Beginning from the last quarter of the nineteenth century rapid development of propulsion systems stimulated, in its turn, significant growth in size of the ships. Obviously, a bigger vessel was able to carry more goods and also draw more water but apart from draft limitations, such a vessel required larger sea room for anchoring and safe manoeuvring within port limits, tug assistance in narrow channels, experienced pilot and master to handle it inside the harbour. It therefore became necessary to consider individual particulars of each vessel to ascertain safety of port in question.
G W Grace and Co Ltd v General Steam Navigation Co Ltd  1 All ER 201, per Devlin J at pp.206-207:
…the charterparty, either on its true construction or by implication, forbids the giving by the charterers of orders outside their powers, and, accordingly, that the giving of an order to sail to an unsafe port is a breach of the charterparty.
Once the breach of contract is established, it seems to me to follow that, subject to the ordinary rule of remoteness, damages must result. There may be cases in which the charterer is innocent of any intention to break the contract and where the master deliberately decides to enter a port which he knows to be unsafe. Roche J, on a rather similar point in Portsmouth Steamship Co v Liverpool Salvage Co (1929) 34 LlL Rep 459, indicated that the master should not follow the instructions of the charterer if they lead to obvious danger, but these factors go to the question of causation only. The giving of an order does not necessarily cause the damage that flows from an act done in pursuance of it. Put more specifically, the decision of the master to obey the order may in certain circumstances amount to a novus actus interveniens, but, in the circumstances of this case, the arbitrator clearly regarded the acts of the master as done in the ordinary course of things and not blameworthy. He was doing what any intelligent observer, knowing exactly how he was circumstanced, would have expected him to do.
Per Thomas J in Aegean Sea Traders Corporation v Repsol Petroleo SA (The Aegean Sea)  2 Lloyd’s Rep 39 at p.68:
… I do not think that one can conclude in general that a term as to safety will always be implied into voyage charter-parties where there is an unspecified range of ports. The issue as to whether a term should be implied as to safety and the extent of the obligation may turn on the specific terms of the charter.
Per Lord Justice Morris in Compania Naviera Maropan SA v Bowaters Lloyd Pulp and Paper Mills Ltd (The Stork),  2 QB 68, CA. at pp.104 and 105:
…Though there would have been a breach of contract in giving the order to go to an unsafe place, this would not justify the deliberate act of allowing the ship to suffer damage. The owners must not throw their ship away. If, having the opportunity to refrain from obeying the order, and having the knowledge that the ship had been wrongly directed to run into danger, those responsible for the ship allowed her to be damaged when they could have saved her, it would be contrary to reason if damages could be recovered. They could not be recovered for the reason that they would not be the result of the breach of contract, but of the deliberate and unnecessary act of those in control of the ship. Further, there is a duty to behave with ordinary reasonable prudence so as to minimize damages, and the readily attainable minimum may in some cases be nil. But this does not involve, nor in practice would it be reasonable or convenient, that where charterers have the contractual duty of ordering a ship to go to some place designated safe, and where the ship has the contractual duty of obeying the order, the ship must always doubt the validity of the order and must not proceed until, by making some reconnaissance or by seeking information extending beyond that ordinarily available to a reasonable and prudent ship’s master, there has been a satisfactory verification that a place designated safe is in fact so.
…If it were said that a port will not be safe unless, in the relevant period of time, the particular ship can reach it, use it and return from it without, in the absence of some abnormal occurrence, being exposed to danger which cannot be avoided by good navigation and seamanship, it would probably meet all circumstances as a broad statement of the law. Most, if not all, navigable rivers, channels, ports, harbours and berths have some dangers from tides, currents, swells, banks, bars or revetments. Such dangers are frequently minimized by lights, buoys, signals, warnings and other aids to navigation and can normally be met and overcome by proper navigation and handling of a vessel in accordance with good seamanship.
