Every sailboat in Florida should have as much lightning protection as possible. That being true, no reasonable lightning protection system is guaranteed to prevent lightning strikes or provide complete protection if your boat is struck. After boiling down all the options and getting valuable design input and insight from Wizard, I installed this lightning ground strip in the Tridarka Raider.
I used an 8 foot strip of 6061-T6 aluminum 1/8" x 1" as the ground strip. If you do any research of lightning protection you will find that 1 square foot is a recommended minimum so this is a bit short, but I didn't want to go longer for many reasons. Everything is a trade off. My goal for this system is that the 8 foot strip is more than enough to bleed off any building charge and prevent the strike by keeping my boat "invisible" to the charge building in the clouds. If a strike does occur, the grounding strip should at least help a bit. Let's hope I never find out. A side benefit is that it serves as a rub strip for the deepest section of the hull.
The ground strip is connected through the boat at the mast step. It was painful drilling through the hull. This is the first of 7 holes along the keel.
I had to buy a 16" long drill bit for the first hole because this one had to come from the top for precise location inside the mast step. You won't have this additional expense if you drill these holes before installing the floor.
The oversize hole is then filled with high density filler. After this cures another hole is drilled for the 3/8" bolt. I used aluminum bolts, washers, and nuts to help prevent corrosion. Stainless bolts could be used but then corrosion would be faster. I only did this drill, fill, and redrill at the first hole -- all following holes were drilled with 3/8" only. Again, I had my reasons. If you do this before glassing it might make sense to drill, fill, and redrill for all the holes.
In order to install the strip I had to raise the vaka up high enough to crawl underneath and use a drill. It turned out easy enough to do -- and I'm happy to report I can still lift each end by myself. This is the stern held high in the form by a 2x4.
I did a similar thing at the bow, but had to add a strap to keep the boat from tipping to the side. I also put a couple blocks of wood on the other side so everything would stay in its place.
Here's a view of the whole vaka in the raised position. I had to raise and lower the vaka a few times during this procedure and this arrangement worked very well.
The aluminum strip has to be prepared. First, drill all the holes with a 1/8" pilot hole. I drilled a hole about 1 inch from each end. Then the other holes were drilled on 16" centers for a total of 7 holes.
Now drill each pilot hole with the 3/8" drill. Eventually these holes have to be counter bored for the flat head screws, but don't do that yet. First, bolt the first hole to the mast step and tape the strip into position. Like this -
The strip is bolted at the mast step along with a short piece of aluminum that serves as the contact plate for the base of the mast. The bolt/nut serves as a locating pin for the mast base and prevents rotation of the mast. At this point, don't use any sealer, because it all has to come apart before the final step.
With the first hole of the strip firmly bolted in place, the rest of the strip is held in place with duct tape - align carefully with the keel. Use the 3/8" holes as guides to drill through the hull from the bottom. First drill the hole closest to the mast step. Then bolt is place. Then drill the next in series: drill, bolt in place -- drill, bolt in place, etc. It is important to drill and bolt in series because the aluminum strip will tend to sag. If you do it in some other order, you will have problems.
Once all the holes are drilled you will want to coat any exposed wood with epoxy. While that is soaking in take the strip back to your table and clean it up real good. Use a counter bore bit to bevel the holes so that your flat head screws are flush. Use 40 or 50 grit sandpaper and a file to rough up the surface going next to the hull.
I used EZFillet to coat the mating surfaces.
This looks a lot rougher than it is due to smeared epoxy. Also the screw really is flush - the squeezed out epoxy makes it look high. Again start at the mast step and use duct tape to hold the strip in place as you work your way to the other end. I had Tim the Carpenter help me at this stage. I put 3M4200 on the threads near the head and pushed it through the hull. Tim put 3M4200 on the washers and nut and then held the nut while I tightened the screw from below.
The fillet material should squeeze out and fill gaps all along the strip. But be careful to leave the edges exposed. The current is discharged mostly from the edges of the strip. This picture shows a bit of fairing fillet (it will be tooled off smooth later) at the mast step end to prevent the edge from snagging anything. But notice the rest of the edges are clean. I will do a bit more of low density fairing along the edges, but the bottom edge will remain exposed.
Here is the ground strip fully installed looking from the stern end.
I checked the resistance from the mast step contact plate to the ground strip and came up with 4 ohms. My meter hardly ever registers less than 4 ohms so it looks like a successful installation. BTW, be careful how you use the 3M4200 at the mast step bolt. I had Tim put it on the bottom of the contact plate but not on the washers or nut of the bolt. All other bolts, washers, and nuts got a liberal dose.
The final step is to cut the bolts off flush with the nuts on the inside of the boat. Then cover the nuts with epoxy putty and smooth over so they won't catch on anything. Don't do any of this to the bolt/nut inside the mast step - leave it as is.
I don't like having these bolts through the boat, but when lightning is flashing all around I will appreciate all the work that went into this part of the project.
I'll cover the mast part of the system when I get to that task.
