While cruising without any real schedule and on a well-found boat, we are truly fortunate to be able to just “drop the hook” whenever and wherever we want (well, pretty much). We have gratefully spent time at anchor in some of the most beautiful areas of the southeast coast.
LOCATION, LOCATION, LOCATION
In deciding where, and how, to anchor, there are a lot of variables to consider. Some popular anchoring areas are marked along the routes we use in several of the crowd-sourced charting applications (green icons below).
This data is nice because there are usually reviews of the anchorage and sometimes helpful descriptions of relevant information related to safe anchoring. Alternatively, there are often areas on the nautical charts that look secure based on geographical formations when coupled with the predicted weather for the area.
Once a potential area is selected on the nautical chart, several variables need to be considered, regardless of any “review” comments available, as in the end you are the captain of your boat and are responsible for all decisions. Tidal range, forecast wind direction, current, and water depth all affect the anchoring strategy. If there are no other boats in the same area, then some of these items become less critical than others.
Typically, a location is chosen that is protected by land from the forecast wind direction. This will keep any wind-driven waves small, making the boat much more comfortable overnight.
The proposed anchoring location should be well away from any navigable waterways,
channels, and normal boat traffic. The water should be shallow enough to allow the anchor to reach the bottom. The tidal range should allow the boat to have plenty of water under it at the predicted low tide level.
SCOPE
The primary consideration for anchor location is water depth. This will determine how much chain or rope, called rode, is put out to the anchor. An anchor needs some amount of horizontal pull in order to stay attached to the bottom. Typically, the more horizontal pull, the stronger the anchor can hold.
The ratio of the depth of water to the amount of anchor rode deployed is call the scope. Depending on the expected weather conditions, more or less scope is typically used.
Source: http://www.boatus.com
SWING
The next consideration is nearby hazards – shoals, shorelines, or other anchored boats. If there are nearby boats, then the possibility of collision during the night needs to be considered as the boats all move about their anchor positions.
When there are several boats all anchored together, one can sometimes see that they all point in the same direction as they move around. The direction that a boat points while at anchor is affected by a complex combination of the wind above the water and the current below.
The wind’s effect on a boat at anchor is determined by the shape of the boat above the water – masts, deck house size, enclosures, etc. Conversely, the current’s effect on a boat at anchor is determined by the hull shape under the water, primarily the keel.
If all of the boats are similar, e.g. sailboats with masts and deep keels, they tend to behave themselves and swing around their anchor similarly. Because of this, they can anchor quite close together and not interfere with each other as the wind and current conditions change.
If however, a trawler or power boat is part of the mix, it may swing in a completely different direction than the other boats with the varying wind and current since both its above the water and below the water configuration is different. This means that the anchoring distance should be increased relative to the other boat types.
The area covered by a boat moving around at anchor is called its swing radius. It typically appears as a circle around the point that the anchor is set as the wind and current move the boat around.
Source: http://www.boatus.com
Again, scope, rode type, tidal range, and the resulting swing radius all come into play. For example, one can see in the geometry of the above diagrams, as the tide goes down or up, the size of the swing radius will be affected – as only one portion of the scope ratio is changing. These things must also be considered when planning for a safe anchoring position.
ANCHORS
Still another consideration is the makeup of the bottom in the location – mud, sand, rocks, etc. The type of bottom is sometimes indicated on the nautical chart, sometimes stated in reviews of anchor locations, and/or can be inferred by the surrounding geography.
Different anchor designs perform better or worse in different bottom types. This is why one sometimes sees more than one anchor style fitted to different boats. SCOUT has two different types of anchors on the bow – each can be deployed for different types of bottom condition encountered.
As expected, anchor manufacturer’s marketing claims of performance in various bottom types, for every anchor design, are the subject of endless dock and internet forum discussions.
RODE
The rode on most boats is made up of either rope or chain. A chain rode, due to its heavy weight, has many advantages (as well as some disadvantages). One advantage is that the chain itself will create a “mini anchor” at the bottom when the wind and current conditions are light. A boat with an all-chain rode will swing in a much smaller diameter area for during these light wind times.
Another advantage of the heavy chain is that the “pull” on the anchor is kept more horizontal (better) for a longer period as the wind increases and loads are placed on the boat and anchor system. Rodes made up of rope typically have several feet of heavy chain connected to the anchor, ahead of the long rope, for just this purpose. Because of this heavy horizontal pull, an all-chain rode can typically use smaller scope when compared to rope in the same conditions. Chain (vs. rope) near the anchor also helps with chafe where the horizontal part of the rode lies, especially on rocky or coral bottoms.
Finally, the big “droop” caused by a heavy chain rode can create some “elasticity” as waves pushing up against the boat cause shock loads to the boat and anchor system.
The primary disadvantage to the chain is the very heavy weight, typically stored in the bow, as well as the cost. The weight of deploying and retrieving chain also makes for a difficult time in smaller boats, those having a manual retrieval method.
SCOUT has two lengths of 250ft of 3/8” chain connected to each of the two anchors.
WINDLASS
One convenience that many boats have as part of their anchoring system is a windlass. This is a (typically) electric motor-powered spool that aids in retrieving the rode and bringing anchor back aboard the boat. Some boats with simple electrical systems use a manual windlass which uses a ratcheting arm for operation.
For a boat with all-chain rode, a powered windlass is a great convenience. The heavy weight of the chain or anchor does not have to be manhandled. Typically, a foot switch at the bow allows control of the windlass to let out or retrieve the rode.
Here is a short clip of the windlass on SCOUT bringing up the last bit of rode and anchor for an early morning departure. SCOUT has a small pump installed, called a “washdown pump”, that pumps seawater up from under the boat and out onto the deck so that the mud can be washed off the chain and anchor prior to stowing for the day.
COMPLICATED?
This is by no means a complete treatise on anchoring. There is a myriad of additional topics like bridles and snubbers, catenary, kellets, backing down on the anchor, etc. that are argued and talked about ad infinitum at marina docks everywhere and on internet forums. Every captain ends up adapting their processes to what they are comfortable with.
While all of it does sound quite complicated and tedious to process every time one stops for the night, it really is not a big deal. As more and more anchoring (and learning!) is done, and the results evaluated, a lot of it becomes just second nature.
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