I'm putting together a trailer for my buddies airboat, and I have a question or two about tandem axles.

I need to know how far apart to set the spring hangers. I've done a couple of single axels before, but the tandem has me stumped. Eye-to-eye on the springs is 25 3/16", and eye-to-eye on the tandem coupler is 5 3/4".

Also is it "better" to have the springs set over the axle, or under? I guess the better question would be what are pro's and con's of either?

Thanks in advance for any help on this one. I know there are a couple of trailer guys on here, and some of the previous posts have helped a ton already on this project.