Colour
visible
Leaves on its own: 1 of 4
This mark: red, plain
Each of the four patterns has a different colour: red, green, vertical red-and-white stripes, horizontal black-and-red stripes.
IALA A system · four patterns · a diagram, not for navigation
A mark without one feature
A buoy speaks through three features at once: colour, body and topmark. Hide one, two or all of them and check which of the four patterns still fit what you can see.
Without JavaScript you see one state of the mark (left side of the channel, all features visible). The hiding toggles need JavaScript; the comparison, the three observations and the catalogue below work without it.
Left side of the channel. Colour: red, plain. Body: cylindrical. Topmark: red cylinder.
Grey = hidden colour. Dashed outline = hidden topmark. Neutral pillar = hidden body. Original drawing, a diagram: not a map, not a measurement, not for navigation. Limits of the model · Sources
What still fits what you can see
1 of 4 matching patterns
All features visible: one matching pattern — Left side of the channel. This is a match within a set of four patterns, not the identification of an object in the field.
Visible: colour, body, topmark. Hidden: nothing.
Four patterns · choose the one you are viewing
How much each feature settles on its own · for the mark: Left side of the channel
Body
visible
Leaves on its own: 1 of 4
This mark: cylindrical
This shape occurs in only one of the four patterns.
Topmark
visible
Leaves on its own: 1 of 4
This mark: red cylinder
Each of the four patterns has a different topmark: cylinder, cone, one sphere or two spheres.
“Leaves on its own” counts how many of the four patterns this one feature would not exclude if it were the only one visible. A rule-based model, not a measurement.
Comparison
Two similar pillars, two differences
Safe water and isolated danger share a silhouette: a pillar body, stripes, spheres on top. They differ in the direction of the stripes and the number of spheres. Below are all four conditions at once, at the same scale, without a toggle.
- A — safe water: vertical red-and-white stripes, one red sphere.
- B — isolated danger: black with a horizontal red band, two black spheres.
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1 · Everything visible
A B Two independent differences: the direction of the stripes and the number of spheres. Both point the same way.
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2 · Colour hidden
A B What remains is the number of spheres: one or two. It works only when the topmark is fitted and visible.
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3 · Topmark hidden
A B What remains is the arrangement of the stripes: vertical or horizontal. It works only when the stripes are clearly visible.
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4 · Colour and topmark hidden
A B Two identical grey pillars. Nothing tells A from B, yet they mean different things. “I don’t know” is the only honest answer here.
This is an exercise in features, not guidance on where it is safe to sail.
Incomplete observation
Three situations in which something fails
Instead of eight tasks with points: three observations, each showing the meaning of a different feature and ending with what is still uncertain. No score, nothing saved. Observations 1 and 3 follow the same rules as the toggles above (in the tool, observation 1 corresponds to a hidden colour and body, because a pillar body excludes nothing and gives the same result as a hidden one; observation 3 corresponds to all three features hidden). Observation 2 shows partial visibility of the colour (stripes of unknown direction), which the toggles do not model.
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Diagram of observation 1 1 · Against the sun: the topmark is visible
- What you see
- A dark silhouette, a pillar body, a cone on top with its point up. The colour is not visible.
- Matching patterns
- 1 of 4: right side of the channel. The cone is the topmark of only one of the four patterns; a pillar body excludes nothing.
- Excluded
- Left side of the channel (cylinder), safe water (one sphere), isolated danger (two spheres).
- Still uncertain
- The result holds only within the set of four patterns; a cone is also the topmark of marks outside this set (to be checked in R1001). “Right side” depends on the direction of buoyage, which a silhouette does not show.
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Diagram of observation 2 (stripe direction is conventional) 2 · Fog at close range: stripes without a topmark
- What you see
- A pillar body striped in two colours; the direction of the stripes is indistinct. The topmark is not visible.
- Matching patterns
- 2 of 4: safe water and isolated danger. This is an example in which more than one pattern fits.
- Excluded
- Left and right side of the channel: they have plain colours.
- Still uncertain
- Vertical or horizontal stripes: exactly the information that is missing, and these two marks mean different things. The absence of a topmark settles nothing, because a topmark may not be fitted (to be checked in R1001). The page does not suggest what to do on the water.
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Diagram of observation 3 3 · A bare pillar
- What you see
- A pillar body with no colour and no visible topmark: a silhouette or a shape blending into the background.
