Shoreland’r has an excellent website with much information on boat trailers.
http://www.shorelander.com/pages/forum/f_trstep3.html
Here is an excerpt from the above page:
To determine proper tongue weight, total the package weight (boat with fuel/battery, motor with maximum horsepower, and trailer) and multiply it by 6% on single axles and 5% on tandem axle trailers. ShoreLand’r suggests that tongue weight may be acceptable in a 5-7% range.
I had to move my axel about 15” forward to get the recommended 6% tongue weight — it made a world of difference in ease of towing.
Dave Gulczinski