I rubbed them all back, treated them with vactan, put on primer which dried really fast in the warm sun and the breeze and got on a dab of primer /undercoat too. Next week if the weather holds I'll put on some more layers before repainting the whole roof with a fresh top coat.
Actually I was was quite encouraged. When you rub these rust spots back, they are tiny. In some cases I think it must be a fragment of metal dust or swarf in the paint because there is fresh paint beneath the rust spot. Anyway the roof now looks like this. The undercoat is a darker grey than the top coat. With a fresh top coat we'll be as good as new again.
Meanwhile Glenda was popping round looking at strap positions for the cratch cover and still offering me choices of this and that regarding the design. It was too breezy for her to mark out her paper template in situ, so she was getting on with making straps etc. She was also preoccupied with the missing man.
Moored the other side of me was a boat for which Glenda had just finished the cratch cover. A bit different from how ours will look but here it is. Ours will have bigger windows and I think wider "doors". One of the main features we are seeking is a shorter "tail" pressed studded out of the way of marauding lock gates.
She was regailing me with tales of how asymmetrical some boats are. Cratch boards not central, one side of the boat an inch higher than the other etc. I suppose that's because they're hand built. It doesn't make her job any easier.