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Crow Sound to St Mary's Pool (Scilly)

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What is the route?
Saint Mary's Road, at the heart of the Isles of Scilly, may be approached from seaward through five entrances, Saint Mary's Sound, Broad Sound, North West Passage (formerly known as the 'North Channel'), Smith Sound and this entrance the tidal Crow Sound. It is an alternative to the generally recommended St Mary's Sound to St Mary's Pool Route location approach to St Mary's Road for vessels approaching the island group from the east and northeast. The Crow Sound route lies to the northeast of St Mary’s, between it and the Eastern Isles and St Martin.

Crow Sound
Image: Visit Isles of Scilly

The route requires a rise of the tide to pass over Crow Bar, a shallow bank that separates Crow Sound from St. Mary’s Road, that has the least depth of 0.4 metres LAT through its channels along this passage. The use of this entrance route must, therefore, be timed for a sufficient rise of tide to clear the bar. Crow Sound is not recommended after dark because it has no lit markers and it requires eyeball navigation to identify any potentially shifting sands.

Why sail this route?
The primary advantage of Crow Sound is it provides an approach that is sheltered from the prevailing west and southwest winds. Given suitable weather and state of the tide, in an excellent alternate approach to St Mary's Road and when it is available the island a passenger ship, RMV Scillonian III, takes this route.

Tidal overview
Today's summary tidal overview for this route as of Friday, April 12th at 11:53. The principal focus of this route is to secure a sufficient rise of tide to pass through the Bar Channel with the streams being secondary. We provide tidal streams here for convenience. The northeast going stream along the southern coast of St. Mary's turns northward into Crow sound after 0145 Devonport (+ 0500 Dover). Off Watermill Cove the northwest-going stream, spring rate 0.9 knots, begins +0430 Devonport (-0110 Dover) and runs for 3 hours only. The east by southeast going stream, spring rate 0.9 knots, begins -0455 Devonport (+0150 Dover) and runs till -0100 Devonport (+0545 Dover). The stream is then slack, for a short period, after which it again runs east by southeastward, spring rate 0.7 knots, till +0430 Devonport (-0110 Dover). Between Hats and Crow Bar the stream is irregular and weak, with a rate which does not exceed 0.5 knots at springs.

Within Crow Sound the streams are much weaker, rarely exceeding 1 knot at springs, running (NW) into the Sound for 3 hours from HA HW Dover -0100, then out of the sound (ESE) for eight hours, beginning HW Dover +0200.

Southeast going stream

(HW Dover +0150 to +0545)

Starts in 04:18:25

(Fri 16:12 to 20:07)

Northwest-going stream

(HW Dover -0110 to +0150)

Starts in 01:18:25

(Fri 13:12 to 16:12)

What are the navigational notes?
Please use our integrated Navionics chart to appraise the route. Navionics charts feature in premier plotters from B&G, Raymarine, Magellan and are also available on tablets. Clicking the 'Expand to Fullscreen' icon opens a larger viewing area in a new tab.

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The above plots are not precise and are indicative only.


Crow Sound lying to the northeast of St. Mary’s, provides an alternate approach to the preferred St Mary's Sound to St Mary's Pool Route location but it requires Crow Bar to be cleared to enter into Saint Mary’s Road. Crow Bar is a shallow sandbank that which dries to 0.7 metres and separates Crow Sound from St. Mary’s Road. The shallowest part of this route is in the Bar Channel and its approaches which only have about 0.5 metres LAT so the course will need a rise of the tide for the vast majority of leisure boats.

The following provides an indication of the depths that can be expected over Crow Bar:

  • • At high water springs, there is 6.4 metres on Crow Bar.

  • • At three-quarters flood, or one-quarter ebb, 5.2 metres.

  • • At half flood or half ebb, 3.3 metres.

  • • At one-quarter flood or three-quarters ebb, 1.5 metres.

  • • At low water 0.6 metres

More cover will be experienced with westerly gales and less with those from the eastward.

