Am tee-ing up the first keel here, although prior to doing so I've had to shave some 20mm off the forward end of each deck to suit. In the US when you're buying 4' by 8' sheets of anything they are likely to be the stock measure. The use of metric tho' in different parts of the world means that there are endless variations on the perfect match of 1220 x 2440mm.
I've used the backer-board (aptly) to back the keels, whereas the decks are topped with ply. The latter conforms to that conversion metric, the former does not. In fact it measured 600 x 1200mm at the get-go, hence the required adjustments this morning. Elsewhere I have seen sheets 2500mm long by 1250mm wide, so what I do is to treat it like a box of chocolates, as Forrest Gump would.
