2007 Caterpillar C18 FUEL BURN

[CFPAC]

Hi ..Based on these numbers below.....

Speed Consumption per hours Range RPM

Maximum: 15.0 knots 60 US Gal/hr 1,700 NM 2,250 rpm

Cruising: 12.0 knots 46 US Gal/hr 2,000 NM 1,800 rpm

Economical: 10.0 knots 28 US Gal/hr 3,000 NM 1,500

　 Could anyone tell me using the above as a base what 6 or 8 knots would look like? Range/ USG per hour at what rpms? Also with twin Cat C18 engines Would it be possible to run then continually 24 hours a day for approx. 2 weeks? Would it be safe to run low rpms to get 6/8 knots for this length of time?
Any suggestions and advice would be appreciated
Cheers