Contract of affreightments are contracts of charterparties including the bills of lading. However, charterparty and bills of lading (BoL) are not the same. Where the charterparty is ‘the’ contract in essence, bills of lading is considered to be the document evidencing that particular contract.
There are distinct differences between the charterparty and the bills of lading.
A charterparty is used for full shipload of goods, whereas a BoL is used for less than full shipload. The services used are also different like a ‘tramp service’ for charterparty and ‘liner service’ for BoL. For charterparty common law applies, but BoL is governed by international rules like the ‘Hague-Visby Rules’. Charterparty is the contract for carriage of goods which governs the commercial relationship between the charterer and the shipowner and the BoL is issued under that contract as per the terms of the contract.
This is a summarised version of a detailed explaination given by John F Wilson in Carriage of Goods by Sea, 6th edn.