- Matching patterns
- 4 of 4: each of the four patterns can look like this.
- Excluded
- None.
- Still uncertain
- Everything. “I don’t know” is the correct and complete answer here: nothing in this set tips the balance. Narrowing the result would take one additional feature (a cylindrical shape, a cone on top, a colour).
Explanation and limits
What this model does and what it does not
Rules (assumptions of the model, not quotations from standards)
- Colour is the colour and arrangement of stripes of the whole mark, including the topmark. Each pattern has a different one: red, green, vertical red-and-white stripes, horizontal black-and-red stripes. In the tool, colour is a binary feature: fully visible or fully hidden. Partial visibility (e.g. stripes of unknown direction) is shown only in the description of observation 2; the toggles do not model it.
- Topmark: cylinder, cone, one sphere, two spheres. A pattern is excluded when the visible topmark is different. The absence of a topmark excludes nothing.
- Body: cylindrical occurs only in the left side of the channel, conical only in the right, spherical only in safe water. Pillar and spar fit all four.
- A hidden feature excludes nothing. Unknown is not zero and not “absent”.
What the model does not do
- It does not identify real objects. The four patterns are a closed set; other families of marks also occur on the water (e.g. cardinal, special; the list is to be checked in R1001), and the rule “one feature is enough” works only within this set.
- It is not navigation: it does not show where to sail and does not describe the current marking of any channel on the Lagoon.
- The drawings are original diagrams: proportions, shades and the number of stripes are conventional. They do not show the direction of buoyage or real lighting.
- It is a rule-based model, not a study of how marks look in specific visibility conditions.
Compared with the previous version
Removed: the eight-task quiz with points and progress saved in the browser, the “100% certainty” indicator, the tabs, the photo embedded from an external server and the button that clears memory. Nothing is saved, so there is nothing to delete.
The four patterns in text
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Left side of the channel · lateral mark, Region A
- Colour
- red
- Body
- cylindrical, pillar or spar
- Topmark
- red cylinder, if present
Marks the left edge of the channel, looking in the direction of buoyage.
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Right side of the channel · lateral mark, Region A
- Colour
- green
- Body
- conical, pillar or spar
- Topmark
- green cone, point up
Marks the right edge of the channel, looking in the direction of buoyage.
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Safe water · safe water mark
- Colour
- vertical red-and-white stripes
- Body
- spherical, pillar or spar
- Topmark
- one red sphere, if present
In the definition of the system it indicates navigable water around the mark. It does not denote an obstruction.
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Isolated danger · danger mark
- Colour
- black with horizontal red bands (one band in the drawing)
- Body
- usually pillar or spar
- Topmark
- two black spheres, one above the other
Marks an isolated danger around which the water is navigable.
Descriptions carried over from the previous version of the page. Whether the topmark is mandatory or optional for each pattern needs to be checked in R1001; the model assumes that its absence excludes nothing.
Context and sources
The Lagoon is the context, the symbols are the lesson
In changing light, marks are recognised through the interplay of colour, body and topmark. This page does not point to any specific mark on any specific channel and does not describe the current marking. Version V3 assembled on 11 October 2026 from V2 material; the facts have not been re-checked against the sources.
Sources of the lesson on marks
- IALA, R1001 “The IALA Maritime Buoyage System”, edition 2.0 — lateral marks of Region A (2.1.3), isolated danger (2.3), safe water (2.4), direction of buoyage. To be checked: the address and section numbers come from the previous version and were not opened when V3 was built.
- Rozporządzenie z 4 grudnia 2012 r., Dz.U. 2013 poz. 57 [Regulation of 4 December 2012, Journal of Laws 2013, item 57] — § 4 and part A of the annex: Polish names, meaning, colours and shapes. To be checked: the date of the act comes from the previous version; whether the text is current (amendments, consolidated version) has not been checked, and the state of marking on the Lagoon is not assessed.
- Contextual photograph not embedded (the page works offline): Vistula Lagoon, 2015, Alan Szmyt, Wikimedia Commons, licence as in the previous version: CC BY-SA 3.0 PL. To be checked: authorship and licence were not verified in this version.
Disclaimer: a closed educational model. Decisions on the water are made solely on the basis of official nautical charts, pilot books and notices.