At 25 m you are in the realm of wooden shipbuilding. There is almost nothing that is transferable from small boat, trip-building technology.
Besides being aware of the interior loads and the expected exterior forces you have to consider the leverage of all those oars bearing on the sides of the boat. You need either someone who is experienced with building these boats or a competant engineer to run the numbers. As a do-it-yourself project you are stepping into the unknown.

: Has any body got a clue if there is something like a maximum lenth to which a
: canoe can be built with 0.75 x 0.25 inch strips. And if construction wise
: there is a limit could it be increased by increasing the size of the
: strips? The reason I am asking is that I have plans of constructing and
: building a dragon boat to be crewed by 50. (double rows of course) The
: ideal length of this boat would therefore be about 25 meters. If the boat
: would have enough rigidness in some way or another the handling in and out
: of the water would be no problem.

: regards
: Arthur