Mooring
Michel: You might check in Chapman's seamanship guide. Somewhere I have read that some used car engine blocks before there were laws and regulations about water pollution, and that after those worked into a muddy bottom they were quite sufficient. (I hope that they free of all oil, and presumably with all the accessories like carburetors, fuel pumps, valve and oil pans and starters etc, renoved i.e. down to the basic block). Anyway, I think you are talking about a few hundred pounds to match that, presumably of concrete or iron. You also need to know if there are permits required for your local mooring situation, suspect there are and that they would specify weight/substance requirements. Dick