Hello Mike
The hull timber looks like pitch pine in which case the staining will be deep within the grain and very difficult to remove. Vintage pond yachts were often made from pitch pine as it was easy to work and fairly cheap, the downside of pitch pine is the need for filling the grain prior to painting (hence the staining)
As the hull is already shaped I think that a power sander might do more harm than good as you run the risk of creating flat spots I would recommend simply using a fine grit paper and sanding gently by hand and then use a filler / primer paint to smooth out the standing grain.
Paul
Edited By The Fat Controller on 22/05/2012 07:20:40