Thanks guys, all good info.

I'm planning on two total, [one each side] given that currently I can hold the sheet without any ratchets. It's not comfortable, paticularly if it's blowing over 12/15k and the reach is a bit long but I can do it so I think one a side should be enough. Also, the spi is only 100sq ft.

I looked at the Holt's and the price was definitely attractive but they don't quite look 'the goods' to me. I wonder if they warrant them? Maybe they could handle the loads of a 14ftr spi? Money is tight with me presently and definitely a consideration.
In any event, thanks for the advice, I'll let you know how it turns out.
Bern.