A while ago I talked about the size of the Targaryen fleet at Dragonstone (if it existed at all)and assumed it with 5000 man. This is what I have found out so far:
1. there was a fleet according to the myths Dany was told
She had been born on Dragonstone nine moons after their flight, while a raging summer storm threatened to rip the island fastness apart. They said that storm was terrible. The Targaryen fleet was smashed while it lay at anchor, and huge stone blocks were ripped from the parapets and sent hurtling into the wild waters of the narrow sea. Her mother had died birthing her, and for that her brother Viserys had never forgiven her.
2. about fleet sizes:
"In the Free Cities, there are ships by the thousand," Dany told him, as she had told him before. "Wooden horses with a hundred legs, that fly across the sea on wings full of wind." A Game of Thrones - Daenerys VI
He sang of Jonquil and Florian, of Prince Aemon the Dragonknight and his love for his brother's queen, of Nymeria's ten thousand ships. - A Clash of Kings - Sansa VI
Lord Gylbert began to speak. He told of a wondrous land beyond the Sunset Sea, a land without winter or want, where death had no dominion. "Make me your king, and I shall lead you there," he cried. "We will build ten thousand ships as Nymeria once did and take sail with all our people to the land beyond the sunset. There every man shall be a king and every wife a queen." A Feast for Crows - The Drowned Man
"A thousand ships?" Ser Harys Swyft was wheezing. "Surely not. No lord commands a thousand ships." A Feast for Crows - Cersei VII
"Can we walk across the waves, ser?" asked Lysono Maar. "I tell you again, we cannot reach the silver queen by sea. I slipped into Volantis myself, posing as a trader, to learn how many ships might be available to us. The harbor teems with galleys, cogs, and carracks of every sort and size, yet even so I soon found myself consorting with smugglers and pirates. We have ten thousand men in the company, as I am sure Lord Connington remembers from his years of service with us. Five hundred knights, each with three horses. Five hundred squires, with one mount apiece. And elephants, we must not forget the elephants. A pirate ship will not suffice. We would need a pirate fleet … and even if we found one, the word has come back from Slaver's Bay that Meereen has been closed off by blockade." A Dance with Dragons - The Lost Lord
Out on the river, Bold Wind unshipped her oars and glided downstream in the wake of Seaswift. Last came King Robert's Hammer, the might of the royal fleet. . . or at least that portion that had not fled to Dragonstone last year with Stannis. Tyrion had chosen the ships with care, avoiding any whose captains might be of doubtful loyalty, according to Varys . . . but as Varys himself was of doubtful loyalty, a certain amount of apprehension remained. I rely too much on Varys, he reflected. I need my own informers. Not that I'd trust them either. Trust would get you killed. A Clash of Kings - Tyrion IX
With four times as many ships as the boy king, Ser Imry saw no need for caution or deceptive tactics. He had organized the fleet into ten lines of battle, each of twenty ships. The first two lines would sweep up the river to engage and destroy Joffrey's little fleet, or "the boy's toys" as Ser Imry dubbed them, to the mirth of his lordly captains. Those that followed would land companies of archers and spearmen beneath the city walls, and only then join the fight on the river. The smaller, slower ships to the rear would ferry over the main part of Stannis's host from the south bank, protected by Salladhor Saan and his Lyseni, who would stand out in the bay in case the Lannisters had other ships hidden up along the coast, poised to sweep down on their rear. A Clash of Kings - Davos III
3. about men to ship ratios
"How would the queen suggest they accomplish that, without sufficient ships?" asked Ser Loras. "Willas and Garlan can raise ten thousand men within a fortnight and twice that in a moon's turn, but they cannot walk on water, Your Grace." A Feast for Crows - Cersei VII (regarding the thousand ships of the Iron Fleet)
- the Arbor has the largest "Lordling fleet"
- no Lord has a thousand ships, that may include "Lord" Euron. The quote really works in both ways, arguing against his ship size and against a possible counter.
- a general ship to men ratio for all types of ships may be 100
- Even the relative "small" invasion of Connington needs a (pirate) fleet to support.
- A large part of the royal fleet fled to Stannis, Stannis had 200 large combat ships and a lot of smaller "cargo" ships
- a thousand ships is a possibility for rich city states though. (And I count Oldtown towards it)
- The Baratheon royal fleet is only 15 years old, that is not the lifespan of a wooden warship. The Targaryen fleet can include ships from a much larger timespan
- there is no knowledge about the size of a royal fleet, it is clear that it could "in theory" have a thousand ships, a more grounded calculation may include 100 warships and 400 other ships from the crownlands.
- I tend to go the Feather way of the mirror for reasons of simplicity and conclude that Stannis fleet is the fleet size of the royal fleet, which included 4600 transported infantry.
- Overall I still think my guess of 5000 sailors is very possible and very grounded. If I just assume 100 warships in the royal fleet (which is the size of the Baratheon royal fleet) and downsize the sailors to 100 per ships (they are larger warships though, the King Robert's hammer has 400 oars), I would come to 10.000 men.
So my conclusion, that a storm that grounded the royal fleet, would have left a sizeable defence force at Dragonstone, still stands. We know that the attack:defence ratio for castles is 4:1 - 6:1. So Stannis should need at least 20k men upwards (for a larger army) to take a defended Dragonstone.
So either there was never a fleet at Dragonstone and the royal fleet vanished or something else must have happened. Even if everyone just gave up, the men would still be stranded on Dragonstone.