A Rethymno boat trip is a sea outing from the north coast of Crete, starting at the harbour of Rethymno town. The trip is one of the Greece Tours on Greece Ville.
This post covers the setting in numbers, the Venetian harbour, the seabed, currents, sea temperature, knots, the Beaufort scale, life jackets, seasickness, sun, seabirds, navigation and common questions.
What is a Rethymno boat trip?
A Rethymno boat trip starts at Rethymno, a port on the south shore of the Sea of Crete. The town community of Rethymno had 35,763 residents at the 2021 census. The town community covers only 26.777 square kilometres in total.
On a Rethymno boat trip, the port town lies in the municipal unit of Rethymno. That unit had 38,759 residents at the 2021 census. It covers 126.5 square kilometres in all.
Violi Charaki is the second largest settlement of the regional unit. It counted 3,185 people in the 2021 census. Rethymno city had 11,057 people in 1951 and 28,987 people in 2001.
For a Rethymno boat trip, the regional unit around the port is shaped by mountains. About 65% of it is mountainous, 19% is semi-mountainous and 16% is flat. Semi-mountainous means land partly hilly.
Mount Kedros rises in the Rethymno regional unit. It is conical, which means shaped like a cone, and made of limestone. Its topographic prominence, the height above nearby land, is 1,300 metres.
- Amari: Amari is a mountain municipality of the Rethymno regional unit and covers 277.285 square kilometres.
- Mylopotamos: Mylopotamos municipality covers 360.703 square kilometres and had 14,363 inhabitants at the 2021 census.
- Agios Vasileios: Its main office is in the village of Spili, and it had 7,018 residents in 2021.
Crete was an autonomous state when the Rethymno prefecture was created. The prefecture stayed after Crete joined Greece in 1913.
How was the Venetian harbour built for a Rethymno boat trip?
A Rethymno boat trip is tied to the old harbour that the Venetians built. They used large, well-cut stones taken from the local area. Big earthquakes that damaged the town also hurt the harbour, says a local history of the port.
On a Rethymno boat trip, the harbour’s mole is the stone wall that shields the water. In 1618 the eastern mole was thoroughly rebuilt, and builders also tried to make a southern quay.
In 1630 a counter-breakwater, a wall against waves, was built in the middle of the harbour. A local writer says an opening under the mole made a current that cleared sand.
On a Rethymno boat trip, the entrance has a story. One source says a new port was judged too costly. So a three-masted ship loaded with stones was sunk at the entrance.
The same source says the fix did not last, and a canal had to be dug in 1882. The old harbour was too shallow for large merchant ships of its day.
- Cargo: Shallow water kept ships off the mole in the early 1900s, so small boats carried cargo.
- Lighthouse: Egypt’s harbour works on Crete included the lighthouse, as part of rebuilding the island.
- Storms: Northwest gales wore away the protective armour of the windward mole, the wall facing the wind.
A project repaired the floor at the foot of the windward mole. Earlier storms had damaged that floor.
Which seabed lies under a Rethymno boat trip?
A Rethymno boat trip happens around Crete, where the sea floor is anything but flat. Deep basins of the western Hellenic Trench reach depths over 4000 m. Undersea ridges and mountains also rise from the floor around the island.
On a Rethymno boat trip, the Ptolemy Trench is the deep water south of central Crete. It is 2500-3700 m deep and ends at the Ierapetra graben, a long sunken strip of crust.
The Pliny Trench, one of three eastern branches of the Hellenic Trench, is 3700-4500 m deep. The Strabo Trench is 3000-3500 m deep and divides Aegean crust from the Mediterranean Ridge.
On a Rethymno boat trip, the Balos Ridge is a 20 km undersea ridge north of Crete. Its summit lies only 78 m below the surface, much shallower than the trenches.
The Elafonissi seamount, an underwater mountain, continues the mountains of south-western Crete, with its top 994 m down. The Faistos and Knossos seamounts carry Minoan site names, and Knossos has two peaks.
- Mud volcanoes: Fields of mud volcanoes, which are vents that push out mud, sit on the Mediterranean Ridge.
- Knossos peaks: The Knossos seamount has two peaks, found 388 m and 651 m below the surface.
- Dark mud: Layers called sapropels, rich in organic matter, formed in the Mediterranean about every 21,000 years.
The last sapropel formed 9.5 to 5.5 thousand years ago. The Aegean plate moves south at about 33 mm a year.
Which currents move past a Rethymno boat trip?
A Rethymno boat trip takes place in the eastern Mediterranean, where surface water moves in large circles. Four large anticyclonic gyres, which are wide circling currents, dominate the surface circulation there. They are named Pelops, Ierapetra, Mersa-Matruh and Cyprus.
