Hi Ian yeah your right its about 19.5 cm long and yeah masking off is gonna be a complete pig to do, but itll be worth it.
One thing about that uboat site is i started a search for the ship my grandad was on in WW2 it was a merchant navy ship but i dont know the ship name and my grandads name brings up nothing. All i know is that my grandad was 18 years old and on look out for uboats in the crows nest (i think thats right anyway) and he fell alseep on the job and yep the ship was torpedoed and sunk, my grandad and 9 others incuding an officer were on an open raft for 2 weeks and prusumed dead, the officer even had to draw his gun on my grandad to stop him drinking sea water i then belive they were picked up by another ship. I recently lost my dad and i got my grandads medals just a navy star and sevice medal (they were the one thing i wanted) but i know there was a newspaper arcticle with all the details about the incident which my nan had hanging on her hallway wall. I know my dad had a copy of this article but at this moment in time its stuck in a box in teneriffe (my dad retired there) and his (remarried) wife keeps forgetting to get it for me. Ive just emailed one of my aunties to see if she knows the name of the ship, so fingers crossed.