preventer on a 272 O'Day

[Merilyn]

I recently bought 1/2 interest in a 1987 272 O'Day on the Chesapeake. The other 1/2 has owned his share for 12 years but has never taken formal lessons and is quite limited in sailing ability, especially now that he is developing dementia. There is a block and tackle preventer/boom vang attached maybe less than 1/4 way on the boom from the gooseneck. This preventer is movable to travelers on the deck on both port and starboard midship. To change it, you must go up on deck and pass it across under the boom to someone else on the other side of the deck. Currently their method of sailing is to move it back and forth sort of randomly. Obviously, they do not change course very often.

Everything I have read indicates the preventer that requires getting on the deck to move is more dangerous than the possibility of an accidental jibe boom hit, since you're right up there under the boom. I just completed ASA 101 basic keelboat sailing with MD School of Sailing and am eager to practice, but we don't know how to handle this preventer. Last time out, we just loosened it, but then the boom tends to ride up, since it also is used as a vang. Is this type of preventer typical of an O'Day? My only other experience was with an O'Day Day sailer (17) and it didn't have it.

I can't see any possibility besides moving it across before every tack, unless we could somehow bring it back to near the mainsheet, which I have no clue how to do.
Please help if you are able. 2 pix are included to help explain.Merilyn

 

[Richard19068]

Is there something to attach it to at the base of the mast to just use it as a vang and not a preventer? It looks to me like that is what it is and somebody just set it up to be able to be used as a preventer when needed/wanted. If so, just hook it up to the base of the mast and use it as a vang. It's not that often that you really need a preventer.