Boom Vang Rule of Thumb

[Bluenose]

I am having an old Shield One Design sailboat modified to create a modern Knockabout type sloop and I am looking for a way to maintain a boom vang. The current Shields boom vang is quite shallow at about 18 degrees, plus or minus depending on the source, as measured from the boom horizontal.

You can see the shallow angle while sailing in this picture.



And here is class sail plan.



Here is my concept with the cuddy cabin. Obviously I have reduced the space for the vang (please ignore my vang mockup since it is just a place holder right now).



I have research various other class boats and some have quite shallow vang angle. My question is, is there a limit to this or a rule of thumb. Or better a set of design guidelines concerning minimum angle, distance from the mast etc. Any help would be greatly appreciated.

Bill
Lopez Island, WA

[Ian McColgin]

You don't need the vang on the wind. Why not do the work you'd have with running backs and have a vang to the rail for each side, let the lazy side just lay across your cuddy. Maybe couple with the so called "boom brake" so it's nearly self-tending if you're tacking down wind.

G'luck

[kristian]

KInda like the twin vang idea, I think then they're techinically twin preventers. Udells and 22sqm use that setup.

Upwind and close reaching, the leech tension is all done with the mainsheet on a Shields. When racing we actually find it lots faster to leave the vang slack until downwind.

You could always put a curved traveler track on the cabintop to run the vang too, like a Star.

Honestly I think the least intrusive situation would be to install a standard 8:1 vang with the bail as low as possible. It would probably work well enough for anything but a long reach, in which case you could rig a removable preventer tackle.

[Bluenose]

You could always put a curved traveler track on the cabintop to run the vang too, like a Star.

Kristian you don't know how many layout I drew trying to get a curved traveler track on top of the coach roof. I ran into a bunch of problems. The first was that the coach roof has curvature so the traveler track would have needed standoff towards the sides and I couldn't find a way to transition at the front. And then even using the Star curved track, which I believe is the smallest Harken sells, I didn't have enough width on the cabin top. And then there was making the cabin top strong enough to support the loads. So that is why I am where I am now.

I think I will try your idea about putting it in at whatever angle I can get (did I mention that I would also like a rigid vang) and sail it for a bit. I will also think about the two vang option if I end up not liking the current setup.

So you are in the paint shop? You just had to get there before me didn't you? I can't wait to see the results. By the way, does Shields 88 have a name?

Cheers, Bill