Rainbow's End Anchoring Downloads & RevenueRainbow's End Anchoring · App Store

The weather suddenly changes. Your boat moves around and pulls on her anchor. Do you have enough scope? Did you use the right anchor?

Rainbow's End Anchoring calculates the rode, scope, and anchor to use based on your boat, her gear aboard, the depth, the seabed, sea state, and your predicted winds. When the anchor is set, Rainbow's End Anchoring calculates the perimeter fence, and you can add a swing tolerance. Set the alarm, and if your boat drags outside the perimeter fence or swings too far, an alarm will sound aboard and for crew ashore.

We built it aboard our ketch Rainbow, for the nights the wind shifts.

THE PLAN
• Scope measured from the bow roller to the seabed, with the tide still to rise. 8 ft of water under a 6 ft bow roller needs scope on 14 ft.
• Depth corrected for how your sounder is calibrated.
• Every anchor and rode aboard is checked twice: will it set in this bottom, and how hard can it hold once it has. The best combination is recommended by the names you gave your gear.
• Five ways of lying: regular anchoring, a mooring ball, a Bahamian moor, Med mooring and lines ashore. Storm mode plans two anchors.
• The wind at which your chain pulls straight, the peak load, the swing circle, clearance under the keel at low water, and the holding margin.
• Warnings in words when the margin is thin, the anchor is wrong for the bottom, or the locker cannot support the plan.
• Feet, meters, fathoms, shots or your own rode marks. As many boats as you sail.
• Tell it how much rode you actually paid out and it draws that rode to scale — chain flat along the bottom, lifted to the anchor, or an anchor still hanging clear — and works the swing circle from your figure.

THE ANCHOR WATCH
• The fence comes from the plan, or from the rode you say you paid out: the swing circle plus a margin for GPS error, the corridor between two anchors, a tight ring for a boat held by a quay or lines ashore, the ball's reach on a mooring.
• The alarm sounds after three GPS fixes in a row clearly outside the fence, so one stray fix does not wake you. A soft chime warns first.
• Allow location “Always” and the watch runs with the phone locked. The alarm plays on the phone’s speaker, through the silent switch and Focus. If iOS stops the app, a notice says so within two minutes.
• Tighten or widen the fence after arming. It never tightens inside her swing.
• The swing alarm catches a boat that stays inside her fence but swings onto a neighbor or a shoal. Two bearings from the anchor fix the water she must not swing into, and it keeps guarding that water as she swings.
• North up or heads up, with the boat drawn to her length. Apple satellite imagery under the plot, if you switch it on.
• One word says where you stand, with the sea room left and the age of the fix.
• Mute and Disarm stay at the bottom; while the alarm sounds, Mute is on every tab.
• A night view, red on black. A wide iPad shows the plot beside the controls.

THE WATCH FROM ASHORE
• Share the watch w