my buddie is about done with his 575s he cant get two weekends out of them they are 03 575 with its boxes, we had one of the first 100 made in our 00 382 and didnt have much luck either but we got at least 20 hrs out of them, any body else have same problem or solution?

Mine run great!
More info might help. You post is vague.

03 575 ac plugs foul out 5 10 hrs he tryed ngk plugs got 2 hrs they load up when cold . i think its the ecu needs reprogramed, if he gets them to clean out it starts fine after its warm but plugs still needs replaced loses high rpm, hes thinking msd ignition. he just got boat last season came from mich now in loto but the problem is getting worse.

Sounds like an ignition problem. Did the voltage on the boat ever drop below 11.5-12 voilts? If so that can damage a MSD igintion in a heartbeat. I speak from experience,

May very well be ignition only. Due to my personal experience, has he ever changed the head gaskets? Known issue discussed here before about the weak gaskets. Stock gaskets are junk, just a matter of time even without detonation. My 02 ran great for 175 hrs. no problem but then lost the gasket completely between 3 adjacent cylinders. On tear down the gaskets had been burning through on every cylinder. I use the NGK V power plugs. I think either a 7 or 8. Earlier head gasket change for me would have saved me a complete engine rebuild.

The stock idle calibration is pretty rich. If his transom is sooty, he probably has the stock settings.
I have a MSD6M box on mine, and the ECU has been recalibrated to lean it out. Rarely if ever a fouled plug. I am using NGKs also.
Zahndok is right on the stock head gaskets. They are standard GM graphites. Why Mercury used these in a supercharged application is beyond me. I bet 75% of their warrantee claims on the 575 were due to these gaskets blowing. Put in a good set of Fel-Pros or Cometics and you should be good to go.
Re ECU reprogramming, AZSM has kit that includes a reflash, higher PSI (6) blower pulley, and a MSD 6M box.
Eric Betty @ EB Marine (Nashville,TN) can do this for you too. I also hear good things about Mark at Precision Marine.
Regards,
Steve

thanks a compression test should show the gaskets bad ? i know it had one side rebuilt already before he purchashed, no idea why, both are haveing same issues.

Try these plugs: NGK UR-5's.