Boom Vang

[Daveinet]

My current sailboat does not have a boom vang. The main sheet attaches to the middle of the sail, which means there is nothing holding the end boom down. I had rigged up a temporary vang when I used an alternate boom and sail, but now I would like a more permanent setup.

All boom vangs seem to be made up of a block and tackle setup. While this idea seems to be fine, can anyone thing of a reason I would not want to design it with a solid pole vang, with a turn buckle? Part of the reason I was thinking this is that when dropping the sail, the boom drops. it just seemed to me, that a solid vang could serve 2 purposes, both in holding up the boom, as well as holding it down.

[sailingdog]

Your mainsheet is probably attached to the middle of the BOOM, not the sail. A boom vang is generally not attached at the end of the boom, but about a third of the way back from the gooseneck. The end of the boom doesn't need to be held down if the boom is held down further forward, since it doesn't really bend. The purpose of a boom vang is to help keep the boom from rising when the boat is sailing on a beam reach or deeper. When sailing a close reach or close hauled, the mainsheet acts to keep the boom down, so a vang isn't really necessary for those points of sail. As the mainsheet is eased, it has less ability to affect the boom's height, and the boom vang becomes a useful tool.

The reason boom vangs are made up of a block-and-tackle setup is to give you decent leverage while allowing the boom vang to be adjusted quickly. A turnbuckle and solid rod would not have the adjustment range or speed of adjustment to be usable safely. It would also not be adjustable from the cockpit. There are solid vangs, but most incorporate a block-and-tackle of some sort into them.

It would help if you said what boat you're considering putting a boom vang on, since that would help people figure out what size boom vang you need. Garhauer makes both rigid and soft boom vangs that are reasonably priced.

[Daveinet]

I assume most are not going to know what a AFC mini toner is, so here is a photo.

And yes, I meant middle of the boom, not the middle of the sail. Small boat, so I should be able to reach it from the cockpit. I assumed fairly coarse threads to make the adjustment easy to change quickly. I've actually got a reciprocating ball screw laying around, they can also be purchased surplus pretty cheap. (currently motor driven, but that is probably overkill)

[Faster]

There are a variety of rigid vangs on the market, but honestly that would be overkill for a boat this size. Your 'turnbuckle' strut idea would be impossible to easily adjust as often or as far as it's likely to be required as you change points of sail and wind strengths. In extreme conditions a vang needs to be instantly and completely releasable to avoid damaging the boom.

Rather than reinvent the wheel, stick to what's worked for decades and use a nice compact block and tackle arrangement with the proper attachment points.

[JohnRPollard]

Originally Posted by Faster

There are a variety of rigid vangs on the market, but honestly that would be overkill for a boat this size. Your 'turnbuckle' strut idea would be impossible to easily adjust as often or as far as it's likely to be required as you change points of sail and wind strengths. In extreme conditions a vang needs to be instantly and completely releasable to avoid damaging the boom.

Rather than reinvent the wheel, stick to what's worked for decades and use a nice compact block and tackle arrangement with the proper attachment points.

Dave, this is solid advice that Faster offers. Just keep it simple and use the block and tackle arrangement that serves so many so well, especially on smaller boats like yours.

But in case you need more convincing, another problem with fitting a rigid vang is that it can place a very high load at the pressure point on the boom where it attaches. You would need to reinforce the boom in that location in order to prevent it from bending around the vang strut, or even snapping the boom clean. This can be done (usually by fitting a bracket that spreads the load) but again, it's overkill for your boat.

the other nice thing about going with a standard block/tackle boom vang, is that it can also serve as a preventer and as part of an MOB recovery system. On small boats with limited space, it's nice to have hardware that can serve more than one purpose.

P.S. Nice boat. Looks like a lot of fun.

[Nacra52]

I remember a pole type boom vang becoming a projectile on a boat I was sailing on. It was destroyed in the process and we completed the voyage without it, and at least I didn't notice a big difference.

Perhaps as a result of this experience I don't really like pole type boom vangs and would probably never use one, even if the boat came so equiped.

I don't suppose the mini-tonner would generate enough force to snap one and turn it into a deadly missle unless you used 1/4" dowel rod or something for it.

[nickmerc]

The ballscrew idea is not great since it can be easily backdriven. Most likely the motor that is attached to it has a brake on it or a gearbox.

Since you are also concerned about holding the boom up when dropping the sail as well as pulling it down when reaching, you can use a topping lift and boom vang combination. It is very affordable since it is only a few blocks and some line.
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