Per Lord Roskill in Kodros Shipping Corp v Empresa Cubana de Fletes (The Evia),  3 All ER 350 at p.360:
The charterer’s contractual promise must, I think relate to the characteristics of the port or place in question, and in my view, means that when the order is given that port or place is prospectively safe for the ship to get to, stay at, so far as necessary, and, in due course, leave. But if those characteristics are such as to make that port or place prospectively safe in this way, I cannot think that if, in spite of them, some unexpected and abnormal event thereafter suddenly occurs which creates conditions of unsafety where conditions of safety had previously existed and as a result the ship is delayed, damaged or destroyed that contractual promise extends to making the charterer liable for any resulting loss or damage, physical or financial. So to hold would make the charterer the insurer of such unexpected and abnormal risks which in my view should properly fall on the ship’s insurers under the policies of insurance the effecting of which is the owner’s responsibility…
Per Mr. Justice Teare in Gard Marine & Energy Ltd v China National Chartering Co Ltd & Ors  EWHC 2199 (Comm) at paras 101,132:
101 … A port is not saved from being unsafe where, although the vessel will be exposed to a danger which cannot be avoided by good navigation and seamanship, the port has taken precautions designed to protect vessels against that danger but which in fact do not protect the vessel from that danger. If, despite the taking of such precautions, the vessel remains exposed to a danger which cannot be avoided by good navigation and seamanship then the port is unsafe. The charterers’ warranty is of safety, not of reasonable safety. The enquiry in an unsafe port case is not into the conduct of the port authority, for example, whether it has acted reasonably or otherwise. Rather, the enquiry in an unsafe port case is into the prospective exposure of the vessel, when arriving using and leaving the port, to a danger which cannot be avoided by good navigation and seamanship. Of course, aids to navigation, the availability of weather forecasts, pilots and tugs, the quality of the holding ground for anchoring, the sufficiency of the sea-room for manoeuvring and the soundness of the berths and of the fendering arrangements are, as with all aspects of the port set-up, relevant when deciding whether the vessel will be exposed to a danger which cannot be avoided by good navigation and seamanship. But if, having taken into the account the set-up in the port, the vessel will be exposed to such danger then the port will be unsafe.
Critique of Teare J iapproach in Gard Marine & Energy Ltd v China National Chartering Co Ltd & Ors  EWHC 2199 (Comm) ], per Longmore LJ in Gard Marine & Energy Ltd v China National Chartering Co Ltd (Rev 1) (Ocean Victory)  EWCA Civ 16, allowing appeal and setting aside the judge’s order:
50. We consider with all due respect that the logic of the judge’s approach to the issue of abnormal occurrence is flawed. Our reasons may be stated as follows.
52. The import of these passages is clear. A charterer does not assume responsibility for unexpected and abnormal events which occur suddenly and which create conditions of unsafety after he has given the order to proceed to the relevant port. These are the responsibility of the ship’s hull insurers (if owners have insured) or of owners themselves. Moreover the concept of "safety" is necessarily not an absolute one. As the Court of Appeal said in The Saga Cob  1 Lloyd’s Rep. 548 at 551, column 2, in the context of political risk:
"In the latter case [the safe port warranty] one is considering whether the port should be regarded as unsafe by owners, charterers, or masters of vessels. It is accepted that this does not mean that it is unsafe, unless shown to be absolutely safe. It will not in circumstances such as the present be regarded as unsafe unless the "political" risk is sufficient for a reasonable shipowner or master to decline to send or sail his vessel there."
53. A similarly realistic approach has in our view to be adopted to the determination of the essentially factual question whether the event giving rise to the particular casualty is to be characterised as an "abnormal occurrence" or as resulting from some "normal" characteristic of the particular port at the particular time of year. We emphasise the word "normal" in the term "normal characteristic". It was used by Lord Diplock when he observed in The Evia (No. 2)  1 AC 736 at 749 that:
" … it is not surprising that disputes should arise as to whether damage sustained by a particular vessel in a particular port on a particular occasion was caused by an "abnormal occurrence" rather than resulting from some normal characteristic of the particular port at the particular time of year."
56. … instead of asking the unitary question directed at establishing the correct characterisation of the critical combination (abnormal occurrence or normal characteristic of the port), the judge merely addressed the respective constituent elements of the combination (swell from long waves making it dangerous for a vessel to remain at the Raw Materials Quay and gale force winds from the northerly/northeasterly quadrant making navigation of the Fairway dangerous or impossible for Capesize vessels) separately. He looked at each component and decided that, viewed on its own, neither could be said to be rare and both were attributes or characteristics of the port. That was the wrong approach; what mattered was not the nature of the individual component dangers that gave rise to the events on 24th October, but the nature of the event (i.e. the critical combination) which gave rise to the vessel (on the judge’s findings) effectively being trapped in port.
62. The second reason given by the judge ("Even if the concurrent occurrence of those events is a rare event in the history of the port such an event flows from characteristics or features of the port") is, in our view, equally flawed. As we have already stated in paragraphs 55 and 56 above, what the judge had to decide was whether "the concurrent occurrence of those events" (i.e. the critical combination) was itself a normal characteristic of the port or an abnormal occurrence. That was the relevant event which the judge had to characterise. It simply did not follow, logically or otherwise, from the fact that that event arose from (or, as the judge said, "flow[ed] from") the combination of two individual dangers, which he had held were normal characteristics or attributes of the port, that the "concurrent occurrence of those events" was also a normal characteristic or attribute of the port.