Boom angle is very important for any mainsail furling application. whether it is an in boom furler or and in mast furler, retaining the correct boom angle is vitally important to keeping the system functioning correctly. we recommend setting your boom height and leaving it. if you like to constantly adjust your boom vang, boom topping lift etc... we always tell our customers to mark the lines accordingly so the correct boom height can be easily re-achieved. you want to be evenly pulling on both the leech and foot of the sail when deploying an in mast furler. we commonly find the boom height too low and by adjusting it to the correct angle the sail rolls in and our effortlessly. as a general rule of thumb, we set the aft end of the boom at a height so it matches the same height as the tack. in other words, if you were to draw a line or pull a string from the tack of the mainsail to the back of the boom this line would be at a 90 degree angle to the mast. depending on the system, there can be some further adjustment required to obtain the exact correct angle. battens are always problematic in these systems and we always recommend removing them. once a sail gets old and stretches it is more likely to start jamming in the mast.

Thanks David . Very useful answer. Plenty for me to work with. I think my sail shape is still okay so hopefully can leave the battens in .

That is a great question! While both systems have their advantages and disadvantages, we see more in mast furlers than in boom furlers. Both systems work equally well when setup and used correctly. At the end of the day it comes down to personal preference and proper setup, use, and maintenance.