Rainbow’s End Anchoring — Support

It works out how much anchor rode to pay out for the conditions you’re in, picks the best anchor-and-rode combination from the gear you actually carry, and tells you plainly what to watch — thin holding, a bottom your anchor won’t set in, not enough water under the keel at low tide. It covers regular anchoring, mooring balls, Med mooring, lines ashore, and Bahamian moors, plus a storm mode. It runs entirely offline.

Your boat, on the Boat tab: length, beam, draft, displacement, the height of your bow roller above the water, how your depth sounder is calibrated, and the ground tackle you carry — each anchor with its weight and model, each rode segment by segment. Ten minutes once, and every answer afterward is about your boat rather than a generic one.

Because it’s the most common source of anchoring error. A sounder can read from the waterline, from the transducer, or as water under the keel — three different numbers for the same anchorage. Tell the app which one yours shows and you can always type exactly what the display says; the app corrects it to true depth.

The classic ratios multiply the water depth. But your rode doesn’t start at the waterline — it starts at the bow roller, several feet up, and the tide may rise after you set. The app multiplies the full distance from bow roller to seabed at the worst point of the night. In shallow water the difference is dramatic: 8 ft of water under a 6 ft bow roller needs scope on 14 ft, nearly double what the sounder alone suggests. The old rule isn’t wrong; it just forgets where the rode begins.

It’s the estimated holding power of the recommended anchor in tonight’s bottom, divided by the estimated pull on it from wind, waves, and the boat’s yawing. Green means the margin meets what your kind of stop demands (a lunch stop needs less than leaving the boat unattended); amber means it’s thin — anchor with care and set a watch. Both sides of that ratio are estimates, which is exactly why the app insists on a margin instead of calling 1.1× good.

Setting and holding are different failures. A fluke anchor has enormous holding power in sand — and skates uselessly across a weed mat, because it never gets to use it. The app scores every anchor you carry on both questions for the bottom you chose, and when the ground is wrong for the anchor it says so instead of quietly suggesting more rode. More scope does not fix the wrong anchor.

Chain helps you by sagging: its weight keeps the pull at the anchor horizontal, which is the direction an anchor holds best. The app computes the exact wind at which tonight’s chain is pulled bar-taut and the sag is gone. Beyond that point the chain’s weight has stopped absorbing anything — which is not an emergency, it’s the moment your snubber becomes the only shock absorber, and the app tells you the pull angle so you know how much that matters.

Yes. The surge back on a gust is the moment a short rode lifts the anchor’s shank, so gusts raise the scope — the app sizes it on a figure between the sustained wind and the gusts. Peak loads (what actually parts gear) are computed at the full gust figure.

It stops recommending anchors — none of yours is in the water — and answers what is left. Your swing circle, which is smaller than at anchor because a mooring’s riser is short: about 1.5:1 for a helix ball like the BVI’s, 3:1 for chain to a block, against the 4:1 to 7:1 your own rode goes out at from the bow roller. The circle is the ball ranging on its riser at low water, plus your pennant, plus the boat. It also gives a pennant length for your bow (two and a half times its height above the water) and the pull your boat puts on the ball. What it will not do is vouch for the mooring: look for the posted rating, look at the pennant and the shackle, and back down gently to feel it hold.

Yes — as many as you like, each with its own tackle, on the Boat tab under Saved boats. Add a charter boat for the week and delete it when you fly home; keep the dinghy as its own entry. The Anchor screen always names the boat it’s calculating for, right at the top.

Yes. Rodes and anchors both take names — “Storm rode,” “Lunch hook,” “Big Mantus” — and the app uses your words everywhere it refers to them. The weight-and-model details stay visible in the boat profile, so naming loses nothing.

Always. Open “Why this anchor” and tap any combination aboard — the entire plan recalculates for what you’re actually putting down, including the warnings. The app never blocks your choice; it just refuses to pretend a poor one is a good one, and it will tell you what it would have picked instead.

