Here's what's next. Go talk to Professor Elm in New Bark Town and get the SS Anne Ticket. Then head to Olivine (Asagi) City and enter the SS Aqua through the passage that was previously blocked by a guy.

Now that you're on the SS Aqua you can go around battling the gym trainers aboard. To get off you first have to find a man's granddaughter who is with the captain of the ship.

To get there you must find a lazy Sailor who is in the room next to yours. Battle him so you can get past another Sailor blocking your way later in the ship.

Find the girl, and you'll be sent back to the Grandpa's cabin. He'll give you Metal Coat for your troubles. Metal Coat increases the strength of Steel attacks.

Note: If you decide to go back onto the SS Aqua for a second time you must go to your room and sleep in your bed if you ever want to get off the boat again.

Lt. Surge's Pokemon shouldn't be too tough. Especially if you have a Ground Pokemon like Graveler or Sandslash. Dig or another Ground type move should render his Pokemon helpless.

After you beat Surge, he'll give you his Thunder Badge which will increase your Pokemon's Speed.