Allow me to go off a a tangent here, but this thread question started me thinking on a broader scale & I would like to offer some of my thoughts on boat familiarization.
I can understand questioning something you need clarification for on your sailboat. What I find puzzling in many "what is this" threads is a lack of general system/elec/mech. knowedge by owners. Newbies to the sport will have many questions and that is fine. But owners that have been at it for some time, one would think their knowledge should be more encompassing.
To give you an example, my boat neighbor of a beautifully redone Morgan OI 42 he asked me to look at his diesel engine as he had questions. When we went over the engine I discovered he had no idea of the simple mechanics and engine part or use. Where would he be if he had to troubleshoot and/make repairs while underway?
Sadly, I see this many times with skippers & try to help when I can. But, owners have an obligation along the lines of safety & preparedness as they are soley responsible for their passengers and boats.
Knowledge is power, and with this, confidence grows. My pal with the Morgan is a fine sailor, but beyond doing his teak, relies on other people/services for all else. This is a formular for problems down the road.
I suggest to others to start compile documentation/manuals/instructions/diagrams & spend the time to get a better understanding of the systems they use. As you compile this information, alot of what you will learn will jump out at you, as you will see.
Our sailing buddies are all of a special "club" and I find most eager to help a fellow sailor. Invite knowledgable folks on board, ask them questions, take notes, do some "hands-on" to gradually get to know your boat inside & out. This can almost be as enjoyable as sailing.
In a short amount of time, you will be happy with this new found knowledge and become a jack of all trades skipper. You never know when this knowledge may be required. This all comes under the heading of "the prudent navigator."
I am not singling anyone out, just simply trying to be a helpful boater.
CR