Patience is a virtue!
It is important to ask the boat owner all your questions about the boat you wish to book. If the boat owner doesn't respond, you can always send them a booking request, however you take the risk of your booking request being accepted but the answers to your questions not suiting you.
In order to avoid this, don't hesitate to contact other boat owners on the platform who are maybe more reactive.
You wil be able to see this thanks to the "Super Owner" badge given to boat owners who have a good response rate, and who receive positive reviews from other renters.
If you wish to rent several boats for the same date, make sure to select the option "I want to rent several boats".