I built a Minimost with my son when he was 14, and another like it with my grandson when he was 14 (still ahve that one) similar to the one you posted photos of. How much motor depends on how fast you want to go and how close to the edge you want to run. I started my grandson with a 6 Hp Evinrude until he got the hang of it, watching waves, etc, then moved him to a 9.5, then a 10. The 6 did plane it off, once you put your hands out on the deck to hold it down until it built up speed. He’s grown now and in the Air Force, but Grandpa has plans to drop a 15 on it next summer to run himself. Al these are stock, and with a stock 15, it should do around 40 MPH – fast enough for me at age 70, but I still water ski too. My son raan a KE7 Mercury (10 HP advertised but put out 12 to 14 when the RPMs get revving high). Note that motors set up for racing these light boats have a skinny lower unit with special gears and props to get the speeds mentioned in the post about the various classes of hydros. When you are a few inches off the water in a boat this small, picking your way through the waves, and leaning into corners, 20 MPH can feel like 50. With boats like these, you learn pretty fast how to get motors going again after they get dunked. On the smaller hydros like the Minimax, keeping motor weight down is desirable.
There are many boat plans online. The two main sites are below – both have several hydroplanes, and just about every other boat you can build with wood. Most of these plans originally appeared in magazines like Popular Mechanics in the 1950s.:
Dave
