Sorry if I'm using incorrect terminology. Can anyone tell a landlubber the proper technique to lash the mainsail to the boom and gaff. I'm using tarp sail with half inch grommets to a windsurfing boom. The manual looks like a continuous length of 1/4" line was used. But I'm not sure how to make the knot at each grommet...
You can just tie the line off at one end and coil it through the grommets. Some use a half hitch at the grommets and some use other non-traditional methods like a cable tie through each grommet.
Paul will probably check in with the correct nomenclature.
I concur. If you do it right it gives you that barber pole effect.
Thanks much. I did the half hitch on the Gaff.  Don't have the boom done yet but I got all the lines run and untangled today. I have to get the HIN on and get it registered. Kind of hoping for a Labor Day launch. Not as well finished a boat as I've seen most builders do on this site but hopefully just as fun. Will post some pics when I know it floats.
-Mark
There are a few different ways to lash a sail foot to a boom, though it should be noted, the sail should be shaped with a "shelf" in the lower portion, if you want it to set well. If making a poly tarp sail, this means some thought about the foot, probably a dart or two.
On daysailors, I prefer loose footed sails, especially if home made, as they're much easier to shape, both while making them and sailing them.
If going the lashing route, I use an "up and back" technique, which is a lot harder to describe then to show. Of course I don't have a picture handy, so here goes. Instead of spiraling around and knotting each crinkle (grommet), I go up one side of the boom or gaff, looping through every other crinkle, then come down the other side, looping through the ones I skipped. This lets the sail side on the boom easily, so tension on an outhaul is effective. I don't knot at each crinkle, preferring the sail to take a natural set as it flops from side to side. Knots tend to lock the sail down, limiting this action.