mercruiser v6 overheated

CONFUSED!! I just got my boat back after getting a normal service,oil change, gaskets, New impellor, Some new bellows, also had to replace Engine Coupler because it was worn , I also got some guages fixed(Temp Guage, Tacho etc)

when I got the boat back, I took the boat out and after about 20mins I notice A lot of smoke coming from the engine, I opened the engine cover which was so hot to touch, when I inspected the engine I notice a lot of white to light blue smoke coming from the hoses that come out of the rocker cover that lead into the carberettor. The temp guage was at half. I quickly turned off the engine as theire was that much smoke I thought it was going to blow up. I waited for a bit then started the engine back up (no problems) when I gave her some acceleration I heard a clunking sound(clunk clunk clunk) so I backed it of and just limped her into dock

I took the boat to the marine mechanic who checked the thermostat, the water pump, all ok ,he could smell a lot of oil so he did a compression test

cylinder 1 = 190 cylinder 2 = 160 cylinder 3 =190 cylinder 4 =190
cylinder 5 =190 and cylinder 6 = 150

He also noted a little bit of water in a couple of the spark plugs. He said that it looks like I have blown some rings,(I spoke to another mechanic) and he said because of the clunking sound I could have done the big end.

My question is this!! HOW DID THIS HAPPEN and WHY (the motor is a rebuilt motor from about three years ago)and do you think this is what is wrong. Could alot of sea weed have caused this?

Help

 

No worries guys, I went and purchased a new motor

 

Sounds like they bolluxed up the replacement of the impeller in the outdrive and the engine starved for water and the head gaskets gave up the battle. Water in the combustion chamber is a pretty sure sign of head gasket or intake failure.