How can I get the boats to be placed in the matrix without touching?

The two 1 represent a ship, the two 2 represent a ship and the two 3 represent another ship. the boats have 2 cells of size and must be placed using random and without touching.

How can I get the boats to place themselves in the matrix without touching each other?

    public void crearTablero() {
    int numero = 0;
    System.out.println("    0  1  2  3  4  5 ");
    System.out.println("   ------------------");
    for(int i = 0; i < tablero1.length; i++) {
        System.out.print(numero + " |");
        numero++;
        for(int j = 0; j < tablero1[i].length; j++) {
            System.out.print(" " + tablero1 [i][j] + " ");
        }
        System.out.print("|");
        System.out.println(" ");
    }
    System.out.println("   ------------------");
}

    public void colocarBarcos() {
    int barcos = 1;
    do {
        int orientacion = azar(3,1);
        if(orientacion == 1) {
            vertical(barcos);
        }else{
            horizontal(barcos);
        }
        barcos++;
    }while(barcos < 4);
}
    public void horizontal(int barco) {
    int x;
    int y;
    do {
        x = azar(6, 0);
        y = azar(4, 1);         
    }while((comprobar(x, y) == false) || (comprobar(x, y+1) == false) || (comprobar(x, y-1) == false));
    tablero1[x][y] = barco;
    if(azar(3,1) == 1) {
        tablero1[x][y+1] = barco;
    }else {
        tablero1[x][y-1] = barco;
    }
}

public void vertical(int barco) {
    int y;
    int x;
    do {
        y = azar(6, 0);
        x = azar(4, 1);
    }while((comprobar(x, y) == false) || (comprobar(x+1, y) == false) || (comprobar(x-1, y) == false));
    tablero1[x][y] = barco;
    if(azar(3,1) == 1) {
        tablero1[x+1][y] = barco;
    }else {
        tablero1[x-1][y] = barco;
    }
}   

public boolean comprobar(int posicion1, int posicion2) {
    boolean comprobar = false;
    if(tablero1[posicion1][posicion2] == 0) {
        comprobar = true;
    }
    return comprobar;
}

    public int azar(int maximo, int minimo) {
    int azar = (int) (Math.random()*(maximo-minimo)+minimo);
    return azar;
}