You were on the right track to heave-to except,if I read your description right, you left out one important step. Once you have the right sail combination to be properly balanced when hove-to (you have to experiment to get this) you have to tack but without casting off the jibsheet
. This means that the jib stays on the windward side trying to blow you away from the wind while the main is trying to push up into the wind. You adjust the tiller to get the balance exactly right. When you get it setup right it will be very comfy and much better than bare poles (all sail down)
Things to think of:
- decide which way you want to point after heaving-to (to give yourself more sea room or to take waves on the favorable side) and then start on the opposite tack before the maneuver
- you can't just go below and wait for morning or nicer weather; there may still be traffic out there so you can to keep watch from time-to-time - how often depends on visibility and potential traffic. For what is worth, if you heave-to on starboard you will right-of-way over other sail boats, but I would not trust that they will see you
- heaving to is not too hard on the sails since they should both be filled and not flogging
- you will not be stopped when hove-to but will be forereaching at 1 to 3 knots or so.
As to angle of vanishing stability, I think this is calculated empirically when boats are rated for racing with some of the fancier rating rules (IMS?). I suspect that a Grampian 30 has not been measured like this. If you go to the Sailcalc website you can see a number of measures for your boat and a couple of thousand others. One of these is capsize ratio which is a something similar to angle of vanishing stability (although it is not an angle). The capsize ratio for a G30 is 1.85 with a lower number being better and any value less than 2 being fairly good. The website is Sail Calculator Pro v3.53 - 2000+ boats