I have that same riverboat sharpener....
I agree, you need some more lights, your placement is fine but lighting needs an overhaul.
Lighting for this stuff can be as basic as can be as long as the basics are covered. for all my white BG'd stuff all I used was two table lamps and one overhead celing light, all with flouresent bulbs and a white sheet of paper.
i was using 1 table lamp and a ceiling light and a sheet of poster board. thanks, and thanks for that link jeroen.