I've been using the Ronstan Smartratchets. I find I can hold the spinnaker sheet in one hand with one of these on the sheet. If I'm getting tired I might put a wrap around my hand but usually I just hold it.

I know Gary found that one wasn't enough for his F16 Altered, and he put two Smartratchets on each side. The loads are that much bigger. I would guess an F18 would load up that much more again.

I should mention that all the Mozzies I've seen have this kind of setup to increase the wrap around the ratchet block. Maybe this wouldn't be needed with the harken blocks.