This of course raises the question of what if the factual situation changes between the time of giving the nomination (and therefore the warranty) and the time when the vessel arrives at the port. Lord Roskill indicated that if a prospectively safe port subsequently became unsafe due to changed circumstances, the charterers had a secondary obligation to issue fresh orders so that the vessel could proceed to a safe port. Since this issue was not essential to the decision of the case in question, Their Lordships did not consider the ramifications of this proposal. In particular, the entire issue of how the doctrine could be applied to voyage charters was expressly left open. Where the charterer has no right to nominate an alternative port, any such implied secondary obligation would be inconsistent with the express terms of the contract so that if the named port became unsafe, it could be argued that the contract had become frustrated. A further problem, both under voyage and time charters, will arise if the charterer becomes obliged to nominate an alternative port, but the Bills of Lading do not contain provisions entitling the vessel to deviate in the changed circumstances which have arisen. It can be seen, therefore, that the position remains unclear.