Inject about half-way up!
Pencil the 'must-do' list with other c/line bolts. Do the easy ones first,and that will give you an idea how hard/easy it is to get them out, and their condition.
When you want to move a sleeper you can jack the boat up until its clear by a few mm, then put in another block close too. Wedge it up and remove the original block. As you let the boat down free off the shores. Another person helps doing this.