Boomvang on a Mac 25

[Bruce Trotter]

I understand the Mac 25 did not come out with a boom vang ( mine does not have one) and I was told it would be a good idea to put one on it. Since the distance from the base of the mast to the boom is rather short does any one have a formula on how far out on the boom it should be attached? I have ask several boat owners and seem to never get the same answer( no Mac owners). I have a hole in the boom at about 46 inches from the mast but that seems to far considering the angle it would put on the boom vang. One catalina 22 owner said they should be at 37 inches. Anybody that has a boom vang , where did you put yours? Any Comments ?

 

[Doug Rodrigues]

Equal distance from the goose neck.

Attach both ends of the vang pully system to be exactly the same distance from the goose neck. That will be the angle resulting in maximum pulling force on the boom. It's debatable if moving the boom connection further away from the mast will increase the pulling force. I believe that doing so only changes the fulcrum point and cancels-out any leverage advantage.

 

[arty]

depends on length

You can locate your vang the way Doug suggests. The Catalina owner? He must be smoking something funny. But remember, the shorter the hypotenuse you establish, the higher the pressure that will be exerted on the tackle and the stronger it needs to be. It you have 24 inches deck to goosneck, and your boom is 8' long, a vang set at 24" out on the boom will give the mainsail a 4:1 mechanical advantage (8' to 2'). At that length, your vang attachment points will need to be TOUGH and you'll want to rig up at least an 8:1 mechanical advantage on your tackle - otherwise, your wife will never be able to trim it under pressure - and that's when you need it most.

 

[Doug Rodrigues]

Mathematicians out there ??

Anybody out there good with math calculations? I would be curious about angle of force; stress on the boom at what distance from the goose neck, etc. Does anyone know what the boom vang manufactures recommend?

 

[billy w]

boom vang

No matter where you attach the boom vang to the boom, the fulcrum point will be the same and that is where the boom attaches to the mast. The boom in relation to the vang can only go up or down no matter where the attachment is made. It can not move horizontally since it is stationary at thr mast fulcrum point. My advice -- attach the boom vang to the boom at the existing hole and to the BOTTOM of the mast. The boom should be short enough and stiff enough not to have horizontal bend under tension from the vang at that distance. The boom is the fulcrum lever, the gooseneck is the fulcrum point, the sail is the load, and the vang is the power. Be sure you don't have too much power.

 

[George B.]

Boom Vang

The purpose of the boom vang is to keep the back of the boom from rising, so logic would dictate that you want it as far back on the boom as possible. Placement is also going to depend on other equipment such as mid boom sheeting and whether it interferes with going up or down the companionway. Vangs with angles less than 45 degrees are going to duplicate the down haul's force as much they are going to keep the boom end down. Three feet back is about right for a Catalina 22. More importantly is how you mount it. Use an eye strap on both boom and mast to distribute the loads and tap for machine screws. A vang will pull sheet metal screws right out. Also, you may want to consider snap shackles on both fiddle blocks. It will make it easier to rig and de-rig, and you can reposition the mast end to a piece of T-Track or a deck eye pad and use it as a "vang-preventor"