- \n
- A mast makes the yacht the highest point for miles around on flat water. This significantly increases the risk of a strike.<\/li>\n
- The safest place on board is the centre of the closed cabin, dry and without contact with mast, shrouds, stays and other metal parts.<\/li>\n
- A thunderstorm is dangerous from about ten kilometres away\u2014that's roughly 30 seconds between lightning and thunder. It's only over once no thunder has been heard for half an hour.<\/li>\n
- A lightning protection system reduces the risk for people and hull, but does not reliably protect electronics.<\/li>\n
- After a strike, check hull, through-hull fittings, compass and all electrical equipment, even if the strike is only suspected.<\/li>\n<\/ul>\n
How dangerous is a lightning strike on a sailing yacht?<\/h2>\n
Anyone who stays in a closed cabin is comparatively safe. For the boat's electronics, however, a strike almost always means damage. Most injuries and deaths from lightning on the water occur on small, open boats without a cabin.<\/p>\n
Lightning seeks a path from the masthead into the water. If this path is highly conductive and continuous, most of the current flows along it. If it's missing or interrupted, the current jumps: onto shrouds, engine, rudder shaft, through-hull fittings or people. In extreme cases, such flashovers can blow holes in the hull, especially at through-hull fittings and near the waterline.<\/p>\n
Electronic damage occurs even on boats with lightning protection systems. The overvoltage reaches equipment via the electrical system, aerial cables and the leads from transducers such as echo sounder or log. So after a strike, expect that chartplotter, radio, autopilot and instruments may fail.<\/p>\n
How do you recognise a thunderstorm at sea early?<\/h2>\n
The weather forecast and official warnings give you the earliest notice, shortly before the sky does, and lastly the thunder. Anyone who keeps all three in view gains the time needed for reefing, course changes or making for harbour.<\/p>\n
Weather forecast and warnings<\/h3>\n
In the marine weather forecast from the Deutscher Wetterdienst (DWD), thunderstorms appear in the \"Visibility\/Weather\" line, often with location details such as \"in places\". For the German North Sea and Baltic coasts, the DWD issues coastal warnings around the clock, which also warn of thunderstorms. For some large inland lakes such as Lake Constance, Chiemsee or Steinhuder Meer, there are separate inland lake warnings. How to read the information in the forecast is explained in the article Reading and understanding the sea weather report<\/a>.<\/p>\n
In thundery conditions, pay particular attention to gusts. The forecast gives the mean wind; in a thunderstorm, however, gusts can be significantly higher and strike suddenly. Even on Mediterranean trips, it's worth checking the thunderstorm risk before each passage. An overview of the wind systems there is given in the article The main winds in the Mediterranean region<\/a>.<\/p>\n
What the sky shows<\/h3>\n
Thunderstorms develop in cumulonimbus clouds. You recognise them by high, towering, dense cloud turrets that often spread out at the top like an anvil. The underside is usually very dark, with ragged, low cloud shreds often hanging beneath. Such clouds often produce heavy showers, sometimes hail.<\/p>\n
Important: The first lightning strike can occur before the rain arrives, and even out of a blue sky. Lightning also strikes several kilometres away from the thunderstorm cloud.<\/p>\n
Lightning and thunder: estimating the distance<\/h3>\n
Count the seconds between lightning and thunder and divide by three, and you have roughly the distance in kilometres. Sound travels about one kilometre in three seconds.<\/p>\n
- \n
- Around 30 seconds: The thunderstorm is about ten kilometres away. From here on, it's already considered dangerous.<\/li>\n
- Ten to twenty seconds: The thunderstorm is only three to seven kilometres away; the danger is high.<\/li>\n
- Less than ten seconds: The thunderstorm is dangerously close, around three kilometres or less.<\/li>\n<\/ul>\n
The all-clear is only given once no thunder has been heard for half an hour. Thunderstorms can change direction and return.<\/p>\n
Thunderstorms on a sailing boat: Where does the crew stay?<\/h2>\n
The crew belongs below deck in the middle of the cabin, away from the mast, shrouds, stays and large metal parts. Anyone who must remain outside keeps low, touches no metal and keeps arms and legs inside the boat.<\/p>\n
![\"Sailing](\"https:\/\/www.toernfinder.de\/wp-content\/uploads\/2026\/10\/segelboot-gewitter-hafen-1024x732.jpg\")
Symbolic image<\/p><\/div>\n
Below deck you are considerably safer than on deck. A dry body conducts electricity far less well than a wet one, so it is worth staying as dry as possible. In the cabin, avoid the vicinity of the mast step, chainplates, engine and through-hull fittings, and do not remain directly against the hull at waterline height.<\/p>\n
On deck, the helm position is particularly unfavourable: backstay, boom, rudder stock and engine controls lie close together. If someone must steer, only as few people as necessary remain on deck. Anyone outside crouches low in the cockpit with legs together and touches neither rigging nor guardrails, winches or wheel as far as can be avoided.<\/p>\n
No one enters the water during a thunderstorm. Lightning current spreads through the water over large areas. Even around 100 metres away from a strike you can still receive a painful electric shock in the water. This also applies to swimming in an anchorage and fishing from the stern.<\/p>\n
What happens to the electronics on board?<\/h2>\n
Disconnect the electronics from the ship's electrical system and from the aerials before the storm, as far as possible. You should only transmit during the storm in an emergency.<\/p>\n
