Joe Nieters of Dillon, Colorado, asks:
"What are the advantages of a rigid boomvang? Many boats I’ve seen with them seem to also have topping lifts, and a lot of the rigid vangs also have a block-and-tackle control arrangement."
Win Fowler replies:
The advantage of a rigid boomvang is that it supports the boom. Having a topping lift and a rigid vang is a bit like wearing a belt and a pair of suspenders. Although the redundancy increases safety margins (you certainly don’t want the boom to fall on your head or your dodger when you are putting in a reef), I have to say it is rare to hear of a rigid boom vang that has failed.
Vangs come in two basic flavors, hydraulic and mechanical, and their primary mission is to keep the boom from falling down or rising up. If the boom rises up, the mainsail will twist excessively. This happens when the boom goes past the outer end of the traveler, and the mainsheet loses its ability to hold the boom down.
Hydraulic vangs often use compressed air, while mechanical vangs generally rely on a spring to support the boom and keep it aloft. This is a useful feature in light air, when the weight of the boom can prevent the sail from twisting.
You can get a similar result using a topping lift, but it’s not as convenient and it can’t be adjusted as quickly. A topping lift also has a tendency to chafe the leech of the mainsail.
The spring in the mechanical vang on my 36–footer allows me to adjust boom height easily, even when there is tension on the mainsheet. When lowering the mainsail I use the vang to pull the boom down to a point where it is easy for me to flake the sail on the boom. Once the sail cover is on, all I have to do is to ease the mainsheet and the spring in the vang raises the boom back up over my head.
When I leave the boat and go ashore, I always attach the main halyard to the end of the boom and tension it. I do this not because I fear the vang will fail, but because the flex in the vang’s spring allows the boom to move a bit too much.