What to mark props with for testing

[jester_s1]

I read you can mark props with dye and then run them to see where the water is being pushed at the back vs. the tongue slowing the boat down from pressure on the front. What works for marking it?

[TheShaughnessy]

https://www.overtons.com/modperl/product/details.cgi?pdesc=Birchwood-Casey-Presto-Gun-Blue-Pen&i=200264&CAWELAID=120030620000090559&s_kwcid=adwords__&gclid=CjwKCAjw7cDaBRBtEiwAsxprXX15s_ADLlWZjx6nZVdmLeR0YZvOVjHhyGVYkPq_Ca6a5173KPnhmxoC-d4QAvD_BwE

I've only ever tried with a regular sharpie but I have read you can use a blueing pen

[jester_s1]

When I had a catamaran I tried with a sharpie, but two runs didn't remove any of it. So at least for that boat, the sharpie stayed on too well. Maybe one of my daughter's Crayola non-washable markers will work. I don't really want to bother with buying a Dyekem blue pen if I can get away with something I already have.

[kfxguy]

Is this really a thing?

[HTVboats]

I have seen Marty Davis (a true prop Guru) use some sort of tooling dye on props to see where the high pressure areas are. I believe the dye wearing off shows the pattern. As for sharpies I use them to identify props and mark some with pitch and diameter when I cut them. The Sharpie stays on the blades and barely wears at all. On full size aluminum props you can see cavitation burn on the paint and exposed metal.
Mic