As a marine canvas fabricator who started out doing canvas on a cruising sailboat using an LSZ-1 I thought I would throw my two cents in as well.
When I first started doing canvas work using the Sailrite machine I thought that the zig-zag was an absolute necessity for the heavy-duty sewing of marine canvas due to strength of the stitch.
After having returned to life ashore a few years ago I went to work in a sail loft doing custom canvas work and I recently opened my own custom canvas shop here in Annapolis. During my time working in a sail service loft (all repairs
, no new sails) I can tell you that for most sail repairs
on cruising sails the zig-zag stitch is not necessary.
The zig-zag stitch and the three- or four-step zig-zag that a lot of the industrial machines are capable of is necessary in sail-making more for the even stretch of the sail than for the strength of the seam. Most cruising sail repairs
that are done by a sailrite machine are not precision jobs and don't need to be. Especially if your boat is longer than about 35' I would imagine that you'll need to get it to a loft occasionally to take care of the bigger jobs which means that the Sailrite repairs
are more of a temporary fix.
Anyway, to sum up, the zig-zag stitch isn't necessary for 99% of the DIY repairs out there but a lot of people think that it looks nice and nautical in which case sure, go for it. Is it worth the $150 extra? I would say only if you plan on doing a lot of spinnaker
(or gennaker, screacher, code-zero, etc.) repairs which rely more on the even stretch of the stitching than a big heavy cruising main or genoa does.
Just my two cents.