Some charter parties expressly provide for certain requirements related to documentation in general and to letters of protest in particular.
Very important role of Letters of Protest is that they usually form a part of documentation submitted by the shipowner in support of his demurrage claim. For this purpose their legal effect, in the meaning described above, is not of much importance so far as they comply with requirements stipulated by the charterers.
Per Mustill LJ in Transgrain Shipping B.V. v Global Transporte Oceanico S.A., (the Mexico 1),  1 Lloyd’s Rep. 507:
…the assembling of a time sheet is an important part of business in the port. For [the payment of demurrage] purpose certainty is essential.
Per Judg Mackie QC in High Seas Venture Ltd Partnership V Sinom (Hong Kong) Ltd  EWHC 673 (Comm), at para 13:
13. As I see it the SoF is not final and binding because it does not say so and because the words ‘on the basis of’ [in cl. 11 Demurrage and Dispatch Clause] do not point clearly enough to finality. Similarly it may be too dogmatic to describe the effect of the SoF as reversing the burden of proof. The word ‘mutually’ is perhaps an unhelpful choice by the draftsperson but I take it to mean, at the least, around the same time. But the evidential value of the SoF is unquestionably strong whether or not the requisite mutuality is achieved and almost regardless of its contractual status. We have a statement of facts prepared on the spot by the agent confirmed at the time by the Master and, albeit much later, by the Port Authority. Stepping back from the fact that this is a specialised area of law, that is powerful evidence in any civil case to set against potentially self serving recollection and reconstruction of unremarkable and detailed facts, albeit assisted by weather records and other contemporaneous documents two years later. In general this evidence is likely to discharge the Charterers’ burden of proof unless the Owners show it to be wrong, an exercise which requires more than speculation and needs convincing live evidence and/or persuasive contemporaneous documents. Further, although this factor plays no part in my decision, the court should lean towards seeing finality when documents like the SoF are available as the unsatisfactory exercise which I must now conduct confirms.