Anchor Rode Scope and Swing Radius
The bow-height-and-high-tide scope that keeps an anchor set: scope is rode paid out over the VERTICAL rise from the seabed to the bow roller -- depth PLUS bow-roller height, at HIGH tide, not the sounder depth. In 15 ft of water with a 3 ft bow roller the true vertical is 18 ft, so a 7:1 scope needs 126 ft of rode (a 154.7 ft swing radius for a 30 ft boat); anchoring on 15 ft alone pays out only 105 ft = an actual 5.8:1, the quiet error that drags at 2 a.m. All-chain holds at 3:1 (54 ft rode, an 80.9 ft swing) -- a tighter circle, why it is favored in a crowded anchorage. A planning aid; conditions, bottom type, and skipper judgment govern.
Formula and source
vertical = depth + bow_height (at high tide); rode = scope x vertical; actual_scope = rode / vertical; swing_radius = sqrt(rode^2 - vertical^2) + boat_length.
Anchor rode scope and swing-radius relations (seamanship convention -- Chapman Piloting, US Sailing, ABYC ground-tackle references), by name; local conditions, bottom type, and skipper judgment govern.
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