FL-3000N can be good choice
As I have frequently suggested already
Enduranc depends upon patrol speed plus supplies like fuel, food, water etc expect more than 4/5 days in today's navy
https://en.m.wikipedia.org/wiki/Fast_attack_craft
Range: approximately 1,000 nmi (1,852km)
This range at 30 kn would be comparable to e.g. Turkish Kilic / Yildiz / Dogan / Ruzgar classes FAC-M, or French built Combattante II/III class. The
knot is a unit of
speed equal to one nautical mile (1.852 m) per hour
1000 nmi / 30kn = 33.3 hrs = 1 day and 9 odd hours
Clearly, range would be greater at more economical speeds eg.
Type 037 series (China): 2,000 nmi (3,700 km) at 14 knots; = 142.9 hrs= 5.95 days
Combattante III: 2,000 nmi at 15 kn; = 133.3 hrs= 5.55 days
Combattante II: 1,600 nmi (3,000 km; 1,800 mi) at 15 knots; = 106.7hrs = 4.44 days
At economical speed, an endurance of 4-6 days would seem reasonable for this type of ship.
Then again, there is variation in this respect between different classes of ships. For example:
Saar 4.5 class (Israel)
- Speed:
- Maximum: 34 knots
- Cruising: 19 knots
- Range:
- 4,800 nautical miles (8,900 km) at 19 knots (35 km/h); 252.6 hrs = 10.5 days
- 2,200 nautical miles (4,100 km) at 30 knots (56 km/h); 73.3 hrs = 3.1 days
Victory class (Singapore)
- Speed:
- Maximum: 37 kn (69 km/h; 43 mph);
- Cruising: 18 knots (33 km/h; 21 mph)
- Range: 4,000 nmi (7,400 km) at 18 knots (33 km/h; 21 mph); 222.2hrs = 9.3 days
Another example: BNS Durjoy
- Range: 2,500 nmi (4,600 km; 2,900 mi)
- Endurance: 15 days
Clearly, this implies a much lower patrol speed (2500nmi / 360hrs = 7kn)
The fuel economy of the (diesel) engines and the size of the ships' fuel tanks are key in the above calculations.