Bearing in mind the conning tower, and top part of the hull was painted in lighter shade than the bottom of the boat i used the Tamiya Medium Blue (XF-18) for preshading this areas.
Mixed at 50/50 with Tamiya Thinner, and sprayed at 20 PSI using the old trusty Badger 200.

Field Blue (XF-50) was applied to lower part of the hull: