They do not see the philosopher's skill as anything of importance because they can not comprehend the forms like the perceptive philosopher who is constantly questioning the society to make it a better place for all citizens. .
All on board the ship see the navigator as useless because they do not understand the obligations of a true navigator and what is involved in his art. The navigator's skill looks at the weather, seasons, stars, and the wind; and knows what is going to happen long before is does, because that is his skill. Unfortunately he is unable to do anything about the future or the crew because he is not is a position of authority to do so. The navigator wants to be in a position to help not only himself but also the entire crew of the ship. He is not the biggest or the strongest and if he speaks up they will kill him and throw him overboard because he is eating food and getting paid wages that could be extra for them.
The navigator represents the Socrates" idea of a philosopher king and more accurately his attitude towards democracy. The philosopher longs to steer the society safely through dangers waters, and knows what is going to happen if he does not, that Athens will crash and sink just as this ship. Once that happens they will be under a tyrannical rule of some foreign invaders again. Plato feels the same way as the navigator, he wants to speak up to help Athens become a better place for all its citizens but if he does he fears that his end will be the same as Socrates, and he does not want to be a martyr.
Socrates is trying to explain how an uneducated society thinks foolishly of the one who has knowledge/wisdom in philosophy and governing. The politicians form small power groups in order to control the society as they see fit for their own benefits. The people of the society are persuaded to see no use for the navigator; also if he does speak his knowledge will fall to deaf ears.