The diagram shows the parallelogram OABC. Given that \(\overrightarrow{OA} = \mathbf{i} + 3\mathbf{j} + 3\mathbf{k}\) and \(\overrightarrow{OC} = 3\mathbf{i} - \mathbf{j} + \mathbf{k}\), find

1. the unit vector in the direction of \(\overrightarrow{OB}\),
2. the acute angle between the diagonals of the parallelogram,
3. the perimeter of the parallelogram, correct to 1 decimal place.