This may be over the top, but I think the base idea is good. Questioning the costs and duration.
Name: Poseidon's Fleet
Rarity: Legendary
Type: Instant
Target: Player (Yourself)
Casting Turns: 50 + Extra
Duration: 1 Hour
Extended Duration: +1 Hour for each 50 extra turns used
Max Duration: 3 hour
Witch Hut Recipe:
3 Commandeer
3 Flying Dutchman
7 Tide Waves
2 Call the Kraken
Crafting Time: 96 hours (4 days)
Crafting Cost: 1,000,000 gc
Crafting Restrictions: Player can only possess 1 in inventory
Effect: Control of Poseidon's Fleet for x Time.
Fleet can instantly travels x times for free. (x = # of Flying Dutchman used to craft.)
Fleet consists of 2 Level 10 Man-of-Wars, 3 Level 11 SoTL with Full stats.
Fleet can't be plundered. (Players cannot capture the ships through plunder.)
Damage is non-repairable. Once Health reaches zero, the ship/fleet disappears into the depths.
Fleet returns to the depths at the end of the duration.
Description: You have summoned the fleet of Poseidon. It's power is unmatched and uncontrollable. Use it wisely.