Whilst I am not too convinced that the RN had a rounded collar white front, I admit that I have not been able to find any evidence to the contrary. The only picture of a uniform is from WWI and the model is wearing a square collared white front. unfortunately a friend who has done a lot of research into naval customs cant help with this either.
David
The flap thingy is called a collar
See below on history of the collar and also regarding protection from tarred pigtails.
Sailor's Collar
The sailor's collar deserves a special mention. Tarred pig tails disappeared rapidly after 1815 and the last is recorded as having been seen at sea in 1827. On the other hand, the first broad collars were worn after 1830. Contrary to popular belief, therefore, the two were never worn together. The first collars were not cut square but were round and closely resembled items that were fashionable ashore. The three rows of white tape were probably added for ornament at first, surviving records mention some discussion about whether there should be two rows or three. The more familiar square collar developed as it was easier for the men to cut and sew themselves than the round variety.
Source:
http://www.royal-navy.mod.uk/server/show/nav.3772
I have to confess that even though I was a matelot. I too was under the impression that the collar was introduced to protect the uniform from tarred pigtails. But I guess the Royal Navy website is a more authoritative source.