Hi People.
A friend of mine has a brand new secondhand yacht (40ft) and we found this fella down below. I suspect it is required for raising/lowering the mast but if anyone knows better, please educate away....maybe its a vang??
Select to expand quoteh28kurt said..
It's a Walder Boom Brake designed to slow the main down though Jibes
It sure is. I think you should rig it. Check out the Youtube videos and report back. I made one on the lathe but was not particularly taken with it's performance.
They are worth a few bucks!
I have a walder boom brake (similar to shown - but not exact) and swear by it. Indeed, as a risk management tool against, hard crash jibes, head injuries etc. this is cheap insurance at around $500. Many folk prefer restrictors, but my view is they are harder to set up/manage/control.
With a 50m2 main , I have mine set up around mid boom, with line back to a 4:1 block next to the helm.
It takes a bit of practice to work out the right tension (based on friction through the screw type pully), but as in my case, I can use it like a handbrake and make fine adjustments depending on wind strength.
Result - no more unexpected jibes & very controllable mainsail movement either tacking (softer) or jibing.
More importantly, my wife and kids love it! 
