well its like this...
im a welder/fitter by trade i did a auto-cad drawing of the tuned pipe to get dimensions and im making one out of stainless to suit where the engine sits as posted in photos. im gonna turn up a cooling jacket on the lathe at work to solve the heat problems. anyone got any ideas on where to stat in regards to props i checked out a octura prop chart and a x472 or x482 was a ballpark start for over 30cc motor but they r only 2 blade i wouldnt mind a 3 or 4 blade any ideas anyone???

Woodie your spot on about the exhaust it totally never crossed my mind,when he comes to tilt the engine for exhaust clearance the carb will be moving even closer to the hull bottom which takes us back to the low centre of gravity question i mentioned before.For clearance won,t the engine have to be lifted up?There,s lots of problems to overcome which is probably why nobody has used this engine before unless of course im wrong in which case i would like to see a completed boat to see the engineering involved.With regards the props my guess is that motor will pull anything so i would personally go big but im no expert so the more experienced will advise better.This topic has certainly got a lot of us thinking & i look forward to other comments.Thanks DAZ

Check out ABC props .... 3016/3 3116/3 3216/3 should be doable running 49cc's

just a couple of pics of the boat trailer im buildin for the big girl im gonna tow it around on the back of my brushless traxxas revo