Use Lloyd's Register weld factor 0.44 to 25 mm , this gives a double fillet 11 mm (throat!).As ship plan approval surveyor I have seen larger fillets in seafastenings..
regards,
Femarie
Just take 0.5 g athwartships (ay), o.2 g in longitudinal direction(ax) and 0.3 g =az(total 1.3) vertically.
Applied these factors before when transporting crawler cranes on barges from europe to north africa.
In case of high deck cargoes use 0.65 g for ay.
regards,
Femarie