On a Rethymno boat trip, Atlantic water in the east forms a layer 100 to 200 metres thick. This layer flows anticlockwise along the continental slope, the steep edge of the sea floor.
The Cilician and Asia Minor Currents continue that flow. The Asia Minor flow enters the Aegean, mostly in winter. Otherwise it turns southwest to feed the Ierapetra eddy, a circling patch of water.
During a Rethymno boat trip, the largest eddies are circling patches of water that last months or years. An Ierapetra eddy can stay in one place for more than a year.
The Pelops Gyre reaches about 800 to 900 metres below the surface. Satellite data gave Pelops top surface speeds from under 10 to over 20 centimetres a second. Speeds varied across the years studied.
- Drift: An Ierapetra eddy can also drift hundreds of kilometres and merge with an older one.
- Gibraltar: Through the Strait of Gibraltar, deeper, saltier water flows west while fresher surface water flows east.
- Slow renewal: Water stays in the Mediterranean for about 100 years, so the sea renews itself slowly.
The Cyprus Gyre is about 80 to 100 kilometres wide and tops out at 50 centimetres a second.
How warm is the sea on a Rethymno boat trip?
A Rethymno boat trip happens on the Cretan Sea, and its water warms in summer. In July, the water above 50 m deep reached 20 °C at the Cretan Sea buoy. It stayed near that value until the end of October.
On a Rethymno boat trip, the sea has layers with different temperatures. At the Cretan Sea buoy, the water 40 m down was coldest in March and warmest in October.
A thermocline is a layer where temperature changes fast with depth. The seasonal thermocline lay between 40 and 65 m deep. At 90 m and 150 m the buoy showed no significant seasonal change.
For a Rethymno boat trip, the layers of water at the buoy change with the seasons. From November, the thermocline slowly mixed into deeper water, and it vanished in early January.
During February 2001, winter mixing at the buoy reached only 100 m. In March 2000, the water column was evenly mixed. It went from 14.5 °C at 500 m to 15.5 °C at 150 m.
- Salt: In summer, the salinity of the Cretan Sea’s surface layer, meaning its saltiness, rose above 39.3.
- Sinking: In September and October, as the thermocline fades, this salty water sinks to about 80 m.
- Surface: Studies found monthly average surface temperatures in the southern Aegean peaked at 26 °C in summer.
Satellite maps of the Aegean show its highest surface temperatures over the Cretan Sea, not near the Dardanelles.
How do knots and nautical miles measure a Rethymno boat trip?
A Rethymno boat trip is measured in nautical miles and knots. The international nautical mile is 1,852 metres. Britain adopted it in 1970, after using an Admiralty mile of 6,080 feet. The land mile is exactly 1.609344 kilometres, set by a 1959 agreement.
On a Rethymno boat trip, distance is counted in nautical miles, not in land miles. The word mile comes from the Roman phrase mille passus, which means a thousand paces.
The metre was first defined from the size of Earth. It was one ten-millionth of the distance from the North Pole to the equator. So Earth measures about 40,000 km around.
For a Rethymno boat trip, the nautical mile is key. The geographical mile is one minute of arc along the equator. It is about 1,855.3 metres, a little longer than the nautical mile.
A chip log was a quarter-circle board of wood, weighted with lead along its bottom. It acted as a drogue, a drag staying roughly in place as the ship sailed away.
- Dutchman’s log: Credited to Portuguese Bartolomeu Crescêncio, it timed a floating object between two points on deck.
- Log line: One common spacing was 8 fathoms, or 14.6 metres, between knots in the log line.
- Taffrail log: It tows a rotor on a long line from the stern, like a car’s odometer.
At hull speed, bow and stern waves reinforce each other, making big waves and large wave drag.
How does the Beaufort scale describe the sea on a Rethymno boat trip?
A Rethymno boat trip happens on the sea, and the Beaufort scale describes how rough that sea is. Before Beaufort, naval weather notes were subjective, which means they were based on personal opinion. One officer’s “stiff breeze” can be another’s “soft breeze”.
On a Rethymno boat trip, wind and waves matter, and Francis Beaufort gave them a scale. He served as Hydrographer of the Navy, the post for sea charts, from 1829 to 1855.
In 1811 and 1812, Beaufort charted the south coast of Anatolia, which he called Karamania. In 1833, he published the first Admiralty Tide Tables, which list the rise and fall of the sea.
Beyond a Rethymno boat trip, the scale has a wider story. Beaufort persuaded the Board of Trade to set up a Meteorological Department, a weather office. Robert FitzRoy became its first director.
