My plank bender comprises a 4 foot lenght of plastic waste pipe sealed at one end and with a removable cap to fit the other end - see photo - (all fittings courtesy B & Q or similar outlet). I'e also got a 2 foot version for use with short planks.
Planks are inserted into the tube, fill with common household ammonia (always do this in the open air and use rubber gloves and eye protection) following which the open end is capped. After approx. 15 minutes remove planks one by one, rinse in cold water - in the open air - then pin/clamp in situ to dry thoroughly (always position a pair, one each side of the hulll, to eliminate the risk of warping or otherwise stressing the hull). When dry the planks will conform to the hull's curvature where they were positioned when wet, and can then be permanently fixed
I've found this method ideal for all common dimensions of 'modelling' stripwoods, including 3/8th x 1/8th cedar planking used on my current scratch build square rigger .
