1993 2.5 (200hp) mercury outboard motor put boat in water started motor motor was knocking, quit knocking why

Question

took 1993 Ranger Bass boat to lake started engine engine is a(2.5 mercury 200hp) engine had a knocking noise I shut engine off then restarted there was no knocking noise but blew a head gasket, what was the noise? and why did it blow head gasket? thanks

Answer 1

My question is when i'm in the water ad i go and push the trottle up to go faster it goes right down.What can be the problem?