234 seamanship secrets
rode should be 7:1, or 7 feet of rode for each foot of the above-mentioned factors.
Make the scope 10:1 in exposed anchorages or storms.
You are going to anchor in an area where the water is 15 feet deep at low tide,
the tidal range is 8 feet, and your boat has 3 feet of freeboard. For a 7:1 scope,
you’d use 182 feet of rode, as shown in the equations below:
15 + 8 + 3 = 26 feet
26 feet × 7 = 182 feet
Notice what happens if you forget to factor in the tidal range and freeboard.
15 feet × 7 = 105 feet
105 ÷ 26 = 4:1 scopeTh e Five-Factor Guide to a Secure Anchorage
The following five factors add up to a secure anchorage.
- Seabed. Your anchor must be able to penetrate the seabed and hold. In
Chapter 1, we discussed how to interpret seabeds on a chart. Study the chart
to choose the best anchor based on the type of bottom. Th e best holding
ground consists of hard mud or clay. When in doubt about the seabed
quality, use a larger plow or claw anchor. - Wind, sea, and groundswell protection. Th e ideal anchorage provides
wind and sea protection from at least three sides. In areas with steady winds,
choose a cove protected from the dominant wind direction. In areas with
shift ing winds, make sure you will be protected aft er the wind changes
direction. In the Caribbean, many anchorages are exposed to a constant
groundswell. You must use more scope to keep the anchor from breaking
out. Make sure you leave an escape path open in case of a wind shift. For
instance, with wind out of the northeast, you might choose a two-sided
headland to the north. But if the forecast calls for a wind shift to the south,
you must understand that the headland could become a dangerous lee shore. - Tides and currents. You need to know the tidal range to compute adequate
scope. Rising tides could break out an anchor with inadequate scope. Lower-
than-normal tides could increase scope to the point where the boat swings onto
a shoal or into another boat. In areas with shift ing currents, set two anchors.
Always be aware of changes in direction and strength of wind, current, waves,
and swell when at anchor. (See Chapter 12, “Weather and Water Wisdom.”) - Swinging room. Take the time to circle the anchorage and see if boats are
using one or two anchors. In areas like the Bahamas where currents shift
180 degrees, many boats anchor with two anchors. Th is cuts down their
amount of swing to about one boat length. In this case, you too would want