Lyonesse Lady passing into Saint Mary's Road past Crow Rock
Image: Michael Harpur

Another visual sign is that if Crow Rock is covered or nearly awash, typically at about 5 hours' flood, the depth in the bar channel will be about 5.5 metres. The state of the tide may also be estimated by the appearance of Crow Rock. It has three distinct heads, called Great Crow, Little Crow, and Crow Foot and they cover as follows:

  • • The Great Crow is nearly awash at 5 hours' flood.

  • • The Little Crow is awash at about 4 hours' flood, or after two hours' ebb.

  • • Crow Foot is nearly awash at one-quarter flood, or three-quarters ebb.

Fortunately, Watermill Cove Click to view haven provides is a good tide wait anchorage on the northwest corn of Saint Mary's. It affords excellent protection from south round through west to northwest, so much so, that anchoring off here would be preferable to continuing the passage into St Mary’s Pool during gales from the southwest and west.

Windmill Cove
Image: Michael Harpur

Although Crow Sound is easy to identify and access it should not be used during any strong easterly or southeasterly winds. The northeast going stream along the southern coast of St. Mary's, turns northward into Crow sound after 0145 Devonport (+ 0500 Dover) and forms a race which extends across the entrance to the sound and out as much as 2 miles eastward from Tolls Island. This lasts for a couple of hours and, in reasonable conditions, should not present a problem, but in a strong wind-against-tide situation, it can be very ugly if not dangerous to leisure craft.

It is essential to also understand that although Crow Sound may be large wide and deep, the area around Crow Bar is not and the waypoints are only as a support eyeball navigation. This part of the passage relies primarily upon a good sounder, clear visibility to support eyeball navigation and moderate conditions. As portions of this area dry at LAT with close-lying rocks to this route, good charts/plotter are vital. Be prepared to take this part of the route under power, in a steady fashion sounding all the way up and through the Bar Channel along the way. Although the principal marks are lit, this is not a passage a newcomer should attempt night nor on the ebb.


Crow Sound from seaward
Image: Michael Harpur

Convergance Point The Coastal Overview for Land's End to Isles of Scilly Route location provides a general seaward overview for approaches to the Isles of Scilly as a whole. Vessels approaching Crow sound from the south-westward should keep a ½ mile from the coast until abreast Gap Point, on the eastern coast of St Mary's, and then steer into the sound. Those approaching from eastward should take care not to open Crow Point northward of Innisidgen. The sound has a wide entrance that is not difficult to identify. Particularly so the northeast side of St Mary's where the Bar Channel is located. This can always be identified by its telegraph and TV tower.

lnnisidgen with the eastern isles in the backdrop
Image: Michael Harpur

From a position east of Saint Mary's, find the traditional alignment of the northeast extremity of Innisidgen, a low and jagged peninsula about 8 metres high which rises to a distinctive conical rocky point, with the summit of Samson Hill, near the southern extremity of Bryher, on 284° T. Pass in on this until ‘Hats’ south cardinal marker, VQ(6)+LF1.10s, is seen then steer for the cardinal mark.

Hats South Cardinal with Great Gannick in the backdrop
Image: James Stringer via CC BY-SA 2.0

This range marker and the cardinal mark lead clear of the dangers through the middle of Crow Sound which are as follows:

  • • Southwest of Trinity Rock, with 4.6 metres and the Ridge 9.7 metres over it, south of the Eastern Isles and Biggal Rock, 1 metre high, located 300 metres south southeast of Great Arthur. Although the former rocks are well covered and deep, they can create breaking seas in bad weather.

  • • Northeast of Vinegar Ledge the north-easternmost danger off Toll's Island off the corner of St Mary’s.

  • • South of Hats shallows drying to 0.6 metres and an uncovering boiler structure from a wreck in the sound. This is marked by the ‘Hats’ south cardinal marker, VQ(6)+LF1.10s, moored 400 metres southward. This is off the traditional Innisidgen transit.

