FtLbs
It's just simple math. Take the amount of weight you are placing behind the axel and multiply it by the number of feet behind the axel. That's how many FtLbs of lift you have created. Now measure the distance from the hitch to the center of the axel, take the Ft/Lbs from the first calculation and devide it by that number and you will have how much you have decreased your tongue weight. Note, you will need at least 10% of the weight of the tow on the tongue or you can have a bad problem with sway at highway speeds. 10% works great on campers and box trailers, but depending on how the tow vehicle breaks the wind, wind pushing up on the bow of the boat can decrease your tongue weight at highway speeds. This will cause sway. Make sure your trailer is level or slightly down by the bow to help reduce this. Don't worry about having too much tongue weight, short of exceeding the tows max safe tongue weight. A trailer with 60% tongue weight will tow much easier than a trailer with 10% tongue weight, but you wouldn't want to buy the truck that has a safe tongue weight ability at over 2000Lbs. Check your owners manuel and see what it says is your max safe tongue weight and get close to that and your trailer will tow better. Check on the max gross trailer weight too, and max gcw too.