contrary to some of the other replies, and depending on the machine, I highly recommend a GOOD home sewing machine for most projects concerning boat canvas and upholstery.... especially for someone who is just starting out
I will add, that a heavier machine is always better, but it is almost always a lot more money and most of us will never run our machines at a high duty cycle, even though we may have a heavy duty job once in a while.
a well chosen "home" model will do almost everything you will ever need to do unless you are sewing heavy harness leather or thick rubber, but it just wont do it as fast.
about 30 years ago, I had a basic singer machine that was a bit light for what i needed and i finally got another old used machine that has been going strong since then.
its an old husqvarna/viking 21-A 2 speed, that will easily punch thru up to 9 layers of sunbrella (its difficult to fit any more than that under the foot)... and sometimes it takes some patience to get the wad of material thru the arm, but a little pre-planning and it all works out just fine.
I have been using it for years and without any problems....
when using a home machine, the limitations are the size of thread, the length of arm and the power to push thru multi layers of heavy material.... choose the machine that covers what you want and use it...
if you need a machine that has a long arm, can take large thread and has a lot of power, and will be used a LOT over the next few years at a high duty cycle, then you need a good quality industrial machine... but if you are only going to be doing a couple of upholstery jobs, a few sail/jib bags, biminis/dodgers and a few other projects the next few years, a well chosen home machine will get you by just fine. they last a long time if maintained properly.
a machine with a walking foot is the second most most desirable feature after power...
ive sewn sail cloth which is very easy material to work with (making bags), but I have never sewn sails, so i wont make any recommendations here about that.
if money is no object for you, buy bigger and better.... because that is exactly what i would do if i thought i needed bigger, but with some of the creations i've made over the years with what i have, i cant see the reasoning for needing a bigger machine.... but others who have not been so lucky to have found a good strong "home" sewing machine have purchased the heavier industrial type machines and are completely happy...(why wouldnt they be

)
but dont rule out the more affordable option just because the first light duty/entry level model someone gives you, doesnt do it for you.... look for a good strong one.