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A Catalina 34 (I have one, too) does not need to be measured. They made 1800 of them. If a sailmaker doesn't have those dimenions, for a mainsail, I'd pick another sail maker.
Go local as noted. Or use sbo or CY's Ullman loft.
Good luck.
You're not the first to ask this, right?
New sails Experiences/Recommendations
c34.org
Ummm, Stu, I disagree. The rig should be measured for every new sail, even if it’s for the most popular at ever built. I owned an online loft for many years, and we never built a single sail without detailed measurements. If the owner wouldn’t do the measurements and take pictures, we turned the business down.
Why? Over time, owners make changes to the boom, gooseneck tack pin, reefing gear on boom,, outhaul, sail gate, for mainsails. For headsails, they change furlers, track positions, mast rake and more.
The owners did the measurements according to our detailed instructions. We also required photos of everything. Most good online lofts do that. If they don’t, there’s a risk there will be wrinkles at the tack, reefing won’t come down to the gooseneck, etc.
We also required measurement that told us how the rig was tuned, for example: mast rake, static and dynamic mast bend, estimated forestay sag). If the rig was tuned oddly, we talked to the owner and instructed them on how to tune it properly.
Judy B
Retired Sailmaker/Online loft owner