Ok to start I just bought the boat and its my first. it is a 96 scarab 22 with 454 gen 6. the motor looks pretty new I think it had a small block from the factory. The engine looks to have new cap and plug wires. has an accel coil. It has a non marine carb on it but I don't think its the problem.

What happened- after cruising for about a half hour through some good chop the boat died just like I shut the key off. looked in the engine area and saw a melted negative battery terminal. we tried to hold the cable on and restart but there was a no spark issue so it just cranked and cranked. Got towed to the marina and the boat sat there over night went back the next day and if fired right up but only ran for about ten minuets then died no spark again. got the boat home found a loose connection on the starter. fixed that and put new terminals on the battery. Took it out again ran fine for 30mins and we tied up, we left it was running fine for about 30 then it died again, let it set 30seconds and it started easy. as soon as I got on plane it died again let it sit for 30secs again and it started fine. drove straight to the marina and it ran fine. the fuel pressure was bouncing between 6 and 12 psi which it always does.
Any help is much appreciated im going to change the coil and check for more loose connections!

You need to post what you have here - MPI or TBI or carb and a serial number for the engine

is your ignition OEM stock if not what is it ?

Fuel pressure bouncing all over the place is another problem as well

Its a holley carb not marine. Im 99% sure its stock ignition other than accel performance coil. I have two modules at the rear of the distributor. I thought there was suppose to be one on the riser but I don't have it there. what could cause fuel pressure problem when under load?

and I don't have the number on the engine but the rocker arm plates have mark v on them so I assume it is gen 5 thunderbolt ignition

Feel the coil the next time it dies,,my guess,the coil.

I bought a new coil. Someone suggested running with a seprate fuel tank but if it was bad gas it should be fixed. And if it was clogged or broke tank pick up it would do it all the time?

It's not fuel issue

I would suggest start at the battery and trace both ground and positive cables. Make sure all connections are clean and tight and your ground battery cable is attached to the block. Next check connections on the alternator connections, 90amp fuse on starter along with wires connected to fuse. Then look all over the rest of the motor for loose connections.

Checked all connections the first time it died. the main plug on the engine is tight. alternator connections are tight. I do not know this 90amp fuse is? I can let it run in the yard for as long as I want and rev it and it runs great. I tried moving and jiggling the wires while it was running and nothing happened. Maybe Vapor lock?

You wouldn't happen to have a GM Hei distributor on it would you ? If so, sounds like a classic ignition module issue.

Psst: I'm taking the 'no spark' comment by you literally.

edit in: find out what is causing your guage fuel psi to bounce...be it sender/guage, pump, or more schitty wiring.

I think you have multiple issues that need to be fixed correctly to narrow the problem down.

12psi of Fuel pressure on a non marine carb is a serious safety concern. Max should be 7psi or so.
Marine carbs are designed to dump excess fuel into the carb. Automotive carb will spill fuel all over.
This combined with burning wires and shorts is a dangerous combo.