power problem

[beau]

i am having a problem.
I have recently launched my 40 ft power trimaran with two, thirty hp Honda outboards and performance is well below what it should be.
With one motor at 3,000 rpm I get 6 knots with both motors at 4,500 rpm (maximum revs) I only get 8 knots.
Now before you all say 8 knots is OK for a 40 ft boat you must understand that this is a very slippery hull which weighs in at 5 tonne. At 8 knots there is NO sign of a bow wave, the water flow is very smooth and flat even the stern wave is flat.
The motors should rev out at 6,000 rpm but stop at 4.500rpm with standard props. Everyone wants to sell me a smaller pitch prop which would get my rev's up. but I do not see that increasing the speed very much.
Any suggestions?
My experience and prototypes that I developed of this design have shown that I should be getting more speed for that amount of power. My last boat a Catalina 25 full keel would do 7 knots with a 10 hp Honda outboard before a bow wave formed and hindered further speed.