I was trying to picture a 7 ft kayak so I had to do a search. Whitewater kayaks are close to this length, but usually a little longer. For examples see

http://themountainshop.com/whitewater_kayaks.htm

As in Paul's excellent post above the depth will have to be greater. There are some line drawings at

http://www.arctickayaks.com/plans.htm

for a Koryak at 8' 5.8" length 24.8" beam, if you are in need of ideas. The waterline is shown for a 150 lb man. So you would have to shorten, widen, and deepen it. An offset table is given in the pdf file. Perhaps you can try one of the free software programs to design and calculate the displacement for the given load? Hulls and Bearboat are two examples. Hard to say how it would handle though. How do you plan on using it?

Paul

: I would like to build a 7 foot kayak, will this hold my weight i weight 178
: the beam will be 28 in. wide. will this hold me?