http://www.sherline.com/lmbook.htm#refrn9
Single Axle: 10% minimum - 15% maximum
Tandem Axle: 9% - 15%
Travel Trailer: 11% - 12%
5th Wheel: 15% - 25%
http://www.diynetwork.com/diy/bo_maintenance_repair/art...3718_2277896,00.html
Trailer Tongue -- This is the next boat-trailer component that Greviskis talks about. It's the long piece (see photo, right) that goes all the way down the boat trailer, from the coupler on back.
The perfect weight distribution for the trailer tongue should be eight percent of the total boat and trailer weight combined.