Depths in feet, meters, or fathoms; rode answers in any of those plus shots (shackles) or your own rode markings at whatever interval you’ve marked. Input and output units are set separately, because you read depth off an instrument but pay out rode by your marks.

Mark the drop on the Watch tab and the app draws a fence from tonight’s plan — the swing circle plus a margin for GPS scatter when you lie to one anchor, the corridor between two anchors for a Bahamian moor, and a tight ring around a boat held by a quay or by lines ashore. It then reads the GPS and plots the boat north-up against the fence, with the trail of everywhere she has ranged. You can mark from the bow, midships, or the stern; point the phone toward the bow and the app places the anchor where it actually went down. Keep the phone plugged in with the app open on the Watch tab — the screen stays awake by itself.

By design. GPS scatters, and one wandering fix at three in the morning is not a drag. The alarm needs several consecutive fixes clearly outside the fence, beyond the fix’s own reported accuracy, so it takes a few seconds to be sure. An alarm that cries wolf gets disarmed for good, which is worse than one that takes a breath. If the GPS goes quiet or the app is closed, the screen says the watch has stopped rather than pretending to guard you.

Yes, from version 1.3.0, using a second device on the same Apple ID. Aboard, arm the watch and switch on Share to my other devices. Ashore, open the Watch tab and tap Look for a shared watch; the shore device shows the same fence, boat, and trail, and sounds its own alarm if she breaks out. The boat’s reports travel through your own iCloud and nowhere else, so both devices need to be signed into the same Apple ID with iCloud Drive on, and the boat needs a signal. Keep the app open on the shore device too — it checks for a fresh report every half minute. Only the boat can disarm the watch; silencing the alarm ashore silences it ashore only.

Yes, from version 1.5.0. Aboard, arm the watch and switch on Share with crew; the screen shows an eight-character code, with Copy, Send and New code beneath it. Anyone you give the code to opens the free companion app, Rainbow’s End Monitor, enters it, and sees the same fence, boat and trail with the same alarms — and can tap Find the boat for an arrow that points at her with the bearing and distance, which is how you get back to the right boat from a dinghy dock full of identical charter yachts. The record is encrypted with a key made from the code; nobody without the code can read it, and it is deleted when you disarm or switch sharing off. The code stays until you choose New code. Crew can watch and find; only the boat can disarm.

Not necessarily — but the app refuses to guess. If no report has arrived for a minute and a half the screen says the link is stale; after three minutes of silence the monitor sounds an alarm, because a dead link must never look like a safe boat. Silence usually means the boat lost her signal, the phone aboard died or went to sleep, or the app was closed. The watch aboard may well still be running; the alarm is telling you to find out, not that she has dragged. The one silence that is expected is a watch the boat disarmed itself, which the shore device reports in those words and then goes quiet without alarming.

Not for the calculator: Rainbow’s End Anchoring works entirely offline and nothing you enter leaves your device. The anchor watch asks for location permission, “while using the app” only, and reads the GPS — which is satellites, not internet — on the device alone. The remote watch and sharing with crew are the features that need a connection: switch on “Share to my other devices” and the watch, and only the watch, is copied to your own iCloud so your other devices can monitor it; switch on “Share with crew” and it is published encrypted under a code for the people you give the code to. Both off by default, readable by nobody else. See the privacy policy, which is still short because there is still little to disclose.

No, and be wary of any anchoring tool that claims otherwise. Holding power varies between anchorages and between one set and the next in the same spot; the coefficients in the app are estimates drawn from independent testing, not manufacturer claims. The app is an aid to judgment — if its answer disagrees with your seamanship, trust your seamanship.

Please tell me — seriously. Every calculation in this app got better because a sailor said “that doesn’t look right” and included their inputs. Email the numbers you entered, what the app said, and what you expected, and I’ll trace it through the math and either fix the app or show the working.

Purchases are handled by Apple and Google, so refunds are too — through reportaproblem.apple.com for the App Store, or your order history on Google Play. I never see your payment details and can’t issue refunds directly.