Thank you. Any claim would be made under the Consumer Rights Act 2015 as that deals with the provision of services and also you would be looking at general damages under common law for breach of contract, which can allow you to claim for loss of enjoyment as well.
The direct losses you have suffered as a result would be the remainder of the holiday, assuming it was all paid for. As you still continued with the holiday for several days, your other potential claim would be for loss of enjoyment during those days. This would reflect the time spent on the boat for which you paid, but which was ruined by some breach of contract or misrepresentation by the company. There is no precise science as to how such compensation is awarded and each case will depend on its own circumstances. Generally a quarter to a third of the value of the holiday would be considered reasonable. A lot would depend on what was actually wrong, whether you should have known about it (taking into account the advertisements, brochures what you were told at the outset, etc) and how a reasonable person may have seen these issues and their seriousness.
Whilst there is nothing stopping you from rejecting the latest offer and continuing to negotiate, if you do so and take the matter further, you may have to go to court to seek further compensation. The risks increase because you will have to pay for this (no legal assistance is required unless you decide to use it) and there is no guarantee you would get what you were hoping for. You may nevertheless take the matter as far as you wish and continue negotiating with them in the meantime.
This is your basic legal position. I have more detailed advice for you in terms of the steps you need to follow to pursue the matter further, which I wish to discuss so please take a second to leave a positive rating for the service so far (by selecting 3, 4 or 5 stars) and I can continue with that and answer any further questions you may have. Don’t worry, there is no extra cost and leaving a rating will not close the question and we can continue this discussion. Thank you