Anchor Check
Know your night before you sleep on it
Every forecast app can tell you the anchorage is tenable at sunset. None of them answer the question that keeps you in the cockpit: what does 2 a.m. look like? Anchor Check scores the next 48 hours against your specific anchorage, hour by hour, and hands you a verdict you can set an alarm by.
An anchor alarm wakes you after you drag. This tells you before.
The night after a passage is the hardest sleep in cruising. You made landfall, the hook is down, and now every gust and every new roll of the boat asks the same question: is this the one? So you wake every twenty minutes and squint at the shoreline, or you sit an anchor watch you are too tired to keep.
The information you actually need exists at sunset. The forecast already knows the breeze will veer southwest at 02:00, that it will blow 22 gusting 28 straight into the one sector your cove is open to, that the chop will follow it in and the bow will start to slap, and that by 04:00 it is easing. What no app did until now is read that forecast the way an anchor watch would: against your anchorage, your exposure, your ground tackle.
Anchor Check gives you the bad hour in advance. A clean night gets said out loud too: no alerts in the next 48 hours. That single sentence is what finally lets you go below.
How it works
1. Drop the pin
Tap the anchor button on the map and drop a pin where the hook is set. The point forecast for that spot is fetched from the model you are viewing, run and model named on the result.
2. The chart fills in your exposure
The compass fills itself from the charted coastline: which sectors are open, with the miles of fetch each one carries. Tap any sector to override what the chart cannot know, then set the wind and gust you trust your tackle to hold. Overrides and thresholds are saved for the 2 a.m. re-check.
3. Read the night
The next 48 hours are scored hour by hour: green when nothing blows into your open sectors, amber as wind — or the chop it builds across your fetch — approaches your limits, red when it crosses them. Plus the sentence that matters: when it starts and how long it holds.
The verdict, not a graph
A wind graph makes you do the work at midnight. Anchor Check does the reading and reports like a crew member: which sector, how strong, starting when, lasting how long. The example on the right is the real output format.
Peace of mind is one half. Comfort is the other: ten degrees of wind shift is the difference between a flat night and rolling in wind chop until dawn. The scoring knows how much sea the wind can actually build, because every open sector carries its charted fetch — and when long-period swell is running offshore of an open sector, a separate warning says so. Seeing it coming while there is still light means you can reset the hook, rig a bridle, or take the next cove over, on your schedule instead of the weather's.
⚓ Rock Sound, Eleuthera Open to: W · SW · S — auto from chart W 3.1 nm · SW 25+ nm · S 7.4 nm ⚠ SW 22 kt gusting 28, building ~0.9 m chop into your open sector from 02:00 for ~2 h 21:00 ✓ 22:00 ✓ 23:00 ✓ 00:00 ✓ 01:00 ⚠ 02:00 ✗ 03:00 ✗ 04:00 ⚠ 05:00 ✓ 06:00 ✓ GFS 06z · charted depth 4.9 m alert ≥ 15 kt wind / 20 kt gust
What it does not do
Honest limitations
- It is not an anchor alarm and does not watch your GPS position. Keep your alarm set; this tool decides when the alarm actually needs your attention.
- The swell-wrap warning is an estimate, not physics. It samples the offshore wave forecast beyond your open sectors and applies a period-scaled wrap allowance; it does not model refraction or diffraction around your specific headland. Treat it as a reason to look, not a wave height to plan on.
- Computed exposure is only as good as the chart. A dock, a breakwater, or a reef that breaks the swell may be smaller than the coastline data can see. Your eyes outrank the compass — tap a sector to override, and the override wins.
- It samples the nearest forecast grid point and discloses the offset in coarse offshore cells. A 25 km global model cell cannot see katabatic acceleration off a specific cliff, and terrain effects are not modeled.
- It does not know your scope, holding, or bottom, and it does not model current. You set the thresholds; it reads the forecast against them.
Frequently asked questions
Is Anchor Check an anchor alarm?
No, and you should keep using one. An anchor alarm wakes you after the boat has already moved. Anchor Check reads the forecast before you turn in and tells you which hour of the night carries the risk, so you can set one deliberate alarm for 01:45 instead of being woken at 02:30 by a GPS fence. They solve different halves of the same night. Use both.
What data does the verdict come from?
Four sources, each named on the result. The point forecast of the weather model you have active on the map scores the wind. The charted coastline — the same high-resolution land data the routing engine trusts — computes which sectors are open and the fetch across each. GEBCO bathymetry supplies the charted depth at your pin. And the Copernicus wave model is sampled offshore of your open sectors for the swell check. The app tells you when any of them is unavailable rather than quietly inventing it.
Does it know my swinging room, holding, or bottom type?
Holding, scope, and bottom type: no, and it does not pretend to. Exposure: yes. Drop the pin and the compass fills itself from the charted coastline — which sectors are open, and how many miles of fetch each one carries. Your local knowledge still outranks the chart: tap any sector to override, and your override governs everything — wind scoring and the swell check alike. Overrides are remembered for that anchorage; a different anchorage always starts from its own chart, never from a previous cove's settings.
Does it work in remote anchorages?
Anywhere the global models cover, which is effectively anywhere you can float. In coarse offshore grid cells the app discloses that the nearest forecast point may sit a few kilometers from your pin rather than presenting it as exact.
Do my sectors and thresholds survive closing the app?
Yes. They persist on your device, so the 2 a.m. re-check is one tap on the anchor button, not a re-briefing of your own anchorage.
Does it forecast swell into the anchorage?
It estimates two kinds of sea state, and labels both as estimates. Wind chop is computed from each open sector's charted fetch — 20 knots across eight miles of sound builds a very different night than 20 knots across a quarter-mile lagoon — and the estimate escalates the verdict on its own. For long-period swell, it samples the offshore wave forecast beyond every fully open sector you leave exposed and warns when swell could reach or wrap into the anchorage, with a wider allowance for longer periods because long swell bends around headlands. A qualifying swell warning caps the overall verdict at watch — you will never see a green tenable verdict above a swell warning — and if wave data is missing for any open sector, the verdict says the coverage is partial instead of pretending it checked. What it does not do is model refraction around your specific headland; the warning is a reason to look, not a wave height to plan on.
Is Anchor Check free?
It is live on the map today for signed-in users on the free tier. Drop the anchor pin, let the chart fill in your exposure, read your night.
Keep exploring
Tonight has a forecast. Read it before you sleep on it.
Anchor Check is live on the map for free-tier accounts. Drop the pin, let the chart mark your sectors, set one alarm instead of five.
Score tonight's anchorage