In regard to YupSail, I have no experience with that particular firm, but a couple of things I'd be very very wary about.
1. While most other parts of their website is written in English, their terms and conditions are not. Instead they are written in Italian which if you don't understand, it puts you at an immediate disadvantage because you don't know what you are letting yourself in for. In a worst scenario, this is your boat, your investment, and your pride and joy. Responsible charterers will look after your boat, others may do so, and an irresponsibly large proportion of them won't give a dam about your boat.
2. What you need to know is how the charter firm will look after your investment, and how exactly you will be reimbursed for any damage done.
3. You need to know who will be responsible for ensuring that periodic surveys are carried out on time, who will pay for those surveys, how you will be notified when a survey becomes due, when and by who the survey will be carried out, and a cast iron guarantee that your boat will not go out if any survey is either not carried out or is not passed satisfactorily.
4. You need to know that on any charter agreement, that your name is included on that agreement as the person who owns the boat and with whom the charterers have a direct responsibility in regard to payment of any outstanding fees, and for any damage incurred which occurs as a result of any action taken by the charterer or crew which is not in strict accordance with the charter agreement, or is as a result of their negligence or through non compliance with any internationally recognised procedure or regulation such as, for example "The International Regulations for the Prevention of Collisions at Sea," or from failure to comply with any river, or harbour authority regulation, laws or bye laws, and that they will take full financial responsibility for any misdemeanour which may result in your vessel being impounded by any competent authority legally allowed to do so.
I have had experience of chartering out my boat through a firm located within the United Kingdom, where that firm failed to ensure that charterers took care of my investment, failed to maintain the surveys up to date, failed to advise me that they had ignored two separate notifications that a survey was due, failed to pay me the monies due from several previous charters, did not include my name as an interested party within the charter agreement such that when a collision occurred I could not take legal action against the skipper of the boat, the charter firm failed to go after the skipper of the boat for reparations, and did go bankrupt making it uneconomic to pursue the charter firm. I did however employ a debt collection agency who were able to collect the outstanding monies from the various charters up to and including that where the collision occurred, and no, the insurer did not cover the cost of repairs, because the survey referred to above had not been done, thereby giving them a get out.
My advice to you is that if you really desperately want to charter your boat out, only do it through a large and reputable charter firm, get everything in writing in regard to responsibilities, and get out at the moment you think the charter firm is not levelling with you. Better still, don't do it at all, and definitely not if you don't live near enough to where your boat will be based to enable you to check it out after every return from charter.
Sorry if that all sounds very negative, but there are sharks out there that will take you for every penny they can, and then leave you to count the cost. Undoubtedly there are some reputable firms, but their services have to be paid for, and it's not cheap. In addition there are skippers out there who blatantly lie about their sailing qualifications, as did the skipper (an Actuary for a well known accounting firm in Edinburgh) who caused my boat to collide with another, and who claimed to have a yacht masters equivalent certificate gained from a week's day sailing holiday at a large sea school. Naturally he blamed the boat for the collision with just so much bowllocks about it not turning fast enough, and his mate on the other boat made no attempt at all to avoid the collision. The parties on both boats were a large group of friends having a stag party, alcohol was involved, but no one was checked for it, and by the time I was informed of the collision (some eighteen hours later, plus another seven hours to get there), the boats had been cleaned leaving no trace of the alcohol consumed and both skippers and their crews had packed up and gone home. Statements were only taken from the two skippers with no mention of the hooliganism involved that day. That only became apparent when talking to other people who had seen the event, but who did not volunteer their information in time for it to make a difference.