I always hear people mixing these two up as they tend to have the same function in most people’s minds. There is, however, a difference between the two. Although both pictures are from the Harken website, the goal isn’t to promote their products. I just think they make high-quality products and had some good pictures to show the differences.
Why do These Exist?
The main reason we have these on boats, as explained here, is to allow to flatten out the main sail. This is done by tightening up on the vang or kicker.
The Kicker
I call this one the ancestor of the vang. It was the way used for the longest time and is still used to either cut costs or on smaller boats. The goal of this particular one is to give you a 4 to 1 advantage on your strength to be able to pull down the boom.
One of the big advantages of a setup like this one is being able to use a winch without any worries of breaking something. As long as it is properly riveted into the boom and mast, you shouldn’t have any worries.
The Vang
This is a vang. Trust me, you won’t see this on a Laser I anytime soon. Not only does it sell for the price of a Laser, the weight of these just makes no sense. When it comes to yachts though, it is what you need.
The way it works, if it isn’t hydraulic, is it is made up of two metal tubes with a spring in the middle. You still get to tighten it and pull down the boom but you also get the spring that will easily hold up the boom.
When you need to remove the topping lift, which normally holds up the boom, you don’t need to worry about the boom crashing down into the cockpit as the vang will support it.
The downside to it is that to avoid damaging the spring on the inside, you should never tighten it on the winch. This means you might have to put more strength into it to get the sail shape you want.
Now that you know the difference, I hope you can see why we have two names for things with the same function. Many professional skippers I’ve met don’t know the difference so you’re already one step ahead of them!