Engine gear drive?
 

Why is it I never see gear drives runnig in boats. Would they not hold up better after tons of hole shots keeping correct timing?

decent timing sets (chains) do a decent job by themselves. Only at high rpm with huge cams and stiff valvesprings do they fall short. In those cases, belts are the answer, since the belt will dampen the harmonics better than anything else. If ignition timing is your concern, there is no better answer than a crank-trigger setup. ALL cam-driven timing triggers will suffer from spark scatter if the cam is not restrained from walking front and back in the block (thrust bearing behind sprocket and needle button against timing cover) even if it is driven by a gear. You simply don't see much use of gear drives except for the novel noise they make - which is a cool noise.

I can't see that longevity would be an issue. If that is your concern, just go with a better double-roller premium chain and billet sprockets.