In the late 1830s, the Royal Navy made the scale a standard for ship’s log entries. A log is a written record. George Simpson, director of the UK Meteorological Office, added the land-based descriptions.
- Force 5: A large number of white horses, meaning foamy wave tops, form, and spray is possible.
- Force 8: The edges of the wave crests begin to break into spindrift, which is blown spray.
- Force 11: Small and medium-sized ships can vanish behind the waves for a long time.
The names “storm” and “hurricane” on the scale describe wind strength only, not a thunderstorm or tropical cyclone.
How do life jackets and rescue gear protect a Rethymno boat trip?
A Rethymno boat trip depends on gear that works in an emergency. Lifejackets keep a person afloat, and beacons send out a distress signal. Radar transponders help rescuers find a boat. Each item has a clear job at sea.
On a Rethymno boat trip, a lifejacket only helps if it works. Lifejacket clinics inspected jackets that people brought in. They found that 30% of those jackets failed to work in an emergency.
A screw-in CO2 bottle that has worked loose is a common cause of lifejacket failure. A 275N lifejacket is built to float the wearer with mouth and nose clear of the water.
On a Rethymno boat trip, cold shock strikes the moment a person enters the water. British fishing rules therefore refuse belt-type lifejackets that need a second step to put them on.
A beacon sends a distress signal. One with GPS broadcasts its position to within 100 m in the usual case. Older beacons without GPS place a boat only within 2 km.
- Release: A hydrostatic release frees the beacon when the boat sinks to a set depth.
- Radar: A rescue radar transponder, or SART, answers only 9 GHz X-band radar, not S-band.
- Signal: A 406 MHz beacon sends its distress signal every 50 seconds, shifted slightly over 2.5 seconds.
Rescuers close in on a beacon using its 121.5 MHz homing signal. Newer beacons also give the AIS location signal.
How do the inner ear and eyes cause seasickness on a Rethymno boat trip?
A Rethymno boat trip moves the body in ways the inner ear and eyes sense differently. The inner ear detects motion and gravity. The eyes track the world. Clashing signals from these senses are blamed for seasickness on the water.
When the head turns on a Rethymno boat trip, fluid in the inner ear moves. This fluid, endolymph, is about as dense and as thick as water. Moving fluid pushes a jelly-like cupula.
Hair cells inside the cupula turn that push into electrical signals. Tiny calcium carbonate granules called otoconia weigh down the otolith membrane. This makes the membrane react strongly to gravity and motion.
During a Rethymno boat trip, a tilting head makes the otolith membrane sag. The sag bends the hair cell cilia, which stimulates the cells. The brain must separate gravity from boat movement.
The vestibulo-ocular reflex moves the eyes less than 10 milliseconds after the head moves. This quick reflex uses only three neurons. One theory says eye-muscle stretch stimulates the vagus nerve and causes sickness.
- Theory: In 1975, Reason and Brand blamed a clash between sight, balance and body-sense signals.
- Wave rhythm: A medical review calls slow up-and-down motion the main seasickness trigger, strongest near 0.16 Hz.
- Small boats: Waves make a small boat move up and down, and also pitch and roll.
In a lab test, all 12 highly susceptible volunteers felt moderate nausea at 0.2 Hz. At 0.1 Hz, 8 felt it.
How does sunlight burn skin on a Rethymno boat trip?
A Rethymno boat trip exposes skin to sunlight from above, from the water and from the deck. Ultraviolet light, or UV, is the part of sunlight that burns skin. The sky scatters it, so shade does not give full protection.
On a Rethymno boat trip, the global UV index shows how strong the sunlight is on any day. Green means 0-2, yellow 3-5, orange 6-7, red 8-10, and violet 11 and above.
UVA covers 315 to 400 nanometres, and UVB covers 280 to 315 nanometres. A nanometre is a tiny unit of length. The atmosphere blocks about 77% of UV when the Sun is highest.
During a Rethymno boat trip, UVA burns less than UVB, because it carries less energy. UVA goes deeper into skin and ages it with little redness. So its dose is easy to underestimate.
UV is strongest with the Sun overhead, because its rays take the shortest path through the atmosphere. Near noon, more UV arrives straight from the Sun. Morning and evening bring more scattered UV.
- Reflection: Dry sand reflects 15-18% of UV, wet sand about 7%, and a boat deck 7-9%.
- Water: At half a metre under water, UV is still 40% as intense as at the surface.
- Glass: A cabin window passes about 90% of light above 350 nanometres, so UVA still comes through.
