In case you rent a yacht as Bareboat, meaning that you or a friend of yours, will be the skipper of the yacht, it would be a wise idea to have an extra insurance. This extra insurance would cover the amount of the guarantee that is given for the yacht rental.
Many companies provide such an insurance, but if you do not know any, below you can find a useful link https://www.pantaenius.com/de-en/insurance/charter/?adid=2316