How do you check to see if a boat is fiberglass or carbon fiber?

Carbon has a dark grey to black look, Kevlar is yellowish and glass is a light grey to whitish ?

Carbon will conduct electricity, fiberglass will not

Is there anyway to tell if it has gel coat on it

Your best bet would be get some good pictures and post, you will need 10 posts prior to being allowed to upload pictures

Tap the hull side laminate.. Carbon will have a slighter lighter tone than a standard fiberglass laminate since it will not be as thick and a little stiffer. Look inside the hull where you can see some unpainted laminate/tabbing. Carbon will show through layers of fiberglass on top of it. I used 100% carbon with Nidacore in my T-top hardtop to save weight w/o sacrificing strength. The underside is clear and the carbon is visible. I did not use carbon in the hull of my 28' center console as it's properties would not add that much extra strength and stiffness to a hull that was already very strong. Carbon has it's uses but a pleasure boat hull is overkill in carbon. Maybe a race boat hull but the extra material cost is substantial.

OP what do you have that you think might be carbon