This isn't really a new topic, but I have been in contact with Barton regarding the double block at the top of my keel hoist. One sheave broke into 3parts and shed all its bearings, the other is cracked across. I am assuming from the lack of response to my first mail, no-one else has had this problem as yet. Barton tell me that their ball bearing blocks are not suitable for static loads. Since I have owned Shivra she has been dry sailed, so the only time the blocks have been under load is during launching, since I've not used a drying anchorage or mooring,yet this has happened.
Incidentally PBO did a test on blocks a bit ago, and found little difference in performance between plain and roller bearing Bartons.