Re: New mainsheet - recommendations
Are you also moving the mainsheet attachment on the boom forward? If so you could probably get away with a slightly shorter mainsheet. I'd still probably purchase 50', it's better to buy too much and cut off 5' then to buy too little and need to buy a longer one.
You can also just measure. Put the boom at it's farthest point forward (against the shrouds) and measure the distance from your traveler to the block on the boom. Multiply by 4, add about 5' for bowline, stopper knot, and excess to grab, and call it good.
I wish the Catalina 25 were better setup to have a traveler in that location. The stock one is a joke, but putting one up there makes a terrible tripline for people going below.
Do you plan on cutting the boom shorter? It's only so long to allow for end-boom sheeting.
1986 Pearson 28-2 "Elena"