1st, estimate the depth of water where your anchor will lie at the highest tide point of your stay, then make a decision about the length of rode to let out.

• For chain rode, use 50 ft (15 m) plus 2 times the depth
• For Chain and Rope combination rode, use 50 ft (15 m) plus 4 times the depth.

Take a look a position D on the chart above; the depth is at least 30 meters (100 ft) deep at low tide. With chain rode, you would need to let out 75 meters (250 ft) if there was no tide change. Or if there is a 2-meter tide range then add another 4 meters to the amount required. Most boats don’t carry that much. Typically they carry about 50-60 meters of chain, which limits your maximum depth at high tide for anchoring at about 15-25 meters (50 – 80 ft). So position D is pretty much out.

Surrounding obstacles can be rocks, shallow areas, or even the beach area. The danger is calculated by knowing how much anchor rode is let out and then allowing for a full 360 degrees swing in the night. So for example, if you have 60 m (200 feet) of rode out then your anchor had better be more than 60 m away from any area in every direction that is shallow enough at low tide whereby your keel might hit, including the land or submerged rocks. So even if you think you could tuck in enough on area D to get to the shallow area, you are still too close to land to allow for any swing in the night. In area A1, there is a drying area of land at low tide. This means when you anchor you need to stay far enough out to not hit the bottom. Area C2 is also a concern, it is doubtful you could anchor in shallow enough water and not swing into the land. If there is a steady easterly (out of the east) wind predicted you might argue that C2 could be done since swing is unlikely. However, if you observe the rate that the bottom drops off, if the anchor drags a little, it will move into deep water quite fast which reduces your holding power and thus may allow you to completely drift off anchor. Also, view the contour lines on land. If there is a steep cliff there, even a steady easterly wind can create some swirling of wind. C2 is just not a great idea.

Tide range affects your scope as the tide rises and drops. A rising tide increases the depth and thus to anchor with proper scope, you must allow for the maximum depth the water will get to. e.g. if you anchor in 5 meters (16 ft) of water at low tide and the tide range is 3 meters (10 ft), then you must consider the depth to be 8 meters which gives rise to 39 meters of chain (120 ft). A lowering tide makes the water more shallow and thus your swing distance is increased. e.g. if you anchor in 5 m of water at high tide and the tide range is 3 meters then there will only be 2 meters (6 ft) under your keel (make sure you know the zero datum point of your depth sounder – hopefully it is set to be the bottom of the keel – or in this case if the zero datum was at water level you could be grounding at low tide). Assuming you know the datum is at the bottom of the keel and you let out 40 meters of chain to begin with, you’d better make sure that there is plenty of depth within 40 meters in all directions. Considering you’re already at 2, this is doubtful.

The seafloor type is a critical factor. Certain anchors hold better in certain bottom types. Look on the chart to find out the seafloor type where you are anchoring. At position A1, the seafloor is weed. Danforth anchors don’t do well in weed for example. It is always a good idea to know your anchor type and know what bottom types it works best with and what bottom types it works worst with. Plan on ( if practical) to dive the anchor with a snorkel to make sure it is dug in well.

Being sheltered from the wind provides for two things; one, general comfort and two, it reduces the force exerted on the anchor. Wind gusts can exert an enormous amount of force on the anchor and cause it to drag or worse yet – to pull out completely. As examples, the below lists which anchor spots might be best with varying wind directions (wind direction is always announced as where it comes from – Easterly wind comes from the east).

• Northerly: A1, A2
• Southerly: E, F, B, B1, and possibly B3 (B3 better for SE direction)
• Easterly: C1 and possibly F in behind the marina
• Westerly: E, A1, A2

Of course, the Marina is always a safe choice. But $$$.

Waves are the sworn enemy of anchors. They shock load the anchor and drag it a little with each wave. The further from the protection of land the greater the size of waves. Waves also are annoying in that they change direction as they pass by a land mass. Below we show these phenomena.