This is a passage across the broad stretch of shallow water that lies to the east of Tresco to allow vessels in Old Grimsby Sound to connect to St Mary’s Road. Large sections of the route are shallow and parts dry to 0.4 metres LAT so a sufficient rise of tide is required and it is ideally addressed on the flood. The route is sequenced from to St Mary’s Road to Old Grimsby Sound but it may is available both ways.

Image: Tom Corser 2009 via CC BY-SA 2.0
Why sail this route?
Using this internal cut saves hours of sailing for those planning to pass around the north side of the island group in order to address Old Grimsby
Image: Michael Harpur
This route can be used in conjunction with Crow Sound to Tean Sound
- • Breaking off eastward for ½ a mile, between the Pentle and Lizard Point waypoints to the 'Central' waypoint of Crow Sound to Tean Sound
provides access to the routes destination of Tean Sound
.
- • The 'Central' waypoint is on the Men-a-vaur alignment which safely leads northwestward to St Helen's Pool
(St Helen's Island).
- • Likewise, to the southeast, the same alignment has the initial fix for Higher Town Bay
(St Martin's).
- • And finally close south of the 'Hats' commencement waypoint is the Watermill Cove
(St Mary's) anchorage.
In a group where no anchorage provides complete protection, all of the time, and vessels have to prepared to shift in order to make the best of the weather, this ability to quickly cut between all of these anchorages is more than useful. Likewise, with a least depth of about 0.5 metres, this should not prove over limiting and particularly so during Neaps when, with a tidal range of 2.3 – 5 metres, it is a reasonably available option for most vessels most of the time. Using this internal cut saves hours of sailing for those planning to pass around the north side of St Martin's. In suitable conditions, it can also provide an enjoyable piece of pilotage.
Tidal overview
Today's summary tidal overview for this route as of Friday, February 26th at 21:47. With large a small section of this route drying to 0.4 metres, a rise of tide will be required for vessels carrying any draft. Vessels carrying up to 1.3 metres can as a general rule proceed 1 hour after LW and freely pass during Neaps. Vessels of 1.8 metres should wait for 2 hrs after LW, which the timer set for 4 hours before and, conservatively, 2 after. For more detailed work:MHWS 5.7m MHWN 4.3m MLWN 2.0m MLWS 0.7m
Highest Astronomical Tide (HAT) 6.4m, Mean Sea Level (MSL) 2.91m
Shallow (HW +2 to -4 Hours)
(HW ST. MARY'S +0200 to -0400)
Now
(Tidal flow )
Ends in 03:02:06
(Fri 18:25 to 00:50)
Tidal Window (HW -4 to +2 Hours)
(HW ST. MARY'S -0400 to +0200) 
Starts in 03:02:06
(Sat 00:50 to 06:50)
What are the navigational notes?
Crow Rock North, 49° 56.455' N, 006° 18.602' W
400 metres north by northwest of the Crow Rock isolated danger mark Fl(2)10s and on the 160°T transit of the danger mark and the TV tower on St Mary's.
► Next waypoint: 0.15 miles, course ⇓ 348.13°T (reciprocal ⇑ 168.13°T)
Cones, 49° 56.602' N, 006° 18.650' W
40 metres east of the cones ledge, a small outlier of the Diamond Ledge, drying to 5.4 metres, off of the southeastern extremity of Tresco.
► Next waypoint: 0.31 miles, course ⇓ 336.82°T (reciprocal ⇑ 156.82°T)
Little Pentle, 49° 56.883' N, 006° 18.837' W
On the 160°T transit of the danger mark and the TV tower on St Mary's and 160 metres east of Little Pentle.
► Next waypoint: 0.33 miles, course ⇓ 341.31°T (reciprocal ⇑ 161.31°T)
Lizard Point, 49° 57.195' N, 006° 19.001' W
200 metres east of Lizard Point.
► Next waypoint: 0.42 miles, course ⇓ 329.07°T (reciprocal ⇑ 149.07°T)