My magnets to secure the solar panel came today, accompanied by one of the scariest health warnings I've ever seen!! The four page leaflet includes all sorts of danger warnings, including detailed description of what can happen to your fingers if trapped between two big neodymium magnets. Only hydraulic cramps can pull them apart.
My magnets however are relatively safe, being ferrite and having a pull of 18kg each. That should be enough for four of them to secure a solar panel on a steel roof. Neodymium magnets of the same size would have a pull of 6okg each. Try pulling them off the roof. As for the next size up, they pull 155 kgs! These are seriously dangerous objects and have to be kept at least 500mm apart. They will sever your fingers, stop your watch and your pacemaker, wipe your credit cards etc from some distance.
I will have to use stainless steel screws(relatively non magnetic) to attach them to the panel and I suppose I may need non magnetic screwdriver/ spanners too in order to fit locking nuts. Hmmm.
I can see that I will need to be very careful in putting them in position on the boat roof. Apparently the idea is to put a plastic or nylon spacer in between the magnet and the steel surface and then slide it out when in position. I think I'll make a wooden handle to lower the magnet down on its screw.
Meanwhile I await the man delivering the solar panel.