Donate now
A lighthouse in rough seas

Seven things RNLI crews can teach you about weather and tides

St Mary's Severn class lifeboat off Bishop Rock off the coast of the Isles of Scilly Photo: Photo: RNLI/Nigel Millard

Understanding weather conditions is a key part of RNLI training. How can you use what our volunteers learn to stay safe on the water? 

The days when lifeboats were solely crewed by local fishermen and sailors are long gone. Today, over 95% of lifeboat volunteers have no seafaring background when they join. 

But whether you’re crew on an all-weather Severn class lifeboat or just enjoying an outing on a little dinghy, an understanding of weather and tides is essential to ensure you enjoy the best – and safest – experience on the water. 

Here we take a look at seven things RNLI crews are taught about weather and tides. 

Two crew members on deck in heavy sea spray and rain

Photo: RNLI/Nigel Millard

1. How high are the tides? 

‘Knowing the tide times is important if you want to be able to safely navigate on the water,’ says RNLI Lifeboat Trainer Adrian Bannister. ‘You need to continuously monitor depth and maintain adequate clearance between the lower part of your boat (its draught) and the sea bed when afloat. For our crews, tide height can affect everything from the way they conduct search operations, to the speed with which they can reach a casualty’s location.’ 

There’s an array of places to get information from. Almanacs, apps, and local timetables all have information pertaining to specific areas so you can work out the times of high and low tide. Many options rely on information from the UK and Ireland hydrographic offices. You can get the information direct at Admiralty EasyTide. You can also source tide height and stream information from some electronic chart plotters. Don't be surprised if the figures are different on different models - just like getting a different weather forecast on different apps!

Make sure you know where your echo sounder is calibrated to measure from. A lot of water users adjust it to display the depth of water from the lowest part of their boat. The helm must know the minimum depth they’d expect to see, and that the standing order is to stop the boat if the depth drops beneath that. A top tip is to set a depth alarm to alert you if you enter shallow waters.

2. Springs or neaps? 

As well as the heights of tides, it’s useful to know about ‘springs’ and ‘neaps’. Spring tides are not related to the season. They’re caused when the moon and the sun align during a new or full moon. The height difference between high and low water is much larger during spring tides. This also means more water moves, flowing faster. 

Spring and neap tides rotate within a 28-day cycle, with 7 days between them. Neap tides have a smaller tidal range, meaning the height doesn’t fluctuate as dramatically.

An RNLI lifeboat conducts a search in rough seas

Photo: RNLI/Paul Appleton

Newhaven lifeboat conducts a search in rough seas

If in doubt, take a look at the phase of moon and you’ll be able to work out whether you’re closer to a spring tide or a neap tide. 

‘For lifeboat crews, knowing when it’s a spring tide can make a big difference to a rescue,’ says Adrian. ‘The higher high tide could see the lifeboat get to places that it normally couldn’t reach on the water. Conversely, at low tide, it may be unable to get somewhere that it could normally reach. Knowing the difference is vital to planning out a successful rescue. For you, knowing the tidal height could help you navigate through areas of shallow water, or get you in and out of harbour safely.’ 

3. Confused seas 

A key term that lifeboat crews are taught about is ‘confused seas’. Confused seas are defined by irregular wave patterns, and can be found at harbour entrances and near headlands. They're particularly difficult to navigate because they cause such unpredictable motion.

If you’re in an area with potential for confused seas, ensure both you and your passengers are extra vigilant on deck. 

4. Tidal stream 

Another thing that crew members have to be aware of is the tidal stream – how fast and in what direction the water is flowing. To do this, they use either a tidal stream atlas or tidal diamonds. The atlas works by displaying arrows on a map. These arrows vary in length and thickness, the size indicating the strength of the current. It will also show the speed of the current during spring and neap tides, measured in knots. 

‘You may have seen tidal diamonds on your nautical charts. The numbers in these diamonds correspond to a chart, and you can crosscheck between the two to find the current in that area,’ Adrian explains. ‘Knowing the speed of the current can be vital to a successful search operation. Crews will also sometimes look for visual clues, such as the speed and direction of seaweed or bubbles in the water.’

5. Bring the weather (forecast) with you 

With up-to-date marine-weather forecasts available online and on apps, there’s no good reason not to check the forecast before you go out and during your journey. You’ll need to know the wind speed and direction, the sea state, what the weather conditions and visibility are like. You also need to know if the weather that’s been forecast is ‘imminent’ (expected within 6 hours), ‘soon’ (between 6–12 hours), or ‘later’ (more than 12 hours). 

Two RNLI lifeboat crew members stand on deck during rough conditions

Photo: RNLI/Nigel Millard

Sea state has a big effect on search operations

Whether you use the Met Office and Met Éireann or other sites and apps, make sure you not only check the forecast for the day and future (in case it comes through earlier than anticipated), but also weather in the days leading up to your passage, as it may have created sea swell. 

And remember you may lose phone signal on the water, so take printed tide tables, charts and forecasts as a backup. Also keep a listening watch of VHF Channel 16, where the coastguard issues MSI broadcasts – including inshore waters forecast – every 3 hours. 

‘Lifeboat crews pay particular attention to the wind fetch – the distance wind travels unobstructed over water,’ Adrian says. ‘If the wind travels long distances, it creates larger waves, making areas more difficult to navigate. Crews check the wind direction and plot their route accordingly. Try to avoid areas where the wind is also blowing against the direction of the tide, as this will create more confused wave patterns, and potentially a choppier, more violent sea state. In this case, sailing in deeper water, where the waves are calmer, may be easier.' 

6. Weather card 

All crew members have a weather check card on their person. This card describes the Beaufort Wind Scale and what the different levels mean. So if they hear ‘Force 7’ on the radio, they know it’s a near gale with speeds 28–33 knots. The card also has information on the sea state, which breaks down what each state means, as well as visibility. 

‘It’s important for crews to give an accurate description of the conditions they’re facing,’ says Adrian. 'This will be relayed to the coastguard who then use it to adjust certain factors, especially on a search operation.’ 

It might be a good idea for you to create your own weather ‘cheat sheet’ that breaks down terminology into easily understandable terms. That way, if you listen to a forecast on the radio or need to provide information over your VHF, you can be as accurate as a lifeboat crew member.

A lifeboat crew member checking his charts

Photo: RNLI/Nigel Millard

Check your charts for depth and current information

7. Preparation is key 

All the classroom exercises and training routines are designed to help RNLI crew members react rapidly and confidently to sea conditions. Practice and preparation are key to a successful rescue. And that’s something you can do too. By checking the weather and tides in advance, and using the knowledge that RNLI lifesavers are given, you can enjoy the water more safely – whatever the weather.

Safety tips 

Adrian Bannister, RNLI Lifeboat Trainer, shares his top tips:

'When it comes to planning a passage, you should use APEM – appraisal, planning, execution and monitoring. Appraising and planning means getting the information before you depart. Monitoring means keeping an eye on the depth sounder and listening to weather forecasts on the VHF. 

It’s also about knowing when to set sail and when to wait. For example, a harbour entrance might be inaccessible when it’s wind against tide, but you know the direction of tide will change in a few hours – meaning the wind will be with the tide, making it safer to enter.'

Looking for more sailing advice? We've got you covered.

Get sailing safety tips

Originally published in Offshore Summer 2022