From it's latest 9.4 release, Booking Manager allows you setup maximum discount on individual boats regardless of the Maximum total discount set in the system.
1. Check Maximum total discount limit
In the Preferences > Reservation Settings > Invoice, there should be a maximum total discount option set. Please check if this option matches your company conditions. Usually companies set this to a maximum of 15 to 20 percent.
2. Set the maximum discount on an individual boat
If you want to set the maximum allowed discount on a individual boat go to Work > Yachts and select a boat (1.). Then find the Maximum discount field and enter the percentage of the maximum discount (2.). Press Apply (3.) when done.
Repeat this for any boat that needs to have maximum discount individually set.
3. Removing the individual discount
If the specific discount is no longer required, select the boat again (1.), click on the delete icon next to the amount (2.). and press Apply (3.).
Again, repeat this on any boat that no longer needs a specific maximum discount.