System ship travel

Has anyone worked out how long it takes a system ship to travel various distances, including acceleration and deceleration? I could use the ship travel calculations from <i>GURPS Spaceships,</i> but it would take some conversion. Even a simple rule of thumb would be welcome.<div><br /></div><div>The rule on page 12 of the <i>Knight Hawks</i> campaign book about saving fuel by traveling at 10,000 km per hour is obviously wrong: going from Earth to the closest part of the middle of the asteroid belt at that speed, neglecting acceleration and deceleration, would take five and a half Frontier years.</div>