clutch ideas for 3m craft using 3x90cc 2stroke engines

hi there every one this is my first time in here.and i got a few questions for ya
i have built a craft 3m long. the front is pointed and raised about 20cm from baseline. the bottom is flat. total displacment of craft is 180L. total weight of craft, rider, fuel, engine etc is 100kg-130kg. total expected water contact at top speed is 3sqfeet not inc prop.
The prop is 3bladed 9x6 and is powered by three 90cc lightweight 2stroke engines running at 6000rpm(ish). there linked together by spoket and chain. engines are position two side by side the right way up and one tucked in behind upside down to save space. i have conected the exhausts from all three into one tube three times the bore of the origional and have done the same with the air intakes for the carbs.
1 any idea how fast it will go at 6000rpm 5000rpm 4000rpm 3000rpm 2000rpm

unfortunatly the engines are air cooled. this is unfortunate because they need to be covered at all time while at sea due to the nature or the craft. i plan to overcome this by making a shroud around the top end of the engines(where the cooling fins are). link them with hose and drive water round them with a small water pump. ill power the pump off the main drive. so when the revs go up so will the flow.
2 will this work any ideas

the engine at the rear is kick start. engin,center fugal clutch then sproket. this by chain turns the other sprokets which are welded direct to the front two engins hopefully starting them.
3 will this work any ideas

the three engin sprokets drive a fourth, this is on a heavy center fugal clutch from a 8hp heavy duty lawn mower.
4 will this clutch slip. and will it have to spin to high to grip causing a sudden jolt of forward movment.

please help me i know all you lot are wicked at this stuff i know the info is basic but im not an enginer but its been my dream to make this craft for years and..... please help