A shadow shorter than the person means higher UV. The first signs of sunburn can take hours to appear.
Which seabirds fly over a Rethymno boat trip?
A Rethymno boat trip is a chance to learn about seabirds. Scopoli’s shearwater is 45 to 52 cm long. Eleonora’s falcon has long pointed wings and a long tail. Audouin’s gull shows little tendency to wander away from its breeding areas.
On a Rethymno boat trip, Scopoli’s shearwater is one seabird to know. Besides small fish, it eats cephalopods, which are squid-like animals, and crustaceans. It only rarely plunges completely beneath the surface.
Scopoli’s shearwater also forms large colonies on the island of Linosa and on the Balearic Islands. The Italian naturalist Giuseppe Acerbi described the yelkouan shearwater in 1827. He used specimens from Turkey’s Bosphorus.
During a Rethymno boat trip, Eleonora’s falcon is a bird to watch. It looks like a large Eurasian hobby or a small slender peregrine. Its call is “kek-kek-kek”.
Tilos in the Dodecanese holds 650 pairs of Eleonora’s falcons, about 10% of the world population. The falcon eats large insects such as dragonflies in flight, passing them from its claws to its beak.
- Audouin’s gull: This seabird gets its name from the French naturalist Jean Victoire Audouin.
- Shag dive: Before a dive, a European shag jumps out of the water first for push.
- Tail count: The European shag’s tail has 12 feathers, while the great cormorant’s tail has 14.
Seabirds that soar dynamically fly zigzag half circles. They climb into the wind and dive back downwind to gain airspeed.
How do captains navigate near a Rethymno boat trip?
A Rethymno boat trip sails on waters where captains use satellites, ship radio and radar. GPS gives the position and AIS, a ship radio system, shows nearby ships. Radar stays the main tool against collisions. Official paper charts add to these tools.
On a Rethymno boat trip, a GPS receiver reads signals from 24 to 32 satellites. The satellites sit in six orbit planes tilted about 55 degrees. At least six are always in view.
Receivers that use the L5 signal reach an accuracy of about 30 centimeters. Differential GPS uses fixed ground stations to correct errors. It can improve accuracy from about 15 metres to 1–3 centimetres.
On a Rethymno boat trip, AIS lets ships share data by radio. Each AIS radio channel has 2,250 time slots every 60 seconds. Ships take turns instead of talking over each other.
Radar finds objects by itself, but AIS relies on data other ships send. Marine S-band radar copes better with rain and waves. X-band radar shows finer detail in clear weather.
- Orbit: Each GPS satellite circles the Earth in about 11 hours and 58 minutes.
- Corrections: EGNOS uses 40 ground stations and 3 satellites to make GPS positions more reliable.
- Charts: The Greek set of paper charts holds 184 charts in different scales covering all Greek territory.
Sea survey crews record shipwrecks, submarine cables, buoys and beacons. This keeps the official Greek charts correct.
What do visitors ask about a Rethymno boat trip?
A Rethymno boat trip raises questions about stings, cramps, thirst, glare and rolling. Hot showers ease jellyfish pain. A 1968 test found no cramps after swimmers ate. Seawater makes the body lose more water than it takes in.
What helps after a jellyfish sting on a Rethymno boat trip?
A European review says a hot shower eases jellyfish pain and deactivates venom. The water stays between 42 °C and 45 °C. The main symptoms are intense pain and an itchy rash. Nets cut Mediterranean stings by 90%.
What about sea urchin and weever fish stings on a Rethymno boat trip?
A bluish mark can help show a sea urchin spine. After spine removal, pain beyond 5 to 7 days points to infection or leftover spine. Folk cures for weever fish stings have limited or no value.
Does swimming after eating cause cramps on a Rethymno boat trip?
In 1968, 24 swimmers ate cereal, toast and milk, waited different times, then swam laps. None had cramps or nausea. For a calf cramp, lifting the toes toward the shin stretches the muscle and gives quick relief.
Why does dehydration happen on a Rethymno boat trip?
Seawater is saltier than urine, so the kidneys make extra urine to clear the salt. More water is lost than drunk. Plain water restores only the blood plasma volume, which switches off thirst before the body’s salts are replaced.
Why does glare matter on a Rethymno boat trip?
Disability glare impairs the sight of objects without necessarily causing discomfort. When the sky reflects in a lake, glare hides the bottom and objects. Two polarising lenses block all light when stacked with one turned 90°.
Why does a boat roll on a Rethymno boat trip?
Swells are less random in shape than wind waves. A wave group holds about seven waves in a storm, but 20 or more in distant swells. A roll tilts a boat side to side around its long axis.