Hi everyone I am new here but not new to boating. A little back ground I am 54 live in Panama City, Florida and have been boating since 1980. My other boat is a 1972 Thunderbird Formula 233 I spent 2 years restoring and know every inch of her and can do all the mechanics on those old Mercruiser Pre Alpha drives and old Chevy in line 6 cylinder engines. Because one boat wasn't enough we just bought a 2005 SeaRay 260 Sundancer and starting to really enjoy the cruising lifestyle with the wife and 2 kids. Ok enough background and if I haven't lost you my problem happened today. Took the boat out and no issues. Planed it out and rode around for about 20 minutes, slowed to trolling speed and cruised around the bay at about 6 mph for an hour when I noticed engine idle went down to 500rpm and would not go any faster. No alarms sounding just engine would not go over that rpm. Took it out of gear and same thing and then it quit entirely. Put the anchor out and tried starting it and the engine would turn over and for a spilt second sounded like it wanted to fire up but then nothing. While turning over the engine I started checking gauges and noted I had oil pressure, water temp at around 160 and before anyone asks yes I have fuel just over a half a tank . Then I noticed the Smart gauge showing zero psi on water pressure. All this stuff is new to me and this is the newest boat I have ever owned so still trying to get used to this engine. It has a Mercruiser 350 Mag 300hp tied to a Bravo 3 out drive. It is raw water cooled. I checked the out drive and it wasn't blocked with a plastic bag or grass. I continued trying to start it for about 15 minutes on and off and it finally started and ran. Engine would go over 500rpms now but still showing zero water pressure. I am assuming this is the raw water being pushed up to the engine. Engine water temp still at around 160*. Opened up the hatch and felt engine which was warmed up but certainly not scolding hot so it seemed like it was running at that temp. Ran it back to marina at 1000rpm with hatch open for air flow and watched gauges with no change to water temp, 160* and water pressure zero. Once at the marina had them put boat on the rack and ran engine on the hose. Same result engine temp at around 145* and water coming out where it should but still zero water pressure on the gauges. So any guesses and sorry for such a long story.