This has happened a few times. When ruining wot for 30 seconds or more the boat just shuts down. . like all power is killed to the ignition. It sits for a minute or so then everything comes back to life. Seems like there is a breaker tripping and then automatically resetting. Are there Auto resetting Breakers somewhere? This is a MerCruiser originally had a 454 now as a 540.

what ignition, distributor, coil are you running

You could also be running it out of fuel. What is your set up?

Had a similar issue years back. Dist cap and rotor had some corrosion and under heavy load engine would just shut down.
It also could be coil or a distributor module that is heating up.

Daytona ignition. Not sure on coil.

A scan tool hooked up while running would have pin pointed right away --- TPS parameters.for your app ^^^^

for the OP it was never mentioned if this was a carb or MPI engine. IMO this is a carb app. More info is needed. Huge difference from carb to MPI engine for shut down issues.

to the OP - what does voltage show at shut down ? voltage on the gauge - voltage across sections of the engine with a volt meter - at the starter and at the alternator - what is voltage readings ??? Is the alternator going bad ???

Next test --- sealed inline spark checkers - do you have spark trying to recrank the engine ? you can even put a sealed spark checker inline for the coil to top of distrib cap - do you have spark ?

Next is it the fuel side - what is your fuel pressure at engine shut down and at trying to restart ?

3 tools here will find your issue(s) or at least where the problem lies.

This is a carb engine. Voltage seems higher than it was before issue started. 15.5 volt if I remember correctly . After the first time it happened I replaced both batteries and the alternator and the problem is still present. It runs great no signs of missing or sputtering it just cuts out 100% when the issue occurs. It seems to me as though something is tripping and then resetting itself when given enough time.

I chased a problem like this some years ago..........it turned out to be the ignition switch of all things, would only do it at WOT go figure.