Ive never built a tunnel hull and know that those have peculiarities in the setup.
Check out the forums and look for others who run tunnels then adapt it to your size.
Electric boat motors generate more torque than car motors in general.
So it's possible the 380 nikko motor may not produce what a 400 Graupner would.

From these and the other pics I can only give you a few considerations:
1. You may be suffering drag from the hull bottom and hardware
2. Most other hydros I've seen have their hardware alot closer to the transom
3. Verify what the center of gravity should be for a tunnel hull of that size
4. Check your weight, the setup could be too heavy for the motor

Suggestions on a setup I would not feel comfortable giving since I've never had a tunnel hull but take a look at this thread [link]http://www.rcuniverse.com/forum/m_3704981/anchors_3728392/mpage_1/key_/anchor/tm.htm#3728392[/link]
Also check out [link]http://www.microhydros.com[/link]