Yes, you can negotiate the purchase price from MSRP. No, there is no 'discount'. Like an automobile, there is no standardized percentage of discount off of MSRP. Each boat, situation, dealer and buyer are different and there are too many variables to come with a standard 'one size fits all'.
If you're looking for a deep discount, look for a demo model or a new boat of an older model year left over. (e.g. a new 2016 or 2017 model). You will be limited in option packages and color schemes.