Geoleo,
The vang and the boom
furler work as a
single system. The vang is a rigid vang that holds the boom at the proper angle (usually 88 degrees) to the
mast so that the boom
furler does its job without complaint or incident. It can be adjusted to change the angle but this is typically not done under way. Like everything else on a boat, this is a
trade off. If you are a
racer and will constantly pull on every available line attempting to get an extra 1/10 of a kt., then any kind of furler is a bad idea. For a cruiser, a 1/10 of a kt. is not nearly as important as having a relaxed, enjoyable and stress-free time. For me, peace and tranquility are important elements of cruising. Aventura will definitely go faster than the typical mono-hull of the same size, but it is not set up for
racing. Still, she will regularly do 7kt. under a decent
wind and I have seen 9+ kt. for hours at a time.
Mike