  • • Keep clear of the northeast extremity of Innisidgen as isolated rocks that dry to 1.3 metres extend out 100 metres east-northeast from it. Once the Crow Rock isolated danger beacon is well open of Bar Point these two rocks are cleared.

Innisidgen and Hats south cardinal marker with Biggal rock in the backdrop
Image: Michael Harpur

The course then continues parallel to St Mary's keeping a distance of 150 metres off of the shoreline to Bar Point. Bar Point is a long sandy beach backed by dunes with trees on its raised ground that is stepped back from the point. It is from here that Crow Bar extends northwestward across most of the sound to the north of St Mary's Island.

Bar Point
Image: Oast House Archive via CC BY-SA 2.0

A gap in Crow Bar, called the Bar Channel, lies between the southern end of the drying sand bar and drying foreshore on Bar Point. It is about 150 metres wide and it carries LAT from 0.8 to 1 metre. Unfortunately, almost in the middle of it, there is a rock that dries to 0.2 metres called Queens Ledge that is located about 300 metres northwestward of Bar Point. The Bar Channel waypoint is positioned about 50 metres south of Queen's Ledge rock passing south of the danger and through the channel. Sound careful as nothing can be relied upon in this area of constantly shifting sands.

The next waypoint is located 100 metres north of a second unnamed rock that also dries to 0.2 metres. Located about 300 metres eastward of Crow Rock it is an outlier of the Wras reefs extending from Bants Carn to Bar Point on the northwest corner of St Mary's. There is also the remains of a wreck in its vicinity.

Crow Rock
Image: Michael Harpur

Crow Rock, which may be passed on either side, is then passed on the inside which is the best and more direct route. This route passes 100 metres southeastward of Crow Rock. The rock is steep and marked by isolated danger mark Fl(2)10s.

Crow Rock isolated danger beacon
Image: Michael Harpur

From Crow Bar, the depths begin to increase noticeably as St Mary's Road is entered. The St Mary's Road waypoint is about a ¼ of a mile westward of Creeb Rock. The waypoint has the beacon on a bearing of 050° T (astern), which has been the traditional way to proceed into Saint Mary's Road clear of the Pots and Round Rock.

Creeb with the TV tower in the backdrop
Image: Michael Harpur

This waypoint is also the on the alignment of Nut Rock on a bearing of 260° T in line with the summit of the South Hill on Sampson.
Please note

The latter alignment is useful for vessels intending on proceeding to the Tresco Channel to reach New Grimsby Sound or Green Bay on Bryher. It clears The Pots, that dry to 1.8 metres, and Round Rock, that dries to 1.5 metres, which both lie close together nearly a ½ mile off the southern shore of Tresco.

The 151° transit on the shelter and tower on Buzza Hill
Image: Michael Harpur

The final waypoint sets up the Middle Passage approach to St Mary's Pool with an entry transit that leads in on a course of 151° T between Bacon Ledge and The Cow. The front leading mark of this transit is on a small cream coloured sun shelter, about the size of a bus shelter on the green, with a wide vertical white stripe on a black roof. The rear mark is the conspicuous Buzza Tower, a squat stone tower at an elevation of 37 metres on Buzza Hill, that will be seen on the skyline.

St Mary's Harbour lateral marks with the Scillonian III turning to exit via Crow

Image: Michael Harpur

It is also possible to avoid the ledge by continuing southward to the harbour's lateral marks and pass in this way instead. The port 'Bacon Ledge' buoy, Fl(4)R.5s, is moored 100 metres southwest of the shoal.


The complete course is 3.41 miles from the waypoint 'Crow Sound Range Alignment' to 'Approached to Middle Passage' tending in a westerly direction (reciprocal easterly).

