Combine of IF function and Index function with two different tables

Dear Friends,

Good Day,

I have query with combination of IF function and Index function. 

I have prepare a worksheet regarding with my workplace. I need to select the value from two different table with one condition.

Ex: There is 5 different vessels namely A,B,C,D,E these vessel having two different thickness value (Group I Thickness & Group II Thickness), now the condition is "a" is less than or equal to 0.002 use Group I Thickness otherwise use Group II Thickness values. From the dropdown if I select the vessel name the corresponding thickness value will be display in Final thickness cell.

I have attach the workbook for your further reference.

Please suggest me the best answer to complete this workbook am awaiting for your valuable suggestions.

Thanks

Rajaram V