Seamarks
Prototype · 21 hazards · Ionian & Basque coast
In August 2026 a chartered yacht hit an unmarked reef north of Frikes, Ithaca, running both Navionics and Orca. Neither showed it. The owners said everyone local knows about that rock — and they were right, which is exactly the problem.
It is called Agriógatos. It is 50 m wide. Its position had been printed in a free online cruising guide for years.
A seamark is anything you navigate by that you can see from the water. The Spanish sailing directions say the channel past Les Briquets is passable «solo… por conocedores de las marcas» — only by those who know the marks. Then they decline to print them. This is an attempt at printing them.
The approach to Marmagkas bay. The solid track is what local boats do — south of the islet, through 235 m of clear water. The dashed one is the route that grounded: north of the islet, into a 287 m gap with the reef in it. The published guide gives the reef's coordinates and never mentions the southern approach.
The distance between the coordinates published in that cruising guide and a pin a stranger had dropped on Google Maps labelled “Attention reef”. Two free public sources had the rock. Two commercial chartplotters did not.
Seven marks, and each one is a statement about how much is actually known.
Seven of the twenty-one have coordinates their source actually published. Those get a point.
The other fourteen have no published position. Drawing a dot there would be a claim nobody made, so they get a circle of approximation instead.
Thick and solid: corroborated by more than one source. Thin and faint: one line in one forum post, unverified.
The danger is the state, not the rock. A bar that is flat at half tide and breaking on the ebb. A 16 m shoal that becomes a 15 m wave twice a decade.
Not from a chart. From someone who sails there, describing the way in.
It doesn't pass through. That is the whole point of drawing it.
Two marks in line and a rule about which side to stay. Cabo Higuer on the Biarritz light clears two reefs at once — no GPS, no chart, just your eyes.
English cruising guides quietly drop what local sailors write down. Every quote below came from a free public source, and none of it was on the plotter.
Ελληνικά
«…διότι “αναδύεται” ξαφνικά και το βυθόμετρο δεν βοηθά.»
It rises so suddenly the depth sounder does not help. No chart symbol exists for that.
Español
«…solo son abordables con buen tiempo, sin mar de fondo y por conocedores de las marcas.»
Only by those who know the marks. The guide says the marks are needed, then doesn't print them.
Français
«La vague de 8 à 15 mètres… ne déferle que rarement, pas du tout certaines années.»
The chart shows 16 metres and nothing else. On the wrong day it is a breaking wave.
English
“In the middle of the northern approach, ~250 m out, is the treacherous 50 m wide reef.”
It names the reef. It never says to use the southern approach instead.
The same 21 hazards, shown four ways. If you are not sure, take the first one.
Start here
Browse the coast A scrolling list beside a live satellite map, kept in step with each other. Filter by region, search a rock by any of its names, click anything to open it. This is the one to open if you have never seen this before. Open the browser