Crow Sound Range Alignment, 49° 55.312' N, 006° 15.312' W
Range finding alignment of the northeast extremity of Innisidgen with the summit of Samson Hill, near the southern extremity of Bryher, on 284° T. This is immediately outside the area where a race could form which extends across the entrance to the sound during bad conditions.

       Next waypoint: 1.47 miles, course 307.05°T (reciprocal 127.05°T)

Hats Cardinal, 49° 56.198' N, 006° 17.136' W
Adjacent Hats south cardinal marker, VQ(6)+LF1.10s

       Next waypoint: 0.57 miles, course 282.92°T (reciprocal 102.92°T)

Bar Channel, 49° 56.326' N, 006° 18.003' W
In the Bar Channel 50 metres south of the Queen's Ledge rock a rock which dries to 0.2 metres and is located about 300 metres northwestward of Bar Point.

       Next waypoint: 0.16 miles, course 264.15°T (reciprocal 84.15°T)

NE Approaches to Crow Rock , 49° 56.310' N, 006° 18.246' W
This is on the alignment of the South Hill of Samson with the beacon on 254° T 300 metres to the northeast Crow Rock. It is positioned 100 metres north of a second unnamed rock that also dries to 0.2 metres and is an outlier of the reefs extending from Bants Carn to Bar Point. There is also the remains of a wreck close south to this position.

       Next waypoint: 0.63 miles, course 236.29°T (reciprocal 56.29°T)

Saint Mary's Road, 49° 55.963' N, 006° 19.054' W
The north end of Saint Mary's Road about 400 metres westward of Creeb and on the alignment of Nut Rock on a bearing of 260° T in line with the summit of the South Hill on Sampson.

       Next waypoint: 0.59 miles, course 185.99°T (reciprocal 5.99°T)

Approached to Middle Passage, 49° 55.380' N, 006° 19.149' W
150 metres outside the Cow Rock and on the entry transit that leads in on a course of 151° T through the Middle Passage into St Mary's Harbour. The front leading mark is a small cream coloured sun shelter, about the size of a bus shelter on the green, with a wide vertical white stripe on a black roof. The rear mark is a conspicuous squat stone Buzza Hill tower at an elevation of 37 metres on the skyline.

What is the best sailing time?
May to September is the traditional UK Sailing season with June-July offering the best weather. The British Isles weather is highly variable, and the amount of bad weather varies quite widely from year to year. This is because they are islands positioned between the Atlantic Ocean and the large landmass of continental Europe. As a result, the entire area lays under an area where five main air masses meet and alternate:

  • • Tropical Maritime Air Mass - from the Atlantic

  • • Polar Maritime Air Mass - from Greenland

  • • Arctic Maritime Air Mass

  • • Polar Continental Air Mass - from central Europe

  • • Tropical Continental Air Mass - from North Africa

Depending on the movements of the jet stream, any and all of these air masses can come in over the isles, creating weather fronts where they meet and bringing with them all types of weather.

The prevailing winds for the British Isles as a whole are from the western quarter which generally blows for two-thirds of the year predominantly from the southwest. Gales from the westward are felt in all seasons, but from November to March, inclusive, they are most frequent and generally last three or four days. Of these, a southwest gale is considered to be the most powerful system. The winter period is largely characterised by wind and rain.

The fine summer weather of the sailing season is typically punctuated by the passage of an Atlantic depression that bringing periods of strong wind and rain, and sometimes poor visibility. These gales rarely cause surprises as they are usually forecasted well in advance. Good weather windows of 48 hours are easy to predict but any longer than that there's an increasing chance of change.

Fogs are frequent in all parts of the Channel and are formed both on the English and French coasts. In summer they only obscure the land in the morning and are readily dispersed by heat or a light breeze. But the moist haze, driven in by westerly winds from the sea, tends to linger and is only dispersed by strong winds. In the eastern part of the Channel, it is rare for the land to be completely free from mists. The only exception is when the wind is from the northeast which makes the mist free coastline highly distinctive from a great distance.

With thanks to:
Michael Harpur, eOceanic.

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