My mast step has no contact with a keel bolt. I have 4 gauge wire from the mast going to a keel bolt. I make it take a radiused turn, any right angle in a ground is bad and a place the lightning may jump off of. Joe Coquina C&C 35 MK I
-----Original Message----- From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Robbie Epstein via CnC-List Sent: Friday, June 28, 2019 2:52 PM To: cnc-list@cnc-list.com Cc: Robbie Epstein <repst...@embarqmail.com> Subject: [EXTERNAL] Re: Stus-List keel bolt nut My $.02 worth from someone who took a direct lightning strike year before last. On my 40-2, the mast sits in a mast shoe, really a box made of 1/4" aluminum, that has two keel bolts attached through it (one directly under the mast itself). I had a small 12 AWG wire that connected the mast to the mast shoe, through tapped holes in each. After the strike, it was clear that the vast majority of the strike energy made it to, and through, the keel as the bottom paint on the keel looked like a million little pock marks blown through the paint. I also had a couple of small holes in the rudder, but no holes through the hull. The 12 AWG wire was still in place and not burned. After stepping the mast, clearly the direct contact of the mast with the mast shoe, directly bolted to the keel was the main conductor. The mast bears on the shoe with probably at least 2000 lbs of force from the standing rigging and therefore will make quite good conduction, even if the lightning has to jump a mil or two of paint that was originally in between. This will be by far the path of least resistance. Realistically, after the mast has been in contact with the shoe and the boat sailed, there will be contact between the mast and shoe anyway after a while. You can test this with an ohmmeter and verify that for yourself. The main reason I can see for bonding the mast with a wire to the keel is as a safety measure to ensure that under all conditions there is a path to bleed static discharge from the mast to ground, hopefully averting a strike altogether, and possibly help shunt energy from a nearby strike. The point is, once lightning strikes directly, it will go to the keel anyway if the mast sits in a shoe bonded to the lead keel. If this is not the case, like in the case of a deck stepped mast, then the largest bonding wire available between the mast and the keel would be advisable. BTW nothing you do will convincingly protect your electronics from a direct strike. With billions of volts and tens of thousands of amps being drawn, the field generated alone will probably fry the electronics anyway. Add that to the fact that you have wiring connected up the mast to lights and probably wind instruments, it's going to go all over the electrical system anyway. One of the changes I made after the strike was to run all the mast wiring connections through quick disconnect connectors at the base of the mast that I disconnect after every sail. I don't know that it will make a difference, but it certainly can't hurt! Just my $.02 worth. Robbie Epstein Thorfinn, C&C 40-2 TMDK Fort Walton Beach, FL _______________________________________________ Thanks everyone for supporting this list with your contributions. Each and every one is greatly appreciated. If you want to support the list - use PayPal to send contribution -- https://www.paypal.me/stumurray
