when are you yanks going to convert to metres (LOL) - here goes! I assume the measurements you've given are for the 1/1 Hunley (what ever that is!)
L39.5feet = 474inches (in 1/1 scale), so 474 divide by 32 = 14.8125incles (in 1/32scale)
W4feet = 48inches (in 1/1scale), so 48 divide by 32 = 1.5inches (in 1/32scale)
I don't know if this is right cos I don't know the sub Hunley (I must be having one of those mental blocks!!!) Never seen a photo of it with someone standing next to it, so It's hard for me to get a mental picture of the size!
Hope this helps Pat!