Sailing in a thunderstorm

[SEMIJim]

Originally Posted by saurav16

yeah motoring sounds like a plan but what about lighting?

There's really not a lot you can do about it but pray. camaraderie's #1 and #2 suggestions are valid. (#3 is arguable--but let's not). Thing is: Lightning isn't going to strike your mast unless it was going to strike w/in a circle the radius of which is equal to the height of the mast, anyway. So, if you have, say, a 40' mast, you're only going to attract lightning for a 40' radius around you.

Jim

[danlindstrom]

Has anyone on this board ever heard of anyone being seriously hurt or killed by lightning while sailing? I haven't. People get killed by lightning in their homes and on Terra Firma all the time. Sailboats get hit by lightning every day (most of them unoccupied), doing tremendous damage to electronics and even blowing holes in hulls, but where are the statistics on sailors getting hurt by lightning?

If your rigging is properly grounded, you're in a "Faraday cage" protected by your shrouds, stays, mast, and boom. It's a far, far safer place to be than, say, jumping off your boat onto a metal pier while seeking safety. I suspect the major health risk to sailors from lightning is having a heart attack from worrying too much about what empirically appears to be just a small risk. So ground your rigging and if you're caught in a storm, do what needs to be done to ride it out and don't worry about the lightning. It will pass. If you're still worried about lightning, go with the statistics and give up golf!

[sailingdog]

dan-

Unfortunately, most boats aren't sold properly bonded and grounded for lightning. And there are two schools of thought on this... a grounded boat is more likely to get hit than an ungrounded boat, so some people don't ground to reduce the chance of getting hit. Others, believe that a grounded boat will take significantly less damage, and weigh that against the risk of getting hit a bit more often.

[nk235]

In terms of grounding, how do you actually do this? I know I spoke with some people in my marina and they say they attach a piece of wire from one of the shroads and let it fall off into the water as the ground wire. Is this o.k. to do or are there better practices out there for grounding a boat.

[sailingdog]

The people in your marina are deluding themselves into thinking they're protected... they're not. Shrouds and stays, made of 316 stainless steel, are very poor conductors of electricity, and the connection of the wire to the shroud is questionable at best, given the amperages we're talking about here. The wire's bare end trailing in the water also doesn't provide enough edge for it to act as a good boat-to-water grounding surface.

Ideally, you should have a heavy (4 AWG or heavier) wire running down from your mast, which acts as the primary lightning path on most boats since aluminum masts are fairly decent conductors of electricity, and down to a bolt or stud that attaches to a metal plate faired into the hull. The plate should have four linear feet of edge at a minimun—a 1' x 1' plate would do, but a 2" x 2" plate would be better—to dissapate the charge into the water.

The conductor connecting the mast and the stud should have as straight a path as is possible, since lightning doesn't like to turn corners. If you also bond the shrouds, stays, chainplates and stanchions to the same plate, it will create a "faraday" cage for the boat made of the standing rigging, and that should protect the passengers on-board from a direct strike.

YMMV... on some boats this works well, on others, not so good... If you have an external bolt on keel, the keel can often be used for the lightning ground surface—but only if it is external. Doing so with an encapsulated keel is a really bad idea.

[eherlihy]

According to Chapman: " A measure of lightning protection can be obtained using the principle of the "Faraday Cage." A high pointed conductor, heavily wired to all points of the boat, seems to cast a cone-shaped umbrella in which lightning does not strike. Instead, the voltage is conducted safely to "ground" in the water via submerged metal parts such as the rudder, sailboat keel, or propeller."

[Sailormann]

Quick question: is there any special procedure for sailling in a thunderstorm ?

Avoid it. If that's not possible, reef early and make sure the engine's ready. Make sure that you keep the bow (or the stern) facing the waves. Don't leave a lot of things loose in the cabin - especially in a small boat. If there are enough of them, and they are heavy enough, your boat may become unstable. Enjoy !

[sailortjk1]

Lightning is the one thing that you can do very little about.

The discussions of Grounded versus not Grounded are sound disscissions.
We can and have debated this at length.

But when you are out there on the water and you get caught in a lightning storm, what can you really do? Not a whole lot.

If the wind is overpowering, we know what to do, we have a plan of action that we persue. But when we get caught in the flash storm, in all seriousness, we are taking our chances and simply must ride it out.

Maybe the more important question is, do I have a plan in place if I do get struck? Do I have plugs on board? Where should the crew be placed? Etc..

During a lightning storm about three years ago, I look down below and my daughter is comfotably sleeping in the main saloon, RIGHT NEXT TO THE MAST SUPPORT. I quietly went below and suggested that she sleep in the aft berth untill this blew over.

If your going to be out cruising, its enevitable that its going to happen sooner or later. Try to carefully watch your weather window and use your best judgement.

[sailingdog]

Originally Posted by eherlihy

According to Chapman: " A measure of lightning protection can be obtained using the principle of the "Faraday Cage." A high pointed conductor, heavily wired to all points of the boat, seems to cast a cone-shaped umbrella in which lightning does not strike. Instead, the voltage is conducted safely to "ground" in the water via submerged metal parts such as the rudder, sailboat keel, or propeller."

Yes, but if the keel, rudder or prop aren't connected directly to the mast, via a relatively heavy conductor, chances are very likely that the lightning will sideflash through the boat to get from one to the other. This is more the case with a deck-stepped mast, than a keel stepped mast, especially if the keel is bolted to the mast step.

A Faraday cage requires that the pieces of it be connected electrically... if they are not, no Faraday cage is present.

[donradclife]

We put the portable electronics in the oven ( a microwave is even better).

If you have radar, you can track the cells, and try manuevering to avoid them, but its hard to predict their patterns--sometimes you miss the cell you were worried about, and get slammed by a new one.