At the ceiling of the cabin of my project 26.5 just under the mast step is a threaded hole going into the step. I believe it had a machine screw in it with a terminal and a wire going down the compression post. Does anyone know what the function of this is? The mast wiring has its own grounding wire and there is no mechanical bonding of the mast to the step so it could not be counted on to provide a positive ground. The only other thing I can think of might be some sort or rudimentary lightning pathway. Thanks
Mast ground/Lightning?
- Thread starter Bruce Rowe
- Start date
Sounds like a lightning ground. Does the wire go to a keel bolt?
Lightning grounding is a can of worms. to ground or not and if you ground where is the best place.......
I'm of the opinion that if the clouds are one plate of a capacitor and the water surface is the other then your boat sits on the bottom plate and the mast sticks up above the bottom plate and the keel sticks below it. The nature of fiberglass is that it is an insulator so the natural tendency is for lightning to strike the mast and then move down till it is at the level of the water. at that point it wants to go horizontal and not continue downward toward the keel. It depends on the actual electrical insulation (air, hull, distance, people.....the boat layout) that is between the bonding wire at the water level and the water surface. It may be that the shortest path to ground is down to the keel then up to the water surface (note that the charge is only on the water surface and about 0.1" deep) or it may be for the current to jump to some other metal object near the hull and at the water line and then through the hull to the water surface.
So my solution is to keep the lightning out of the cabin altogether and put a wire from the shrouds, and stays over the side. A set of auto battery jumper cables works great. Cut them in half so you have 4 long heavy wires with a clamp on each. one for the port shroud, one for the starboard shroud, one for the forestay and one for the backstay.
Lightning grounding is a can of worms. to ground or not and if you ground where is the best place.......
I'm of the opinion that if the clouds are one plate of a capacitor and the water surface is the other then your boat sits on the bottom plate and the mast sticks up above the bottom plate and the keel sticks below it. The nature of fiberglass is that it is an insulator so the natural tendency is for lightning to strike the mast and then move down till it is at the level of the water. at that point it wants to go horizontal and not continue downward toward the keel. It depends on the actual electrical insulation (air, hull, distance, people.....the boat layout) that is between the bonding wire at the water level and the water surface. It may be that the shortest path to ground is down to the keel then up to the water surface (note that the charge is only on the water surface and about 0.1" deep) or it may be for the current to jump to some other metal object near the hull and at the water line and then through the hull to the water surface.
So my solution is to keep the lightning out of the cabin altogether and put a wire from the shrouds, and stays over the side. A set of auto battery jumper cables works great. Cut them in half so you have 4 long heavy wires with a clamp on each. one for the port shroud, one for the starboard shroud, one for the forestay and one for the backstay.
Masts and shrouds are grounded to divert static electricity which is a common occurrence. It is not designed to divert direct lightning strikes. check the archives on this subject. With so many sailboats out there, I repaired two in all my years and they were not hit direct. It is an often talked about subject, so check the archives.
Which boat do you think is most likely to be hit with lightening? One with a grounding system or one that does not? Chief
Both are equally likely to get hit.. it's what happens after the strike when the grounding makes a difference
Cheers,
Brad
common industry practice is to not take the lightning strike into the structure but to route it along the outside. Makes a lot of sense to me. whoever though that routing it into the boat living areas was a good idea should get struck with lightning IMHO.
Current tends to take the path of least resistance so, according to teaching on electricity, the grounded boat should be most likely to take the hit. Chief