Geronimo,
Hayden is correct. As per the original design shown in the IP 27 Owners Manual (available in the file download area on the IP Home Port website), there is no ground bonding wire to the mast step and, in fact, the mast head is grounded only through the starboard shrouds chainplate and the starboard backstay chainplate.
I believe the mast grounding system for later IPs remains much the same. Certainly our 380 bonding system has green bonding wires for mast grounding going only to the port shrouds and backstay chainplates. It's not clear to me why the mast step is not grounded and also why the starboard backstay and shrouds chainplates and the headstay fitting are not grounded, but that's as Bob Johnson intended.
It may be of interest to know that, at least for us, the grounding system as designed has saved the boat from catastrophic lightning damage. Last month while on our mooring on the Chesapeake we took a direct strike to the masthead that destroyed the VHF antenna and windex, then apparently traveled down the VHF coax cable, the grounded port upper shroud, the grounded port backstay and also the headstay and genoa foil (not connected to the bonding system, so not clear where the current ended up), and then apparently largely via the bonding wiring system to ground (i.e. sea water) through the bronze hull fittings, propshaft and propellor. There is no visible damage to the hull, chainplates, or interior, but there was direct damage (heating or arcing) or indirect damage by voltage surge or induced currents to some standing rigging, all electronics, and much of the electrical equipment and systems. Even the house and engine batteries, refrigerator compressor, and bilge pump float switch were damaged. Total diagnostics and replacement parts and labor exceeds $40,000. I can provide a list of the repair/replacement work needed if anyone is interested.
The good news is that we now have a lot of new equipment and standing rigging and great new communications, navigation and sailing instruments - all covered by our insurance. It may also be of interest that our insurers covered the claim 100%, new for old, with no deductible and no depreciation. Certainly a recommendation from us for insurance from Boat US.
Graham
Graham Jones
IP 380 Indigo
West River, MD