Motor sizing Issues

Hi guys
im no expert but this just doesnt seem right to me,
Using CAD ive designed a basic hull outline which ive then imported into a CFD package to optimise the drag values.
The Boat is a catamaran design the hull is roughly 9m LOA 1m Beam 1.5m depth and weighs approx 1800kg, without batteries or motors.
From CFD i found the drag to be approx 300N using single phase flow (just the submerged part of the hull)

Now using the instructions on this website
http://www.solarnavigator.net/hull_drag.htm

calculated the required HP required to 2.75HP @ 7knots which relates to just over 2kW power.

Now ive always liked the lynch electric motors so i chose a 3kW motor...which is startlingly small for the size of the boat

Am i just being paranoid or are my calculations completely wrong

PS this is a university assignment im not actually making a boat..just create and analyse the system

 

You are multiple posting. This will make it very hard to answer your questions because they will be spread out in several threads.