Sailing the Isles of Scilly: Stunning – but challenging – cruising

Falmouth-based David Hackett has cruised in Scilly extensively over many years in his Hallberg-Rassy 37. He gives his guide to sailing the Isles of Scilly

Often referred to as the sunshine isles, the Isles of Scilly enjoy more hours of sun than the rest of the United Kingdom. The archipelago is outstandingly beautiful, uncrowded and unspoilt. Of about 140 islands, only five are inhabited, and the whole area is characterised by turquoise seas and golden white sandy beaches, many accessible only to cruisers.

The Isles of Scilly is also a Conservation Area, an Area of Outstanding Natural Beauty and a Heritage Coast, while having a rich history – 128 listed buildings and 238 scheduled monuments earn it the title of having the highest density per hectare of any English authority. All together, this means the islands really are a cruising gem.

On the other hand, charts of the area show many dangerous rocks with unmarked shallow passages, and hundreds of shipwrecks. In 1707 four Royal Navy warships were shipwrecked on the Western Rocks in severe weather with up to 2,000 sailors losing their lives; this Scilly Naval Disaster led to the Longitude Act and Longitude Prize and ultimately contributed to John Harrison’s invention of the marine chronometer to accurately determine longitude at sea.

Scilly will test your navigational and pilotage abilities when cruising in demanding, yet beautiful, surroundings.

From the mainland

Just as south-east England was originally connected to continental Europe, Scilly was joined to Cornwall. About 12,000 years ago, melting ice caused south-west Britain to start to sink, and coupled with rising sea-levels, Scilly became disconnected from mainland Britain. To begin with it was one single island about 12 miles long, but around 4,000 years ago the single island became five distinct separate islands, some now physically joined only at low tide. The process of reclamation by the sea continues.

The closest mainland ports are Newlyn and Penzance in Cornwall, from which a passage of 36 miles will take several hours and crosses the Land’s End Traffic Separation Scheme. From Falmouth the crossing is 60 miles but with a tidal gate at Lizard Point, whereas from south Wales, southern Ireland or north-west Brittany it is between 120 and 140 miles, an overnight voyage. Sea (advection) fog with poor visibility can be common in spring and early summer when the sea is still relatively cold.

With tricky local pilotage it’s always wise to arrive during daylight. The Isles of Scilly are relatively low-lying and are not visible when far off; only when you are within five miles of the islands will you be able to identify specific landmarks. A pilot is compulsory for all vessels of more than 30m LOA navigating within five miles of the archipelago.

Island pilotage

Passages around and between the islands are tricky, and only the main entrance route for commercial vessels through St Mary’s Sound to St Mary’s Harbour is clearly identified with navigation marks. Entry through Crow Sound should only be undertaken in daylight and requires a sufficient height of tide to cross Crow Bar; charts of this area warn mariners of frequently changing depths due to movement of sand bars.

When arriving at the archipelago, many sailors choose to go to Porthcressa near Hugh Town on St Mary’s, or The Cove on St Agnes, for their first night: both avoid tricky entrances and have straightforward approaches from outside of the islands but are exposed to winds from the south. Other possible first night anchorages include Windmill Cove on the north-east side of St Mary’s, or St Martin’s Bay on the east side of St Martin’s, but they’re exposed to easterly winds.

Care is required when approaching the islands or planning a passage over shallow ground within Scilly: passages between St Mary’s or St Agnes and Bryher, Tresco, St Helens Pool or St Martin’s all dry at low spring tide. Each year, many yachts have unintentionally gone aground when navigating their way across shallow or drying areas.

Plan any such passages on a rising rather than a falling tide, in good weather conditions with a smooth sea and good visibility, and with a reliable and powerful enough engine to stem the tidal flow. The tidal streams generally flow through the islands in a north-east direction during the flood and in a south-west direction during the ebb. However, there are strong tidal streams and eddy currents around the various rocks, islands and channels which can easily push you off your intended course.

Scilly Isles anchorages

The sea bed around the islands is generally sand, shingle or rock; it is not consistently good holding for anchoring. There are no rivers or estuaries, and therefore no mud or clay. There are numerous power, telephone and internet cables running between and around the islands, and every year many are snagged by anchors – use a tripping line! There are several sheltered, firm sandy bays with gentle slopes that dry out and which are suitable for yachts that can take the ground. Green Bay on the east side of Bryher in New Grimsby Sound is always popular for this and is well sheltered from almost all directions. Tresco does not permit yachts to take the ground on any of its beaches except with permission of the Tresco harbour manager.

St Mary’s

St Mary’s Harbour is the main commercial port on the islands and is managed by the Duchy of Cornwall. Many of the moorings are quite close together, and in strong winds yachts may find they lack swinging room. In strong winds from the west to the north, the harbour can be very uncomfortable, and the harbourmaster may advise yachts to leave and find a more sheltered anchorage. There is a dinghy landing pontoon, a toilet and shower block, and a fuel berth all on the main quay. Hugh Town is useful for shopping, restaurants and travel connections to or from Penzance.

New Grimsby

New Grimsby Harbour between Bryher and Tresco is another favourite with cruising sailors. It can be approached at all times from the north through New Grimsby Sound. But approaches from St Mary’s Road between Samson Island and Tresco, or from between Samson and Bryher, and over Tresco Flats are drying and require a sufficient height of tide.

There are 24 visitors moorings and some space for anchoring, though spots with sufficient depth are limited.

The harbour can become rough with strong north-westerly winds and swell; and can be uncomfortable at HW with strong winds from the south or west causing swell. There is good dinghy access to both Bryher and Tresco. Samson Island nearby, once populated but now deserted, is popular with day-trippers in the summer.

Old Grimsby

Old Grimsby Harbour on the east side of Tresco is also popular. It can be approached at all times from Old Grimsby Sound, or with sufficient height of tide from St Mary’s or from St Helen’s Pool. There are five visitors moorings, and space for anchoring for several yachts. There is shelter from most wind directions, except for strong winds from the north-west and south-east; there is nearly always some Atlantic swell rolling into the harbour.

St Helen’s Pool

Anchoring in St Helen’s Pool offers seclusion and good holding in sand or shingle. The roadstead was used by quite large vessels. Although the pool is not landlocked, the islands, rocks and banks around it create shelter in all directions. It is probably the most sheltered anchorage if a strong gale or storm is forecast.

All approaches into St Helen’s Pool require a sufficient height of tide. If you are seeking peace and quiet, there are few other anchorages away from the madding crowd. It is a longer dinghy trip from here to Tresco or to St Martin’s.

Eastern Isles

There are several attractive anchorages among the Eastern Isles, but these should only be used in settled weather conditions; they are not suitable in strong winds or with large swells. There are no facilities in the Eastern Isles.

Where to berth in the Isles of Scilly

There are no marinas, and quays are not available to yachts because of frequent use by commercial vessels, so a dinghy is essential. Visitor moorings in St Mary’s Harbour, New Grimsby Harbour and Old Grimsby Harbour cannot be reserved and get busy in summer months. It would be unwise to leave your boat unattended for any significant length of time; no anchorage is completely safe from storm force winds. Even during summer, storms can develop suddenly; Storm Evert crossed Scilly in July 2021, with gusts of 60 knots (Force 11) recorded. There were 22 emergency calls to HM Coastguard from the Isles of Scilly that night, yachts broke from their moorings or dragged anchors and went aground, with several crews rescued.

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