Boom vang bail
Boom vang bail
Adding a boom vang to my 88 D. Can anyone tell me how far from the front end of the boom is the bail attached?
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Sisu
- Chief Steward
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Re: Boom vang bail
The vang should form a roughly 45 degree angle. Too close to the gooseneck = excessive stress on the vang, too far = more horizontal force than vertical.
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Tomfoolery
- Admiral
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Re: Boom vang bail
Here's a graphic I made some time back showing vang geometry and the resulting vang forces to generate 50 lb of force at 71" from the gooseneck hinge center. I don't remember if the vertical distance was measured, or eyeballed, or scaled from a photo. I could check it next time I'm at the boat if you like.
You can see that bringing the boom bail further out along the boom reduces the required vang force. It also reduces the bending moment in the boom, as there's less boom beyond the bail as well as a lower vertical component of the angled force. But there's a practical limit in that you probably don't want it attached at the end of the boom.
Also notice that the forces drop off fast with distance from the mast, but slow down with distance, so having it very far from the hinge doesn't reduce the vang force all that much way out there.
Just for fun, I scaled the numbers to a 1 lb vertical force at the end of a 10 ft boom, and included the vang force at the end of the boom, which isn't much lower than at 6 ft from the end, which just amplifies what I was saying about diminishing returns with distance from the hinge. But there is zero bending moment in the boom, other than what the sail foot may impart onto it, so there's that. Mounting the vang bail too close to the hinge can induce large bending moment in the boom, which is also why some mid-boom sheeting has blocks spaced apart along the boom underside rather than a multi-sheave block at one point. Lots to take into consideration there.
Oh, wonderful - looks like tinypic may be pulling a Photobucket. These may not open as large as I intended since I moved them to Imgur.
You can see that bringing the boom bail further out along the boom reduces the required vang force. It also reduces the bending moment in the boom, as there's less boom beyond the bail as well as a lower vertical component of the angled force. But there's a practical limit in that you probably don't want it attached at the end of the boom.
Also notice that the forces drop off fast with distance from the mast, but slow down with distance, so having it very far from the hinge doesn't reduce the vang force all that much way out there.
Just for fun, I scaled the numbers to a 1 lb vertical force at the end of a 10 ft boom, and included the vang force at the end of the boom, which isn't much lower than at 6 ft from the end, which just amplifies what I was saying about diminishing returns with distance from the hinge. But there is zero bending moment in the boom, other than what the sail foot may impart onto it, so there's that. Mounting the vang bail too close to the hinge can induce large bending moment in the boom, which is also why some mid-boom sheeting has blocks spaced apart along the boom underside rather than a multi-sheave block at one point. Lots to take into consideration there.
Oh, wonderful - looks like tinypic may be pulling a Photobucket. These may not open as large as I intended since I moved them to Imgur.
Re: Boom vang bail
Have you ever given any thought to the addition of a boomkicker......what effect it would have on the position of the vang.......I think suggested mounting location for the boomkicker is 30-45 degrees......say the boomkicker were mounted at 40 degrees would it be prudent to move the vang further out the boom since it would likely take more down force to overcome the boomkicker.