Lightning strikes the masthead and loads the entire rigging, the boat must have a conductive path to channel the load to the water. Otherwise, between the lower parts of the rigging, e. If, on its way to connect to the sea, the electric arc encounters such poor conductors as fiberglass, wooden bulkheads, or a teak deck, the heat above the surface of the sun will literally atomize the obstacles.
In case of direct lightning strike from a boat poorly connected to the ground, the colossal energy can deform the mast, damage the shrouds, a teak deck can catch fire or explode by vaporization of water, the composite can locally turn into plasma.
These are the extreme risks, generally we will deplore less important damages often limited to the electronics on board, either that we were lucky that the lightning struck a little bit nearby or that the grounding worked well. Lightning damage affects all electrical equipment, especially but not only those with wired connections.
With an extremely intense electric field such as that of lightning, if grounding allows most of the energy to be diverted to the sea, the induced electric fields will be destructive to electronics. We see the VHF antenna, the anemometer, the masthead light disappearing. On board, the electrical panel smokes, the fuses have burned out, the autopilot is often out of order, the battery charger and the controller are out of order, as are the car radio and the GPS, but also the starter relay, the alternator, the solar panel regulators, etc.
The first reflex is to disconnect the batteries, as their deterioration would make further navigation very complicated. The illustrations in Figure 6 show what happens on board a bonded bottom and unbonded top boat during a lightning strike. On the unbonded boat large voltages develop between the mast, chainplates, forestay, backstay, wheel, rudder post, toe rails, electronics, wiring, metal reinforcing in plumbing fixtures, engine, etc.
These make working the boat extremely hazardous, even if lightning is not striking the boat directly. On the bonded boat these voltages are shorted out by bonding conductors. Note, however, that the large magnetic fields associated with a direct lightning strike make the concept of an electrical "short" a misnomer.
Appreciable voltages can develop between the ends of long conductors even if the conductors are connected together at their other end. The helm is a particularly dangerous place owing to its proximity to the engine controls, boom, rudder post and backstay. The helmsman in Figure 6 bottom would not be smiling if he had one hand on the tiller and the other on the engine controls, for example. Note that he is steering with one hand in his pocket to minimize the risk of making a connection between two conductors at different voltages.
This is not as safe as throwing over the anchor and going below! For stations such as the helm that are usually manned, it is crucial that the bonding conductors should be kept as short and straight as possible. Electronics Electronics-killing overvoltages may be introduced through the DC power wires, antenna input, or any other external connection such as a lead to a transducer.
Electronics on a small sailboat that are struck by lightning are particularly difficult to protect since it is impossible to divert the lightning current any appreciable distance away from" the electronics. This difficulty, and the pervasive nature of electronics damage, is illustrated in Figure 7 that shows the percentages of boats with electronics damage of different magnitudes.
In this case there is less of a distinction between boats struck in fresh water versus salt water as there was for hull damage, but the same trend is evident: boats with protection systems in salt water fare best and boats with no protection systems in fresh water fare worst. Apparently a lightning protection system, as installed on the boats in the survey, does not necessarily save the electronics.
Note that for these boats "lightning protection" merely meant that the boat was grounded, not necessarily bonded with transient protection devices, as explained below. In order to protect electronics, more is needed than merely diverting the current to ground water without its blowing a hole in the hull. Due to the low voltages typically used in modern marine electronics, just a few extra volts is enough to cause extensive damage.
However, techniques that are used to protect computers, cable TV and radio equipment on land can also be used in shipboard DC and AC equipment. Some devices are readily available from electronics stores. Radio antennas can be protected using lightning arrestor hardware designed for cable TV.
Connect the "ground' connection to the lightning grounding network. AC transient protection outlets or plug-in metal oxide varistors MOV work also on boats but need to have their ground connections connected to the shore ground wire.
Ideally this ground should also be connected to the lightning protection ground but this circuit arrangement can cause ground current problems in marinas.
As for protection of DC electronics, which are probably the most important, transient protection devices are available to clamp voltages at the point where each piece of equipment is connected to the DC supply.
These are available from companies such as General Electric or from mail order electronics distributors. They can be found under the generic name "Transient Suppressors" and are of various types: metal oxide varistor, silicon avalanche diode, and surge suppressor zener diode. It is important to locate this protection device immediately next to the equipment and each piece of equipment should have its own device.
The overvoltages that appear at DC inputs can be reduced by using twisted-pair wiring in wiring harnesses, ideally with a conducting sheath that is connected to the bonding system. The overall philosophy here is to minimize the spacing between positive and negative DC lines.
If a main control center exists, surround it with a conducting enclosure that is connected to the bonding system. Through-hull transducers are especially vulnerable. Due to the typically vertical alignment of the cables connecting these to their main electronics, they should be regarded as being part of the lightning grounding system.
