You have crossed the Atlantic Ocean in a ship to Ireland. You are tired and hungry and desperate to deliver your expensive cargo to port.
You sail the coast from the Fastnet Rock and, from a vantage point of a few nautical miles, all you can see with your telescope is a continuous line of coast and not the harbour you seek.
Any navigational aid is a potential lifesaver.
Our coast has hundreds, if not thousands of navigational and military markers to aid mariners through our rough seas.
There are markers of all sizes, shapes and sophistication to indicate dangerous rocks, reefs and cliffs.
There are signal towers around the coast which were constructed to warn the British of a possible French invasion in the 1810s.
Privately built navigational aids were also constructed to assist domestic and international trade.
One such occurs at Horse Island, Co Cork, at the mouth of Castlehaven Harbour.
In the 18th century, ships owned by Tom Somerville of Drishane House, plied their way from Castlehaven to Savannah, Georgia, in America.
Any mis-tracing of the route was hazardous, potentially fatal. You only have to look at the database of wrecks off the south coast to see the continuous record of disaster that has befallen such ships.
Without accurate guidance, some of Somerville’s ships entered the wrong harbours — such as Glandore’s — and endangered the lives of the crew, the ship, and the cargo, and potentially dealing a fatal blow to the business.
To deal with the problem, Tom constructed a sturdy round limestone tower of about 5m in height which was easily sightable by approaching ships and was the signal for home.
The tower has a door but no roof and was never designed as a dwelling. It was built around 1770.
The great, great, great, great, great, grandson of the merchant, also Tom Somerville, now lives in the family estate Drishane House with his family. He takes up the story.
“Tom had intended becoming a minister in the church like his father but he lost an eye at Trinity and the story handed down was that, as man is made in the image of God, he, with only one eye, couldn’t enter the ministry. He set up a merchant shipping business instead,” says Tom.
“He had a fleet of ships and they traded with America and they kept missing the turn in to Castlehaven/Castletownshend so he built the tower to ensure they didn’t miss it any more. When you’re out at sea it’s very difficult to distinguish.
“The main trading base was Savannah, Georgia. That’s where his three brothers were.
"He wasn’t limited to Savannah and they also traded with the West Indies.”
The ships from America unloaded their cargo on the Castletownshend quays which Tom built opposite the castle.
Goods were also stored in warehouses at the quay. Then the goods were distributed by wagon around West Cork to the purchaser.
The modern descendent says: “If you lost a ship you lost a huge part of your capital and of course the men crewing it. Tom also sailed to America himself on some occasions. The brothers went to America to seek their fortune just before the revolution .”
Trading declined after the revolution as everything was in a state of flux. A lot of the family money was lost as a result.
Tom died in 1792 and his son got out of the business.
Horse Island stayed in the ownership of the Somerville’s until the 19th century when Tom’s great, great uncle sold it for £100.
In the 1970s, the island was used to graze sheep by the Sokolov Grant family of White Russian lineage who lived at Castlehaven House, once the vicarage of the church.
Sheila Sokolov Grant was a journalist and a former friend of the German Adam Von Trott, who was part of the Hitler assassination attempt.
There are at least nine Horse Islands in Ireland. The island has a graveyard which is marked on the Ordnance Survey maps.
According to local tradition one of the McCarthy-Townshends is buried there.
How to get there: Ask at Castletownshend pier.
Other: drishane.com; archaeology.ie/underwater-archaeology/wreck-viewer; Parting of the Ways, Shiela Sokolov Grant