Determining Correct Replacement Slipper Spring For Boat Trailer with 3,700lb Axle

Updated 06/13/2023 | Published 06/12/2023

Question:

Looking for the appropriate slipper spring weight for boat trailer. A generous estimation of the boat, motor, battery, gear, etc weighs 1900lbs. The trailer weighs just under 1000lbs. The 2inch square axle is rated at 3700lbs. I see two options for 1.75x30inch multi-leaf slipper springs at 2900lbs and 3700lbs. Which one would be the correct option? I dont want to under or over-suspend the boat. Interestingly, the factory spring is a single leaf, which is similar to your significantly lower weight rated models.

asked by: John

Expert Reply:

Based on the weight information you provided, you'll want to go with a 3,700lb slipper spring, though you need to figure out the length of your current spring first.

It's never a great idea to have a spring that's right at the max, as you're asking for a short life of the spring due to it always being used at its max. Having a little bit of a buffer is a much better idea for ride and spring longevity.

The etrailer # e89SR is rated for 3,700lbs and measures 30" from the center of the spring eye to the end of the spring, and is likely what you'll need. You need to jack up one side of your trailer taking all of the load off of the leaf spring, and then measure it this same way.

expert reply by: Samuel C