The Sea State - Part 4 Planning a Coastal SUP Journey

The Sea State - wind, tide and swell

Understanding how a set of forecasts will translate into the sea state and so affect you on your journey is the real key.  There are prevailing conditions which mean that certain locations would be considered too challenging in most conditions.  The North Coast of Cornwall is likely out of bounds 95% of the time, due to the Atlantic swell. 

The sea is different every moment of every day, it is affected by the wind, tides and swell,  individually and as complex combinations.  Coastal features big and small make a big difference and not forgetting banks and rock formations that lie underwater.

There is usually a link between how dramatic and high the coastline is, and how challenging a SUP is likely to be.  The East Coast of the Lizard at Porthallow, where there are lots of small coves and small cliffs around 20 m high, verses the West Coast at Kyanance Cove where there are few beaches and imposing cliffs around 70 m, illustrates the difference well. 

This is a quick guide but be mindful that people spend a lifetime building up knowledge of the ocean and weather.




I find that novice paddlers can paddle comfortably in up to 12 mph winds.  They make good progress with rests up to 14 mph (more if kneeling), and a short concerted effort can be made up to 18 mph.  This is extremely subjective dependant on so many factors.  The lower the winds, the lower the risks.  This means that there are many more choices of locations in light wind conditions.

Wind can help or slow your progress at sea as it would on a lake.  A one way journey is often attractive as you can achieve greater distances, using the wind to your advantage. 

Wind chop is tricky to deal with, it is unpredictable and difficult to balance on.  The all purpose entry level Paddle boards are unable to cut through it, often stalling when they hit a bump.  This affects the speed of the board, the energy you use, causes falling in, moves you down from standing and so may affect the viability of the paddle (it’s good fun and great for balance for short periods).

The Beau Fort scale offers a guide this link shows pictures from a large ship, but on a SUP you are up close and personal.  I find in upper Force 4 novice paddlers need good of shelter.

The wind creates more chop the larger the expanse of water and so a moderate offshore wind correlates with a flat sea state close to shore.  Being blown off is a consideration. 

There are some great forecasting websites, some specialising in recreational boating.  In summer and in Cornwall they are very reliable at 3 days and good at 5.  The sites do not always get it right and when they disagree or change the forecast significantly, the alarm bells ring.

Be specific on your location, in Cornwall you can have sunshine on the North coast and at the same time flooding in Falmouth on the south coast.  Here are my favourite forecasting sites, they do use different forecasting models and I always check more than one especially when the forecast is borderline for my planned actvity:-


Wind guru –

XC Weather -


Met Office -



Swell is produced many miles away by wind.  www.MagicSeaweed.Com is a firm favourite for its detailed predictions.  Swell is described by its direction, height and interval, the longer the interval (time between the swells) generally the more powerful the wave and the better for surfing. 

It is important to consider swell when planning a journey.  A 3 foot swell with a big interval may be relatively easy to paddle on in the open sea, it can be rhythmic and predictable, gently causing you to rise and fall.  However when you wish to land, it will be extremely tricky.  On route the swell will react with any rocks or features, creating breaks where you did not necessarily expect them. 

I take novice paddlers out in up to 1 foot swell and experienced flat water paddlers in up to 2 feet.

Swell has many components, and Magic Seaweed predicts secondary swells.  I study these closely as they may cause you to switch coasts or even put you on the River.   An unusual easterly swell rules out some of my favourite and usually sheltered paddles in Cornwall.



The ebb and flow of the tides has been reliably predicted for centuries.  The Gravity of the moon pulls the oceans around twice a day.  Each day the tide gets an hour (ish) later and the exact time of day of high and low tides varies depending on where you are. is easy to use and provides a lot of detail on tides.  Search for the specific launch site (or largest port) for more accuracy. 

There are spring and neap tides depending on the moon’s orbit.  On neap tides the high is around midday and there is little height change meaning that the volume of change in water is not great and so the tidal flow is relatively small.

On a spring tide the low is around midday and the change in height of water is great, making the tidal flow much more significant.  There is a variation even in spring tides, where just a few times a year there are ‘big’ spring tides, these are often associated with coastal flooding and terminology like a ‘Super Moon.’

The tides and the changing height are not linear through the cycle.  ‘The rule of twelfths’ defines the rate of change in height, it is used a lot in sailing navigation.  You will have observed it on the beach, where at low and high tide there is slack water (little movement of water) and mid tide (low +3 hours) the tide races in (particularly on a spring tide). 

‘My Grandma’s favourite past time was to sit on a rock with a cuppa and watch sunbathing tourists encamped in the middle of Chapel Porth beach surrounded by their things  as the water enters the cove picking up speed and threatening to douse them.’

On a tidal estuary the tides are key, as at low tide there may be sand banks or worse mud banks, making areas inaccessible.  There may be narrowing of the river with large expanses of water requiring high volumes up river.  This funnelling creates fast moving tides that can be difficult to paddle against (great to paddle with).  The Gannel, Crantock is a great example of this with a salt water lake upstream of a narrow channel.

On the coast the level of tidal flow is less noticeable except if there are coastal features such as headlands, more about this later.

I find that paddling in a big spring low tide is amazing, exposing rocky outcrops and much sea life not usually visible.  At any low tide there is likely to be more shelter behind rocky outcrops.  At high tide any swell can break right against the cliffs without being broken down.

At sea, the state of the tide affects access, there may be a long walk to the water on a spring tide.  More importantly its relationship with the wind and the features of the coastline should be considered.

Wind against Tide

As the title alludes, wind against tide occurs when they are coming from opposing directions creating a disturbance in the sea state.  A flat calm stretch can turn almost instantly into a maelstrom of lumps and bumps as the tidal flow increases.  Carrick Roads is notorious for this as creeks and rivers merge and the water opens out.

Part 1: Introduction

Part 2: Setting Goals

Part 3: Research & Plan

Part 4: The Sea State - wind, tide and swell

Part 5: Coastal Features

Part 6: The Journey Plan

Part 7: Equipment & what to wear

Part 8: In an Emergency

Part 9: The week of the paddle

Part 10: The Adventure Begins