How to control mainsail twist ?

I’m building a second boat for a class where no commercial items are available (RG-65, popular in south America and Europe).

On my first boat I experience a lot of twist on the mainsail (a high roach, low aspect sail). The sail I made myself, using spinnaker cloth (0.75 Oz). That particular sail have no leech line.

It twists a lot (almost 90 degrees relative to the boom).

Do I have to attach a leech line to control/prevent twist on top of the sail? If so, what is the easiest way of doing it?


Will making the upper most battens in the sail go completely to the luff and punching the hole to attach it to the mast thru the batten help?

BTW the mast have moderate bent as the mainsail have a straight luff. No sagging on the sail neither.

Any ideas?

big stiff battens in the head of the sail help. taking up on the outhaul of the sail will flatten it to a certain degree also.

Curious to know where your boom vang is at?


The vang is attached at ~45% of boom lenght from the mast. Now that you mention it, the thing I made for a vang is not very tight, not loose either… but it does allow for a 2-4 mm raise at the boom end…

Hmmm think I’m answering my own question here…

Yes - you are answering you own question. There are three controls over twist - the boom vang, the mainsheet (not really used as a twist control on RC boats, except when hard on the wind), and the shape of the mainsail itself.

Firstly, try controlling the twist with the vang. If you still do not get the desired results, we need to look at the shape of mainsail itself. Did you make it with panels?

The sail wasmade with a single panel. Will try to induce some shape into it with seams accross the luff… thanks all!