I left the primer to harden for a few days and then started to sand it flat, using a P180 grit to remove brush marks followed by a P220 grit to polish it smooth.
This went well and I sanded most of the port side before my trusty Festool Rotex 90 abruptly stopped working.
It did this once before a few years ago and it turned out that the brushes had worn out. I suspect that this has happened again.
No choice but to put it in for repair. Luckily there is a Festool dealership in Eynsham, so off it went the following day.
I wasn't too worried because I had the DeWalt palm sander which worked well when I sanded inside the cabin, so I set it up with the vacuum cleaner and carried out a test on the starboard cockpit deck.
Like this.
Unfortunately it was not successful, and sanded through the primer to bare substrate, so that won't work.
The problem is that it is too aggressive. I use a soft interface pad with the Festool, which eliminates this problem.
So it looks like I will have to wait for my go-to sander to come back!