The wetted surface on a Tonic 23 is small enough that two and a half litres does the hull with paint left over for the keel.
Knowing what is already there
Boats this age have been painted by five owners with whatever was on the shelf. A test patch tells you in a day whether the new paint lifts the old.
Preparation
Wash, scrape the loose edges back to something sound, and feather them. Sanding the whole hull every year buys nothing and eventually takes you into the gelcoat.
The waterline
Tape the line with the boat level on its trailer, not on the hard where it sits bow-up. A line taped on a tilted hull looks wrong the moment the boat floats.
The keel
Iron needs a primer the hull does not. Treat the keel as a separate job with its own build-up, and it will stop staining the boot top every summer.
