We couldn't afford the sailrite
machine, so looked around and bought a Janome HD. Very basic all mechanical with steel
drive train and aluminum
body. It has no problems with 5 layers of sunbrella and a plastic window at the same time. Used it to see new cushions
throughout the boat
as well. This involved in sewing through 4 layers of marine
vinyl which it also did with ease.
YouTube has videos of people sewing through wood
yardsticks with these things.
Look for a heavy duty machine with no electonic gizmos. Most can handle thicker cloth and even some sail work
with care. Old thrift store units can be good, but note a good older machine will likely be very heavy due to the solid steel