Since the wires used in these cables are of an insufficient thickness to withstand a lightning strike, a 4 gauge copper wire should be placed parallel to any cable that leads to a through-hull transducer. The top of this copper wire should be reconnected to the lightning grounding system and the bottom to a ground strip close to the underwater transducer on the outside of the hull. Disconnecting equipment in advance of a storm helps isolate it from voltages induced by lightning, and the larger the lead separation the better.
Use disconnects in preference to knife switches, and these in preference to switch panels. Personal Safety Consider the worst case scenario for a lightning strike to a sailboat - a small boat in fresh water. If the boat has been provided with a well-built protection system it is still an exceedingly hazardous situation.
If lightning protection does not exist, the situation is life threatening. In both cases, the areas to avoid are close to the waterline and close to large metal fitting. In the unprotected boat, an additional -danger zone is beneath the mast or boom. Even in the unprotected boat, it is unwise to get in the water, as electrocution is highly probable if lightning strikes nearby.
In fact, there is no safe place on an unprotected small sailboat, and in a protected boat only places of relative safety. There is, however, one place that is more hazardous than a small unprotected sailboat, that is a small unprotected boat without a mast.
Every year there are multiple deaths of boaters in open boats caused by lightning strikes, but very few reports of sailors in sailboats killed by lightning. The above general rules also apply to larger sailboats. These are generally safer, if protected, since it is possible to get away from the waterline and large metal objects, and yet still stay dry inside the cabin.
As far as unharnessed electricity is concerned, a dry human body is much less attractive than a wet one. When the strike exited the cable, it had no easy way to get to the water. After traveling a quarter of a mile through air, lightning has no trouble going through a fiberglass hull, and this is exactly what it did, blowing a 3-inch hole on the way. Fortunately, the hole was above the waterline, and the boat was saved from sinking.
Powerboats are also susceptible to hull damage and are less likely to have been fitted with a lightning-protection system. Fortunately, the strike usually exits the boat through the props and rudders, and aside from damage to the bottom paint, the running gear is not often damaged although electronic engine controls sometimes are.
Need another good reason to replace a leaking fuel tank? A foot fishing boat with a small amount of fuel in the bilge exploded at the dock when it was struck, sending the contents of the boat's cockpit nearly feet away. Rarely, the claims files show that lightning enters a boat's electrical system and creates enough havoc to start a fire. One component that is often destroyed is a ground fault circuit interrupter GFCI.
This can easily be overlooked after a strike. Though it may still power appliances, the protection circuit is often nonfunctional. A GFCI can be easily checked by pushing the test button on the cover. Other small items to check are handheld radios and GPS, bilge pumps, inverters, lights, and fans. It should be noted that lightning is fickle and boat damage varies enormously; one owner saw his boat struck on the mast and yet none of the electronics were damaged.
The only evidence the surveyor could find of the strike was a blackened area on the masthead. He often writes local news items for BoatUS Magazine's Waypoints column and contributes to Reports, in-depth tech features in every issue written to help readers avoid accidental damage to their boats. Coast Guard license.
He lives in California. We use cookies to enhance your visit to our website and to improve your experience. Membership Search. Service Locator. Get a Quote.
Become a Member. Renew Membership. Get the fire extinguisher - Fires are uncommon, but make sure you have it at hand. Stay down below as much as possible - If you're not needed above deck, or if you've decided to sit it out, stay below deck.
This will be the safest place in case there's an impact. The hull will act as a sort of Faraday cage not entirely, but close enough. Unplug all electronics - Now that you've secured power and control over the boat and yourself, it's time to worry about your gear. Unplug all electronics - I mean physically pull the wiring out of them. Put small electronics in the oven - I think this is just superstition, but some people say you should put all loose electronics inside the oven to protect them.
You probably could give it a try, there's not really anything better to do. The DIY method: create an easy path for the lightning by taking a piece of anchor chain. Wrap it around the mast, a cap shroud, and then take the end and place it in the water. This creates a kind of earth return, which is said to prevent lightning strikes. The PRO method: You can install an electrical charge dissipator in the mast head.
It looks like a brush. It will avoid the impact to be drawn down by the mast. If you're interested, I found this one on Amazon with great reviews and for a good price. Quick tip: One of the most likely and worst things that can happen after impact, is finding yourself without a means to navigate.
Lightning can easily destroy your GPS, and even flip your compass around. You may consider getting a small backup GPS receiver that runs on batteries. If Store it separately and away from any metal parts. If you're interested, I found this one by Garmin on Amazon with good reviews and for a great price.
You can use it to store waypoints, like the harbor entry and shallows. In my opinion the best backup. We were almost one week in. It started out as a quiet night. We were at anchor at a peaceful, small lake next to the IJsselmeer. Halfway through our bottle of wine, the boat started rotating around the anchor.
We climbed out of the cabin. We were spinning around at a high speed, and everywhere around us, flashes of lightning came down crashing from the sky. We were the only sailboat on the lake at that time, and it was frightening, to be honest I was still young.
We phoned up a friend, hysterically, and he checked the weather forecast for us. I remember screaming at him, fearing for my life, 'what way does the storm move?!
0コメント