Thanks kgg and dikman
I will investigate servos, hopefully available locally. The ones from China work out double the cost with freight to here.
I didn't realise my thread needed such a large needle so I'll look for some #22 needles. Thanks for the thread chart - it explains a lot.
What brands of thread do you recommend? I just got some random stuff from AliExpress to start with and they are labelled SanBest.
Sorry I know nothing about canvas weights yet. I don't want to experiment on expensive fabric such as Sunbrella, so will try and get something locally to run some tests on. When I look on AliExpress there is a huge range but I have nothing to compare them to. They mention things like Oxford, Polyester, 200d, 300d, 600d etc up to over 1000d but I believe those higher weight ones are PVC which I probably don't want. I have one very heavy custom PVC cover which came with the boat but it didn't last long. The other covers that came with the boat are some kind of canvas but I have no idea. I will start by making a winter cover for over the whole boat, with a bottom drawstring, a couple of tie downs, maybe vents, maybe an access zip. I have a couple of existing covers to model it on. Depending on roll width I'll need about 30m just for that, but may as well buy more to make some of the other things.
Alternatively, I could just buy a smaller qty to see if it is any good and make a BBQ cover.
Some pics if anyone is interested. The black thread is the top, the white is the bobbin thread and looks tight as you can see. The material is about 6 layers of old rags - cotton bedsheet.