Many of the skills in the BC Boilermakers apprentice manual are not easy to practice, as the equipment is not readily found. These efforts create opportunity for the future. Many of my skills I do have started in this way - making a lone effort and finding someone with experience to "show me the ropes" (!) at the time the skill became useful.
Block-and-tackle and how to reeve one. No-one had any I could try. So I got a "Meccano" set and practiced with a model version. I can now reeve up to a 3-by-3 block-and-tackle without having to look at a manual. Although difficult to describe in words or diagrams, the order makes plain and simple sense after you've tried it a few times.
A Stiffleg Derrick is said to be very efficient. Using "Meccano" again, this one proves the case - it will lift many times its own weight. I found how a stiffleg derrick behaves at various angles of luff and swing - and how much ballast you need if you weight down the derrick - rather than bolt it to the floor which is often the preferred solution. (The structurals should be straight but I ran out of straight pieces!)
Seeing eye-splicing a wire rope with a thimble in the eye caused me to think of applications where putting the same type of thimble in a fibre rope would be beneficial. This has already found application - see rigging section