Is polyester gel coat catalyst the same as the polyester resin catalyst?

Yes.
MEKP
methyl ethyl ketone peroxide.

The only other thing is for those that don't know, There is a clear and and a red. The red has just been dyed that way so you can see when you have it mixed and so you can also tell if a mix has been kicked before you start laminating. Very important.

Obviously you would only use the clear for gelcoat.

I just redid my hull centrelines with flowcoat (by brush) after grinding out soft spots and reglassing in what is the first bottom job in years. I could feel the flowcoat becoming harder to apply but it was still tacky 24 hours after application. Any reason for that? Temperatures were from 16 to 24C.

Was that gelcoat? If so, either humidity got to it or it wasn't sealed off from the air for cure.

Remember for polyester: Dissolved wax keeps the sticky away from finish gel-coat. Bonding polyester resin has no wax. Methyl ethyl ketone (or 2-butanone, a cousin of acetone but with one more carbon atom) is the solvent plus a little benzoyl peroxide makes the catalyst.

I'm not familiar with flowcoat. But I'm assuming it's some kind of polyester gelcoat. Gelcoat stays tacky in presence of air. You have to make an air tight cover to let your gelcoat cure completely.

There is a number of ways to do this:

- Mix some wax in the gelcoat before application. The wax is pushed to the surface as the gelcoat cures, it makes a air tight cover, done.

- Wrap it up. Get plastic sheeting that doesn't react with polyester. I think polypropylene should work. wrap your repair, tape the sides, done.

- Use PVA glue. Dilute it with water and spray or brush over your repair. It's going to form a film once dried which is going to let your gel-coat cure.

I'd say go with solution 3. PVA glue is cheap, could be found anywhere and is easy to apply. And smell good as well

I re read the label on the can to find flowcoat is waxed. Lesson learned, apply during daylight to ensure a speedy cure.

The flowcoat is rock hard...as are my cat's footprints along the keel! More sanding.