Your opening statement is true. Keeping the tramp tensioned will result in a stiffer boat that will improve through the water performance.

Tensioning is pretty straight forward. First loosen all the tramp lines. Get a tape measure and with a friend make sure the boat is square. Measure from the port bow to the starboard stern. Do the same from the starboard bow to the port stern. If the measurements are diferent move one of the hulls forwards or backwards until both measurements are the same.

Now it's time to tension the tramp. There are tools available to do the job but vice grips work fine. Start at the bitter end of the line and pull it as tight as possible through the closest grommet. Work your way through all the grommets until you get to the other end of the line. Tie some half hitches and you're all set.

Recommendations: Use non-stretch line so you don't have to repeat every time you take the boat out. In the past some used large diameter bungee. It works but seems to wear faster than good line.

Think about double grommeting. This will give you an additional purchase to stiffen the boat.

Take your time doing the job and you'll have a stiffer boat.