Easiest way is just order the fourth rib. If you have a table saw, all you need is the plans. I don't, so I ordered the plans, stems, and four ribs.
Plans, stems, and 4 ribs don't run much for how good they are and how much they gain you.
Federal Minimum Wage (thank you lefty libs :twisted: ) is $7.25/hr.
Some States also have mandated minimum wages higher than the Fed: (: http://www.dol.gov/whd/minwage/america.htm
The income tax laws screw the real earnings numbers up pretty good against solid figuring, though - we have this...
I went with Uncle Johns plans http://www.unclejohns.com/boat/plans/ki ... 5%2009.pdf
Made mine with four ribs and right at 27" on the middle beam. Only used 2 sheets of 4.5mm luan.
You could enclose and foam the ends for some extra flotation, too.