As for an outboard tunnel I would recommend 34" or larger using a K&B .45 outboard lowerhttps://www.mecoa.biz/shopdisplayproducts.asp?id=148 part #50-4803
and a Hypeformance
https://www.offshoreelectrics.com/pr...pi-eobck75-5mm
A lot of smaller tunnels have been converted using P/limited motors. They are fast but tend to go upside down easily. The larger hulls will be much more seaworthy. I would recommend not going larger than a 40mm X 74mm motor. 4S around 2000kv and 6S 1250-1600 kv. I have a 36" Vision that holds records with a larger motor but staying with a 40X74 1600Kv on 6S using a cheap 150amp ESC will still run 50+mph easily. Stays on the water and plenty fast. You can always power up later but staying conservative will make it easier to set up and prop correctly. You need a 180 + oz of torque servo to steer.
https://www.offshoreelectrics.com/pr...od=pow-lw-20mg (minimum)
Hope this helps.
Mic