Hi Thomas, It is on the borderline for working as a sailing model. There is a lot of sail for a small displacement.
You can gain displacement without compromising the waterline by.
1 additional layer of planking, say 3mm or 1/8th inch. on the underwater section faired up to the main hull.
2 Make the keel thicker by almost double its width. The side view of the model stays true. The underwater part is not obvious.
Doing the above will give about 20 - 25% more displacement. This will give you the extra displacement to carry enough lead in the keel.
I suspect if it were easy to convert we should be seeing more of them on the water.
Most of all build as light as possible and use lightweight RC.
You might find that a cheap and light option for sail winch is to buy a 5kgm pull standard size servo from Howes of Oxford.
The mast weight will have a big effect on stability, you might like to try an aluminium groovy mast.
However you may find that she is only suitable for light breezes.
I have converted a larger static model than this to work and did all of the above but had to fit an extra keel. I think you may not have to do this as you are building to 1:10 or 12 scale and I was building to 1 : 35, so the scale effect is with you..
Good luck, Roy