With heavy thunderstorms you will often find lightning. Lightning on the water can bring life-threatening circumstances. For your safety and the safety of others aboard your vessel, this week’s edition of Shippers’ Guide is publishing this article on lightning protection to help you understand what to expect during a thunderstorm and how best to handle the weather while at sea.
Protect Yourself: Even though the odds are in your favor that your boat may never be hit by lightning, if it happens it can have devastating effects. Don’t take a chance, shelter yourself.
If you are in a small boat and close to shore when a thunderstorm approaches, get in and off the water immediately. Better yet, don’t go out if thunderstorms are predicted. But what if you are miles offshore and a storm pops up? Hopefully, you have prepared in advance.
The voltages involved in lightning are so high that even materials that would normally be considered non-conductive become conductors, including the human body. The voltages are so massive that if they start to travel through a boat’s structure – say through its mast – then meet with high resistance (for instance, the hull skin) the current discharge, in its attempt to reach ground, may simply blow a hole in the non-conductive barrier.
The safety conscious Captain should make sure that his vessel is properly protected. Reference should be made in detail to the standards for lightning protection and the job should be performed by a licensed marine electrician.
Lightning Protection System: In theory, a lightning protection system is used to create what is known as a “Faraday’s cage,” so called after the late nineteenth-century scientist Michael Faraday. The principle of a Faraday’s cage is to provide a surrounding, well-grounded, metal structure, in which all of parts are bonded together and carry the same electrical potential. Such a “cage” attracts and carries any lightning strike to ground much like lightning rods on buildings.
In other words, you need to provide an unobstructed way for the lightning to dissipate its energy to ground (the water surrounding you). Faraday himself risked his own life to prove this theory. The additional benefit of a lightning protection system is that it tends to bleed off any charge build-up in the general vicinity, possibly averting a lightning strike in the first place.
So how does a lightning protection system work? In a ship, the “cage” is formed by bonding together, with heavy conductors, the vessel’s mast and all other major metal masses. A marine electrician must tie in the engines, stoves, air conditioning compressors, railings, arches etc. with a low resistance wire which would ultimately provide a conductive path to ground (the water) usually via the engine and propeller shaft, keel bolts, or better yet, a separate external ground plate at least 1 square foot in dimension.
It is important that you ensure that your crew fall within the protection of the “cage,” something not always feasible when the vessel is not built of steel or aluminum. On fiberglass or wooden boats it is advantageous to have a mast or other conductive metal protrusion extending well above the vessel, creating what is known as a “cone” or zone of protection.
It is generally accepted that this cone of protection extends 45 degrees, all around, from the tip of the metal protrusion. This means that if the aluminum mast of the average sailing vessel is properly bonded to the vessel’s other major metal masses and is given a direct, low-resistance conductive path to ground, the entire boat should fall within the protected zone.
If the vessel has a wooden or composite mast, a marine electrician can achieve the same effect by installing a 6 to 12 inch metal spike at the top and running a heavy conductor down the mast and as directly as possible to ground, usually through the engine and propeller shaft. Have a professional marine electrician install your lightning protection. This is not a do-it-yourself project.
Preparation For Heavy Weather: This week’s tip is all about preparing yourself for heavy weather. If you have kept a proper lookout, developed a “weather eye” and monitored the weather on your VHF radio, you should have plenty of time to get prepared. Obviously, the best way to handle rough weather is to get to shore immediately and avoid it completely. However, this may not be practical if you are on an extended cruise. In this case, you should prepare yourself, the vessel and your crew for what is to come.
As boats vary in design and size, and weather conditions vary in severity, so does the laundry list of precautionary items that need to be performed. The following list was accumulated from various resources and from input from those who answered last week’s question concerning “what to do if heavy weather is approaching.” Thanks to those who contributed. For novice boaters we have defined some of the, perhaps, unfamiliar terms such as jack line, sea anchor and drogue below.
What Every Skipper Should Know: Meet with the crew to explain the situation and reassure them. Make sure that they know what to do, and what not to do, when the extreme weather arrives. Explain such things as keeping low in the boat, not moving around excessively and not going out on deck unless necessary. Give them all an assignment to keep them occupied and keep their minds off the situation.
Determine position of storm, wind direction, speed and estimate time to your location; Secure all hatches; close all ports and windows. (Keep the water on the outside; Secure all loose gear above decks and below.
Put away small items and lash down larger ones. Anything you want to have when the storm passes must be secured.
Break out foul weather gear and exercise your authority as skipper by requiring them to be worn by everyone on board. Do this before the weather gets bad, don’t wait too long; Ready emergency equipment that you may need such as hand pumps, bailers, first aide kit, sound signaling device, etc.
Get a good fix of your position and plot it on your chart. Make note of the time, your heading and speed; Make plans to alter course to sheltered waters if possible; Continue to monitor your VHF radio for updates to severe forecasts; For extremely severe weather, break out your abandon ship procedures and review them.
Make sure the life raft is ready to be deployed; Make sure emergency food and water are in the life raft; Rig jack lines (see below for definitions) and/or life lines and require anyone who must go on deck to wear a safety harness.
Make ready your sea anchor or drogue if needed; Turn on navigation lights; Keep away from metal objects; Change to a full fuel tank if possible; Keep a sharp lookout for floating debris and other boats; If you have a choice, do not operate the boat from the flybridge.
Jack Lines – lines rigged along the outboard decks running from the bow aft. This allows you to attach the tether from your safety harness and move forward and back at will.
Life Lines – usually vinyl or plastic covered wire rope at the sides of the boat’s deck to keep the crew from falling overboard.
Safety Harness – a nylon web harness worn in rough seas or heavy weather. It has a tether with a clip. The clip is attached to the jack lines or lifelines so that if you are washed overboard in a storm you are still attached to the boat.
Sea Anchor – A floating canvas cone, held open by wire rings, with an opening in the smaller end, and a rope bridle at the larger end attached to a line leading to the bow of the boat. It is used in storm conditions to (a) keep the bow of the boat into the wind, and (b) slow the downwind drift of the boat.
Drogue – Any device steamed astern to check a boat’s speed and/or to help keep the stern perpendicular to the waves in a following sea.