Overvoltages reach equipment via cables. A pulled plug or a disconnected cable interrupts this path better than a switch turned off at the switchpanel, because the larger the gap, the better. Retractable or removable aerials that are not part of the lightning protection system should be lowered or removed.<\/p>\n
Plan for the case that the permanently installed navigation fails. A portable VHF handheld radio and a handheld GPS, which are not connected to any ship's cable or external aerial, do not receive overvoltage via the ship's wiring and therefore tend to remain functional. This requires a paper chart and knowledge of roughly where you are. Therefore note down position, course and time in the Logbuch<\/a>.<\/p>\n
In harbour or on open water: What should be done?<\/h2>\n
You are only completely safe in a solid building. In harbour you therefore go ashore; at sea you prepare boat and crew before the storm arrives.<\/p>\n
In harbour and at anchor<\/h3>\n
Boats at the pontoon or on a mooring are also struck. If a thunderstorm is on, you remain in harbour and postpone departure. If one is approaching, you wait out the storm in a building ashore rather than on board or on the pontoon. At anchor the same applies as when under way: below deck, away from metal, no one in the water.<\/p>\n
Under way<\/h3>\n
If the weather forecast announces thunderstorms, you remain in harbour or return earlier. If you are already out, you use the time before the storm:<\/p>\n
- \n
- Reef early or stow sails, because thunderstorms often bring sudden, strong squalls.<\/li>\n
- Put on lifejackets and secure loose items on deck.<\/li>\n
- Position in the logbook, disconnect electronics, have the handheld radio ready.<\/li>\n
- If you cannot reach harbour in time, anchoring can make sense if water depth and distance from shore are suitable. Afterwards the crew goes below deck.<\/li>\n<\/ul>\n
What does a lightning protection system on a yacht achieve?<\/h2>\n
A lightning protection system gives the lightning a fixed path from the masthead to the water and thereby reduces the risk to crew, hull and fire. It does not provide complete protection.<\/p>\n
The system consists of three parts: an air terminal at the masthead, a down conductor and earthing in the water. With an aluminium mast, the mast itself serves as the down conductor. The earthing is provided by an earthing plate beneath the hull or a lead keel connected via the keel bolts. Fresh water conducts considerably less well than salt water; on inland waters the earthing therefore needs substantially more area so that the current does not jump into the water via through-hull fittings or the hull.<\/p>\n
Below the air terminal an approximately cone-shaped zone of protection is created, in which the risk of a direct strike is significantly lower, but not zero. For planning and installation there is an international technical standard<\/a> for boats up to 24 metres hull length (as at: October 2026). It too does not promise complete protection against injury and equipment damage. When the boat is ashore the system does not protect, because the earthing in the water is missing.<\/p>\n
Against electronics damage, surge protection devices fitted directly to each piece of equipment can additionally help.<\/p>\n
What do you check after a lightning strike?<\/h2>\n
First the integrity of the hull, then compass, electrics and rigging. Check even if you only suspect that lightning has struck.<\/p>\n
- \n
- Inspect bilge and hull: Has water entered? Look at through-hull fittings, seacocks, transducers and the hull near the waterline for cracks and holes.<\/li>\n
- Compare the compass on several courses with the GPS course, taking variation and current into account. A lightning strike can alter the magnetic properties on board; the compass deviation may no longer be correct afterwards.<\/li>\n
- Test all devices individually: radio, plotter, autopilot, instruments, navigation lights, bilge pump and engine electrics.<\/li>\n
- Inspect the rig: masthead, aerial, wind sensor, shrouds and chainplates for signs of scorching and discolouration.<\/li>\n
- Look out for the smell of burning and warm cables.<\/li>\n<\/ol>\n
Minor damage to the underwater hull is often not visible from inside. Only an external inspection will give certainty, either on land or by a diver. Photograph all damage and record the time and position in the logbook.<\/p>\n
Practise seamanship underway<\/h2>\n
Learning to read the weather, reef in time and organise the crew in strong winds and thunderstorms is best done on longer passages with experienced skippers. On T\u00f6rnfinder you will find Mile building<\/a>on which you sail for several days and nights at a stretch, and sail training<\/a>on which seamanship is specifically practised.<\/p>\n
Frequently asked questions<\/h2>\n
Is one safe in the cabin of a sailing boat during a thunderstorm?<\/h3>\n
Largely, as long as you stay in the middle, remain dry and do not touch the mast, shrouds, engine or other metal parts. You are only completely safe inside a solid building ashore.<\/p>\n
At what distance is a thunderstorm dangerous?<\/h3>\n
Typically from about ten kilometres onwards. If less than ten seconds pass between lightning and thunder, the storm is only about three kilometres away.<\/p>\n
Should one switch off the electronics on board during a thunderstorm?<\/h3>\n
Better to disconnect than just switch off: pull out plugs, disconnect aerial cables wherever possible. Use the radio only in an emergency. A handheld VHF and a handheld GPS with no connection to the ship's system serve as backup.<\/p>\n
Does the compass need to be checked again after a lightning strike?<\/h3>\n
Yes. Compare the compass on several courses with the GPS course. If it deviates, have it recompensated before relying on it again.<\/p>","protected":false},"excerpt":{"rendered":"
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