Just a point of clarification, not meaning to be pedantic - loose-footed means that a sail is only attached to a boom at the clew and tack (2 bottom corners) instead of being attached along the entire length of the foot (bottom edge). Not having a boom at all is simply "boomless".

You say that you built the Mark III SailRig, but not which sail you're using. Since it's for a WD12, I'm assuming the SailRig 40. Or are you using a different sail than the CLC SailRig sails? If it is the 40, you can use the same boom that the Eastport Pram with its 42 sq ft sail uses. From the line drawings and photos that looks to be 1-1/2" so a piece of clear DIY hardware store 2x2 pine should work. Alternatively, for a better result you could laminate a pair of 1x2 boards (actual dimensions 3/4" x 1-1/2") to make a 2x2 that would be more resistant to warping.

And if it was me, I'd skip the goosneck, drill a hole in the end of the boom and lash it to the mast. Much cheaper than a gooseneck and more durable, too.

Finally, keep in mind that you may have to make the rig loose-footed, depending on the shape of the sail. Or, it may just not work at all. That's another reason to go with a lashed boom from the DIY store. If it turns out to be a bad idea you won't have that much money sunk into it.

Laszlo

   Sorry, Laszlo, you're right about my mistaken terminology. My sail is the 70 sq. ft.  sail that John refers to in his article about the SailRig as the Mark III version.  It's a very powerful sail , but loses it's shape when running downwind, even with its full-length battens. My suspicion is that it would require more than a 1x2 for a boom.  I was hoping that someone had already figured out what is required, and save me the R & D.

   Sorry again (it's early and my coffee hasn't kicked in yet).  I meant 2x2. I wouldn't mind it being loose-footed, as long as the sail is connected to the boom at tack and clew. 

For a 70 sq ft sail you could use the same boom size as the PassageMaker or Peapod, whatever those are. If no other builder pops in, call CLC.

Laszlo

My skerry with the lug rig has a similar size, but dissimilar shape to the MIII sail rig.

It uses 1.5x1.5 with tapering on each end.

given the sail rig dimensions shown I would think that you are putting not as much stress on it.

I have also thought about a gooseneck but as Laszlo states lashing it to the mast works just as well for less.

   Thanks, everyone. I think I'll go with a laminated stick of about 1-3/4" square, rounded off, and laminate some jaws for the forward end from left-over scraps of marine ply (I have lots of those).  Drill some appropriate holes for the downhaul and tack, and the same at the back for an outhaul.   Should work.