I am a huge proponent of using the all metal domestic sewing machines from the 50's, 60's, and early 70's. Some of my favorites are Kenmores, Singers, Brothers, Pfaaff (as previous poster mentioned) or just about any of the all metal machines from Japan made during that era. I contributed a lengthy post on this site, about choosing a domestic sewing machine.
I just got done sewing a sail cover for my Catalina 28 using my 1968 Kenmore. It came out very nice.
That said, for what you describe, a domestic machine, no matter how robust is not going to serve for what you intend. For one thing, you'll have a hard or impossible time using anything heavier than V69 thread, and you definitely want to be able to use heavier thread for what you describe. Also, you really should have a walking foot machine. Yeah, I was able to do my sail cover on the Kenmore, and I'm also able to do hatch covers and so on, but there quickly comes a point where you need a walking foot machine to feed multiple layers of tough fabric.
The minimum would be the Sailrite Ultrafeed zig-zag machine. It has only a slightly larger motor than the vintage domestics, but is also geared down more to punch through heavy fabrics, albeit at a slower speed. And it has a walking foot. And, it takes heavier needles. There are other sewing machines similar to the Sailrite, at about half the price, but they aren't nearly as good as
the Sailrite.
The Sailrite machine is diminutive, which is good on a sailboat. If you find that you want to do a lot of work on sails, it's small size will be a problem, as you'll be unable to feed the rolled up portion of the sail through the machine.
The next step up over a Sailrite is going to be any number of true commercial or industrial machines. I really liked my Consew 206 rbi, but I wouldn't/couldn't have it on a sailboat. The motor is the size of a toaster and mounted underneath a heavy duty table. That's pretty much going to be the case with any industrial machine.
As sailors, we're lucky that Sailrite exists, as IMHO, there really isn't a similar, competitive product. Plus they have excellent customer service. Visit their site and check out all their how-to videos if you haven't already.
IMHO, there is no similar or competitive machine to the Sailrites.