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GETTING STUCK - A LOOK AT GROUND TACKLE FOR OUTBOARD BOATS

Posted 4/11/2012

“Getting stuck” isn’t usually a welcome boating term unless you are anchoring your boat. Unfortunately, too many boaters are unfamiliar with anchoring systems, how to select the right components and how to deploy them correctly. The anchor serves a variety of functions when boating and fishing, but your anchor can also be a safety item of last resort should you find yourself without power with the wind blowing your boat ashore, or on a river being swept away into whatever lies around the next bend. Needless to say, it’s important to be prepared with the right ground tackle. 

“Ground tackle” is boating jargon for the anchor system, which consists of the anchor, a length of chain, shackles and nylon rope. Ground tackle components vary in size, weight and strength according to length and type of boat, but for most outboard- powered boats in the 15-to 40-foot class, the basic set up is similar. 

There are a number of anchor designs on the market, but two are highly recommended for most boats in our target size range, the Danforth and Fortress styles. They are similar in appearance and operation, but the former is made of galvanized steel, and the later of high-tinsel strength aluminum and therefore considerably lighter. They come in sizes for use on power boats from under 15 feet to in excess of 100 feet, and both are easily recognized by their two pointed flukes attached to a stock, which pivots on a center shaft called the shank. When deployed, the flukes dig into the bottom and can hold in a wide range of bottom compositions making them the most versatile anchor styles with the widest range of applications. 

When purchasing a Danforth or Fortress anchor, refer to the manufacturer’s application guide to assemble the components necessary to create a working anchor system. The anchors are rated by holding power, which is determined by the boat length, boat type, and the wind conditions you might encounter in most cases. The basic anchor application chart is for winds up to 20 knot, but if an operator anticipates anchoring in higher winds, anchor size should be chosen accordingly or a second “storm” anchor should be kept aboard for those conditions. Regardless, it never hurts to purchase an anchor one size larger than what is recommended for your boat size to play it safe. A slightly larger anchor will hold better on a shorter “rode” (the length of rope between the boat and the anchor) and makes anchoring accurately for fishing purposes an easier proposition.

The anchor is attached to a length of chain using a shackle. The chain can act as a chafe guard when anchoring on rough bottom, but it’s the weight of the chain that is important for helping set the anchor. Chain and shackle sizes are matched to the anchor size using an application chart. Chain length is determined by the maximum depth of water you might encounter with the rule of thumb being six feet of chain for every 25 feet of depth. For example, if you will encounter anchoring situations in water as deep as 75 feet, not uncommon for fishermen anchoring over bottom structure, your ground tackle should include 18 feet of appropriately sized chain.

Anchors are rated by holding power, which is directly affected by the scope of the chain and rope. The higher the wind condition the more holding power is needed for the anchor to maintain its grip on the bottom. If the pull exerted by the boat is too direct, like the boat in this illustration at the far right, it can dislodge the flukes from the bottom dragging the anchor and setting the boat adrift.

Nylon anchor rope is also selected so its strength will match the stress the boat can exert on it laying at anchor, and it should include a spliced thimble at the end where it attaches to the chain with another shackle. Multi-strand nylon is preferred because it stretches, which acts as a shock absorber between the boat and anchor. The decision on how much anchor line to purchase should be considered carefully because this is where many boaters fall short. One of the key determining factors in making sure your ground tackle effectively holds bottom is the angle or scope of the rope between the boat and the anchor. The deeper the water, the longer the rode necessary to hold bottom effectively. Under light wind conditions, a minimum of a 3:1 ratio of rode to depth is needed to achieve the minimum holding power of 30 percent of the anchor rating. As you lengthen the rode, holding power increases (5:1 – 70 percent; 7:1 – 85 percent; 10:1 – 100 percent). So for a vessel anchoring in water as deep as 75 feet, it should have a minimum of 600 feet of anchor line. 

The scope, or angle the boat pulls on the anchor, is a function of the length of the rode in relation to the depth of the water. In this illustration 100 feet of rode is being used in 20 feet of water, a 5:1 ratio, to achieve 70 percent of the anchor’s rated holding power. Deeper water requires a longer rode to achieve the proper scope. The stronger the wind or current pressure on the boat the more critical it becomes to use scope to attain maximum holding power.

Deploying ground tackle takes a little know how and practice. Under average conditions, the first thing to determine is where you want the boat to come to rest. Then check the water depth so you know approximately how much line will be needed to hold under the prevailing wind and current condition. Once these variables are established, you can determine where to position the anchor. 

Drop the anchor from a stationary boat until it hits bottom, and then very slowly power back in reverse paying line out as you move. As you begin to approach your chosen position, apply hand pressure to the anchor so the flukes will begin to penetrate the bottom. When it grabs, wrap the line around the bow chock of the boat and power back gently with the engine to firmly set the anchor. The anchor is set when the boat is stopped. This is called power setting the anchor, and it provides a firm hold to the bottom. You can now adjust the length of the rode for the final positioning of the boat.

This chart shows the increase in holding power achieved by maintaining proper scope. When sea and wind conditions are mild 40 percent to 70 percent of the rated holding power is sufficient and is achieved with a scope ratio of 3:1 to 5:1. When wind and current conditions become stronger more scope is required, from 7:1 to 10:1, to achieve the maximum holding power of the ground tackle.

Anchoring effectively and safely is a skill every boater should learn. This article just scratches the surface as there are a number of techniques for use under varying conditions that can be encountered. Being prepared with the right ground tackle will make your boating experience safer and more rewarding.