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Gascanane Sound Cut - 'Eastern Pass'

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What is the route?
This is the 'eastern passage' of the two passages available through Gascanane Sound in southwest County Cork. These provide vessels with a short cut between Sherkin Island and Cape Clear Island that avoids the longer route around Cape Clear Island. The sequence of description is from south to north but it may be used either way with the benefit of a fair tide.

Why sail this route?
This is particularly convenient route when moving from Baltimore to Cape Clear North Harbour (Trakieran) where the cut saves at least an hour’s sailing. It may also be used by vessels going further north into Long Island Bay, sailing to destinations such as Schull Harbour for instance, or even Crookhaven where it will still save at least half an hour.

The 'eastern passage' is the preferred of the two cuts as it is deep, has its dangers always visible on both sides and is the wider of the two passes. The 'western passage' Route location is however a slightly more direct a cut to make for vessels bound for North Harbour (Trakieran) on Cape Clear Island. In all cases, the southern approach waypoint provides is the same for both passes. So the best pass to take in existing conditions can be taken at that point.

Tidal overview
Today's summary tidal overview for this route as of Friday, April 19th at 07:46. The east going tide starts running southeastward at -0030 Dover (+0520 Cobh). The west going tide starts running northwestward at +0540 Dover (–0055 Cobh).

Northwestward Stream

(HW Dover +0540 to -0030)

Starts in 07:39:47

(Fri 15:26 to 21:41)

Southeastward Stream

(HW Dover -0030 to +0540)

Starts in 01:29:47

(Fri 09:16 to 15:26)

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.


The challenging Gascanane Sound is a channel that separates the southwest end of Sherkin Island from Cape Clear Island. It lies between Cooslahan Point, the eastern extremity of Cape Clear Island, and Illaunbrock, an islet off the southwest extremity of Sherkin Island. The Sound is about a mile wide and is divided into two channels by the Carrigmore and Gascanane Rocks.

The former Carrigmore Rocks are located about 800 metres northeast of Cooslahan Point and are a group of high rocks that dry to 6.1 metres and never cover. The latter, Gascanane Rock, lays nearly 180 metres west of the Carrigmore Group and dries to 1.8 metres but cover at half-flood.

Two yachts passing in the 'western passage' between Carrigmore and Crab Rock
Photo: Becky Williamson

The tides sweep through both channels, especially at Springs, with such velocity as to cause dangerous eddies and it should only be approached with a commanding breeze, a reliable back up engine plus good visibility and favourable tides. Expect broken water in brisk conditions.

The advantage of taking the cut is it avoids passing around the imposing three miles long, south-westward lying, Cape Clear Island. But if there is any doubt, head around the island. If the tide is unfavourable in Gascanane Sound the Baltimore Harbour north entrance Route location route could provide a better cut, especially so for vessels already moored in Baltimore Harbour.


The complete course is 0.82 miles from the waypoint 'East & West Channels Southern Approach' to 'East Channel Northern Approach' tending in a northerly direction (reciprocal southerly).

East & West Channels Southern Approach, 51° 26.800' N, 009° 27.070' W
This is about ½ a mile southward of the Carrigmore Rocks.

       Next waypoint: 0.46 miles, course 12.50°T (reciprocal 192.50°T)

East Channel Midpoint, 51° 27.250' N, 009° 26.910' W
Midpoint eastern passage

       Next waypoint: 0.36 miles, course 347.94°T (reciprocal 167.94°T)

East Channel Northern Approach, 51° 27.600' N, 009° 27.030' W
This is about a ⅓ of a mile northeastward of the Carrigmore Rocks.


This passage is between Carrigmore reef and Illaunbrock and is the preferred of the two cuts as it is deep, has its rocks visible on both sides and, being almost a ⅓ of a mile wide, is the more generous of the two passes. Likewise, Illaunbrock, though foul to the north, is fairly steep on its southern and westerner sides.

Care is still needed with the currents whilst passing through the cut. When taking the eastern passage the vessel will be steering roughly north or south whilst the tidal flow is slightly crosswise running roughly northwest and southeast. Therefore a vessel passing northward will have the current setting onto the Carrigmore Rocks, awash, or when going southward on to Illaunbrock.

The key to using either of these cuts is to work the tide. The streams set strongly through the sound attaining a rate of 3kn during Springs causing eddies. The east-going stream set southeastward, and the west going stream sets northwestward. They begin at the following times:

  • • The west going tide starts running northwestward at +0540 Dover, or at –0055 Cobh

  • • The east-going tide starts running southeastward at -0030 Dover, or at +0520 Cobh.

Cross tides tend to can set a vessel onto the rocks in the eastern channel.

The waypoints are for guidance only as this cut centres on pilotage and should only be used in moderate conditions with good visibility. There is nearly always a groundswell entering the sound which can make the passage look threatening.
Please note

Vessels bound to or from North Harbour or Crookhaven, should keep well offshore north of the Cape Clear Island to avoid Bullig Reef. Bullig Reef extends out a ¼ of a mile northwest from Illauneana, an islet that lies 300 metres north of Cape Clear Island. It is very much in the way of a passage west from Gascanane Sound.

What is the best sailing time?
Sailing season is May to September, with June and July offering some of the best weather. Nevertheless, the incidence of gales in June and July are on average two days of winds each month of winds up to force seven. So you may be either held up or having a blast depending on your sailing preferences. Ireland is not subject to persistent fog statistically complete days of persistent fog occur less than once in a decade.

Are there any security concerns?
Never an issue known to have occurred sailing off the Irish coast.

With thanks to:
eOceanic & Burke Corbett.

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