Your mother's home sewing machine won't cut it. Canvas work requires a heavy-duty machine.
Due to the acres of canvas on my boat, and the expense of keeping it in good repair, we invested in a commercial-grade sewing machine a couple of years ago. The first major project we did was to replace the enclosure over one winter's layup, and we saved at least $4K by doing so. So the first project paid for the machine 4-fold. And, we have the freedom of re-designing the enclosure or other canvas areas as we see fit, not to mention the upkeeping the canvas.
We have not only replaced the enclosure, but made a custom aft bimini, as well as many smaller projects. If your wife/girlfriend/significant other likes to sew, here is a chance to get her into boat project activities, as I am sure there is an almost endless number of jobs on the boat that will find their way under the sewing needle. But I find myself using the machine probably more than her. I figure, its not much differnt than a table saw, so it should be easy to get the hang of it.
If you are lucky enough to find a Singer "home" machine of the early '60s or earlier vintage, it might work well enough. Although these machines are long since manufactured, fortunately, aftermarket parts are available to keep them going.
If you want new, you have no choice but to look to an Asian import.
We purchased an Ultrafeed LSZ-1 Walking-Foot sewing machine from Sailrite in Churubusco, Indiana. The machine is of the Made-in-China variety (what isn't these days), but Sailrite modifies the pulleys, I think. At any rate, they fully support the machines they sell, have replacement parts, and can provide technical assistance for any mechanical problem you may have. You can even option out the machine so that you can hand-crank it, alleviating the need for electricity. I suppose this is more important for a sailboater, but they intend the machine to be kept on board. At any rate, I've successfully sewn through over a dozen layers of sunbrella (10 layers on this project), and anything short of a commercial machine won't be up to task.
While this is not necessarily a plug for Sailrite, its nice to find a company that stands behind their products. When I received the machine, the belt had a tendancy to slip off the hub. After contacting Sailrite, they sent me an alignment procedure within that very day so that I could get up and running. True, I could have returned the machine, but the expense for shipping (its a very heavy machine) and time to have it repaired meant my project would have slipped a couple weeks. Sailrite suggests that you try and keep the machine maintained yourself so that you can fix it years after the warranty expires, and they have created DVDs and owner's manuals that include repair and alignment procedures. This is unusual these days, especially for an imported machine.
While I bought the zig-zag version, the straight stitch version can be had for a few dollars less. I have to say, I have not used that feature much. But, if there is one thing I wish the machine had would be a larger bobbin, or another spool of thread that fit the lower shuttle, as it is annoying to have to constantly thread bobbins. When it comes time to do so, I usually thread several at a time, which at least reduces the annoyance somewhat.
If you use one of these machines, I'd suggest purchasing several spare parts. Number one on the list is a retaining cap spring, item 1603. They are about $7 each, and I'd buy several spares. When you are sewing through heavy material, or many layers of material, especially when you are still a novice, you will tend to pull on the material (or it might become jambed). The result of this is pulling the needle out of alignment, and that will cause the needle to hit the spring.
Repetitive strikes on the spring with the needle will either break the needle, and/or damage the spring. Once the spring becomes damaged enough, a burr will be formed on the edge of the spring, and it will tend to catch the thread. If your thread keeps tearing, especially the upper thread, check this spring. If the damage is not too bad, you might be able to file the burr. However, when this happened to me, the spring looked like it was hit with a jackhammer. I simply replaced the spring, and the problem was solved. So I keep a couple of spares in my sewing kit.
Incidentally, this happens on other machines as well. I was able to repair my mom's sewing machine that had the same problem by filing the burr off her machine's lower mechanism.
Another item I feel is essential is this Monster Wheel available as an accessory. It is a bit expensive, but if you are a sailboater and intend to do sail repairs out in the blue without access to power, this pretty much converts the machine to manual use.
Even if you don't intend to run the machine without electricity, it is very useful as there are times where you will want to run the machine by hand. For example, when we made our enclosure, we were adding Sunbrella facing to the front and back of an Ising glass window pane, which had a #10 plastic zipper in it (vent). A #10 zipper is pretty large, and we were able to sew right across the zipper - plastic teeth and all (under the facing), by using the machine manually.
I believe you could even sew sheet-metal with this machine manually!
So for those times that you want manual control, the Monster Wheel is a handy attachment. It permanently replaces the standard plastic wheel.
One other issue you will want to consider is whether or not to use UV rated thread. It is expensive, and not available in a lot of colors, but it will ensure the sewing is not going to rot or be damaged as quickly by the sun. Sunbrella itself is an acrylic, and pretty much impervious to anything, but the thread is not. I tend to use standard thread for anything but the most difficult things that I really don't want to re-do, as the UV thread is rather expensive. I have found that the V-92 size thread - which is normally the heaviest, works well with projects where you typically use Sunbrella.
The decision to purchase a sewing machine is probably going to be determined by the cost of repairs, vs. the cost of doing it yourself, coupled with your skill level. But if you ever obtain an estimate of replacing your enclosure, I think you'll seriously consider purchasing a machine and doing it yourself.
One last thing on this topic. Building a new enclosure yourself may save you $2K to $4K or more, but it is labor intensive. If I were doing this for someone else, I'd sure be charging what canvas shops charge, as it is a lot of work.