Mike Dolt Enterprises
Mike Dolt Enterprises
User: jkcowboy
Asked on: Friday, March 25, 2011 at 2:27 pm EDT
Answered on: Tuesday, May 14, 2024 at 3:16 am EDT
Question: I have a 28' Corsair folding trimaran with all plastic/FRP hull in contact with the seawater (i.e. the mast is not electrically connected to the water). Historically these boats have not been struck by lightning while on the trailer with the mast raised but... on the water they have been struck. The strike generally carries down the SS shrouds to SS chainplates that are located about 12" inches from the waterline. From there, the strike is quite destructive, generally punching 1/4" holes thru the hull delaminating FRP as it goes. I'm trying to bond the mast to the water using NFPA and ABYC standards in the system design. My limitation is that I do not want to bolt a 100 sq in copper plate to the hull for drag purposes (race boat). So, I'm thinking of using a temparary system of heavy guage copper plumbers tape (7' long, > 100 sq in exposed surface area) with lots of edges towed thru the water by a #8 Cu THHN wire bonded to the mast with a lug.My questions is two fold: one general comments on whether the temporary system would work and improve the situation, and two... how good of an electrical connection would I need to make to the mast? I would like to install a bolt on lug to the mast and am questioning which materials to use? Al, SS, Cu Lug? Al, SS, Cu Bolt? The mast is 3/16 extruded aluminum section. Also trying to minimize any galvanic corrosions between the mast and the lug. My best guess now is Al mast -> 3/8" threaded hole ->Al bolt -> Al lug to copper wire.I'd appreciate any tips/advice.John
General Comments on Temporary System
Using heavy-gauge copper plumbers tape towed through the water could potentially improve the situation by providing a path of least resistance for lightning to follow. However, it is important to note that it is not a permanent solution and may not be as effective as a properly designed and installed lightning protection system. The temporary system should be used only as a stopgap measure until a more permanent solution can be implemented.
Electrical Connection to Mast
A good electrical connection is crucial for an effective lightning protection system. The best material for the lug and bolt will depend on the specific mast material and its electrical conductivity. For an aluminum mast, it is generally recommended to use an aluminum lug and bolt to minimize galvanic corrosion. The bolt should be appropriately sized for the lug and mast thickness, and should be properly tightened to ensure a good connection. A stainless steel washer between the lug and mast can further improve the connection and reduce galvanic corrosion.
Recommended System Design
Based on your requirements and the information provided, the following system design is recommended: Use a 3/8" or 1/2" diameter aluminum lug with an appropriate number of holes for the copper wire. Drill a 3/8" or 1/2" diameter hole in the mast and tap it with the appropriate thread size. Insert an aluminum bolt with a stainless steel washer between the lug and the mast. Tighten the bolt to the specified torque for the bolt size and material. Connect the copper wire to the lug using a crimp lug or solder connection. Ensure the copper wire is securely attached to the lug and has sufficient slack to prevent it from being pulled loose during a lightning strike.
Additional Tips: Consider using a grounding plate or strap to connect the mast directly to the water. This can provide an additional low-resistance path for lightning to follow. Inspect the mast and lightning protection system regularly for any damage or corrosion. Consider consulting with a qualified marine electrician or lightning protection specialist for further guidance and assistance. Flag for review