Easiest way to reef main with hand-sewing is like you say - a series of loops of line hanging from sail, ready to be tied around boom, when halyard is dropped a bit. Beware of stresses on the sail, however.
Monohulls have variations of this where a line is pre-arranged through blocks on boom and through eyes (grommets?) on sail, so pulling one end of line results in reefing entire sail - called "jiffy-reefing, I believe. Here's an illustration of a dinghy reefing system. Notice the reinforcements at leech, luff & some of the grommets.
http://www.imagic.demon.co.uk/openboat/yerbury.htmlI guess this could be adapted to a catamaran sail.
I think you should consider getting over your fear of turtling, through a series of improvements.
1. Seal the mast - make sure there are no way water will get into mast when it lays on the water. Even add flotation at top to prevent it fromgoing under, if you think it's needed.
2. Don't tip over - Usually new sailors tip over for two reasons - they don't know they should be unsheeting before it's too late, or when they try to unsheet, it doesn't go quick enough. Make sure your mainsheet cleat angle is easy to uncleat from whatever position your sailing, and that the mainsheet runs *out* through the blocks easily.
3. Learn how to right the boat. On day with low wind, near beach, with help nearby, intentionally turn it over, and learn what things make it easy or hard to right it. Then when you *need* to right it, you'll have the experience and confidence to do it.
4. Don't tip over - become better sailor, able to anticipate gusts and read the wind - e.g gusts on the water - are they headers or lifts? - is the oncoming gust more likely to suddenly push you up & over (change course upwind or release sheet a bit), or will the gust just temporarily increase your speed without overpowering you?
Remember, those of us with boats that have more powerful sailplans may be impressed with your ability to find enough power in your sailplan to turn your boat over!
Another thought - does your boat have a traveler? If not, you might consider one.
