchor lines end in snap hooks, available from Home Depot for example for about $4 each, you can attach/detach to anchors freely, or just directly hook the line to itself after wrapping it around a rock or a tree.]

Some requisite considerations are necessary before determining that a water anchorage makes sense. The moorage site should be well protected from wind and wake-wave action, have sufficient room to accommodate swing, and most importantly, offer the proper and desired bottom characteristics as well as a workable bottom depth.

And, as you might suspect, having the proper equipment is pretty important too.

Before you can carry on a discussion about anything nautical in nature, however, it's a good idea to have everybody on the same page with the terminology because at times some of the vernacular can leave you scratching your head. If you already know this stuff, forgive me and have patience, because you know there are some folks that don't. Take the term, "Rode", for example. You've heard the word, right? But do you know what it means? How about, "Scope"? Know what that refers to?

"Rode" is the total length of the anchor, chain, and line that is deployed at anchorage. "Scope" refers to the ratio of the length of your "Rode" to the vertical distance from the connection point on your boat to the bottom. (Better read that part twice.) And with that cleared up, here is Captain Huntsman's recommendations for an adequate "Scope".

For short stays during waking hours, a scope of 4:1 is generally sufficient. For overnight stays, he recommends a scope of 7:1. Now what, exactly, does that mean in lay terms?

Let us say that the connection point of your anchor line is two feet above the water and you propose to anchor for a lunch stop in eight foot deep water. Using Captain Huntsman's advice, a 4:1 scope (ratio) would require a "Rode" of forty feet (8+2 = 10 x 4 = 40) See how that works? And if you decide to spend the night and adhere to the 7:1 rule, you would need a rode of seventy feet (8+2 = 10 x 7 = 70).

Now, all of that may sound a little too technical to keep tucked behind your ear. But there are some practical short cuts you can use to take advantage of these pearls of wisdom without committing the math to memory. With the formula in mind, let us assume your available anchor line and chain is 100 feet long. For overnight stays, what would be the maximum water depth that you can safely anchor in? Run the math backwards for the answer. It comes out to twelve feet, with a little bitty cushion for error. (100 divided by 7 gives you 14.2 feet, less 2 feet from bow-eye to water = 12 and change.)

So, if you have a 100 foot anchor line, all you need remember is that 14 feet or less is a safe anchorage "scope" for you, and the actual water depth should be 12 feet or less. Simple.

However, there is an assumption that follows. It is that the anchor attains an effective bite on the bottom. And for that to happen, there are two requisites. They are, first, a suitable bottom and second, a suitable anchor that is weight-rated for your boat, based on the material the anchor is made of.

Traditional Danforth type anchors are made of galvanized steel. But aluminum models are also available. These weigh roughly half as much as steel anchors do, without sacrificing much in holding power. Here are some comparisons between the two different materials;

Aluminum  4 lb anchor versus  6- 9 lb steel for boats up to 27 feet.
Aluminum 10 lb anchor versus 14-18 lb steel for boats up to 38 feet.
Aluminum 21 lb anchor versus 33-50 lb steel for boats up to 50 feet.
Aluminum 47 lb anchor versus 70-90 lb steel for boats up to 68 feet.

There are several different anchor designs with some only marginally more effective than others on different bottom characteristics. Those in common use include the "Danforth" designs, the Plow, Kedge, Claw, Grapnel, Box, Navy, tri-fluke river anchors and Mushroom types, with the Danforth likely the most popular on Lake Powell. None of the various types will perform as intended and desired however, without the aid of a length of chain shackled between the anchor eye and the spliced thimble-end of the anchor line.

The chain serves multiple purposes. Its weight allows the anchor to absorb the shock and to remain at a flat angle as wave action pitches the boat's bow and line up and down. The chain also protects the line from abrasion at the points of bottom contact. Though less important with beach anchors, a length of chain at the terminal end of the water-anchorage rode is mandatory.

The question then is; how much chain is necessary? And here I have to back away from Captain Huntsman's advice somewhat. He recommends one foot of anchor chain for each foot of the boat's overall length. I think that's probably a lot more than we actually need in a protected anchorage at Lake Powell. Anchor chain is heavy and does not handle as easily as rope does. Beyond that, I just don't think it is practical for folks with a 25-foot cruiser to try to hassle and store 25 feet of anchor chain.

So how much chain is enough? Since we are talking about protected anchorages in relatively shallow inland waters as opposed to offshore ocean anchorages, I'd guess you could halve the Captain's recommendation and be none the worse for wear.

Not all chain is created equal. Anchor chain is not just any old piece of chain. It of course must be rust-proof, and it must also be stronger than average for its given weight and size. To achieve a rust-resistant quality, most common anchor chains are made from hot-dipped galvanized, high-test chain steel. Higher end stuff is made from stainless steel. Both are heavy and both are expensive. Grade-40, 5/16-inch "galvi" chain will weigh approximately one pound per foot and will cost about $4.50 per foot and up. It will give you a breaking strength of around 11,000-plus pounds, enough to handle most boats to 45-feet in length, so the cost is easily justified.

Quality anchor rope isn't cheap either. Here, 3-strand nylon rope is the most common material and braid type, and gives better than average performance-bang for the buck. Its properties allow a good deal of load-stretch to soak up shock, its strong for its diameter, is rot and UV resistant and handles fairly easily.

Some recommended line diameters for 3-strand nylon are;

3/8-inch  4400 lb break-strength for boats to 24 feet
1/2-inch  7500 lb b/s for boats to 32 feet
5/8-inch 12000 lb b/s for boats to 40 feet
3/4-inch 16000 lb b/s for boats to 48 feet
  1-inch 22000 lb b/s for boats to 65 feet

Choosing the ideal bottom for your anchorage just requires a bit of common sense, The best bottom will be one that is fairly flat and sandy. And if you are limited to twelve foot depth or less, there's a fair chance you will be able to see and evaluate the bottom conditions before you are committed.

Hard rock bottoms of either slick rock or broken rock should be avoided. The anchor that will hold on slick rock has yet to be invented. And anchoring on a broken rock bottom is an excellent way to loose an anchor. If your hook becomes wedged, you may be left with no option but to cut it loose and give up both your anchor and the chain.

When paying out or taking in an anchor rope, be kind to your hands and remember to wear a pair of stout gloves. Tumbleweed thorn, cactus needles and even an occasional fish hook can imbed itself in the rope's fibers and give you a nasty surprise as the rope slips through your hands.

Even if you never plan or intend an on-water anchorage, its good discipline to be properly equipped and ready to deploy an anchor in case an engine or some other equipment failure strands you and a beach tie-up is not a practical option.

Give an on-water anchorage a try some time. If nothing else, as a drill to see how it is properly done in the event it becomes a necessity.

And who knows, you just may become, "hooked".

-- Petester