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Island Life - Josh Sedgeman and The Tides

28 February 2018

Josh Sedgeman - The Tides

The tide can be a very confusing concept for people who don't live by the coast, but as an islander and a boatman, your life tends to revolve around it. Find out more about the tide and how it works and changes from Josh, boatman and island resident.

What is the simplest way to explain the tides?

Well in very simple terms the tides are caused by the gravitational pull of the moon and the sun. As we circle the sun and the moon circles us, they pull the water towards them which in turn creates a movement of water, otherwise known as tides.

How far ahead of times can the tides be told?

Basically, as long as the moon cycle remains as it is now then as far as you could imagine. One thing that is changing is rising sea levels so the further into the future we predict, the less accurate it will be.

On average, how long is the causeway covered for, and how often in a 24-hour window?

Well it’s roughly 4 hours in every 12 the tide is open so it is covered around 16 hours over a 24 hour period

Why do the tides change each day?

The Tides get later by around 45 minutes every 24 hours. This is because the moon cycle, a lunar day is around 24 hours and 45 minutes, slightly longer than our day. 

Why are the tide times different at different points along the coast?

Another key factor how tides work is the rotation of the earth. As the earth rotates, the sun and moon’s strongest gravitational pull starts to work it’s way to another spot. 

What is a spring tide?

A spring tide is when the tide moves faster and is a bigger tide.They occur when we are on a full moon or a new moon. Spring tides are caused when the sun, earth and moon are in line. You can always tell when we have a spring tide on the island, if you can walk through the harbour gaps with dry feet at lunchtime, we are on spring tides.

What is a neap tide?

A neap tide is when the tide moves a lot slower and the height of the tide is smaller. Neap tides are caused when the moon is a half moon and is at 90 degrees to us and the sun. For us, on the island, these tides are harder to predict the opening and closing times of the causeway. In general, the weather is usually slightly worse and with tide moving slowly, the margin for error gets bigger. However as boatman we very much enjoy neap tides, we get to spend the whole 8 hour day on our boats as high tide is around lunchtime. 

How often do these types of tide occur?

We get 2 spring tides and 2 neap tides every 28 days, which is a complete lap of the moon cycle

What is groundswell?

When you see big breaking waves on the beach, this is groundswell. It is caused by a combination of a drop in atmospheric pressure and strong winds that come from out at sea. For us as boatmen, any strong winds coming from anywhere in the south usually means we will get a form of groundswell. This is because the only land shelter for a few 100 miles is the island itself. We have a lot of days where the wind can be strong and you see lots of ‘white horses’ in the bay, but this is just surface chop. Even tho we are getting wet and it can look worse, the size of the waves are smaller. 


What are the different landings the boat go to, and at what tidal point do you know when to go to them?

We have 4 landing points that we use as Boatman for St Michaels Mount. One is fairly obvious, the island itself. On the mainland, we have 3 landing points; Chapel Rock, Gwelva and Top Tieb. As the tide comes in and the causeway covers, we have a channel dug in the beach to Chapel Rock which is our first landing. Once the bottom step on ‘kings steps’ in the mount harbour is covered, we know we have enough water to get a boat into Gwelva and we don’t have a lot of time left before Chapel Rock also becomes an island. We try to stick to these 2 landings but when we are on spring tides or the weather isn’t great we also have a small harbour, Top Tieb.