Re: suspension stiffness
Mine has the shackle and I cleaned and greased it. The boat only weighs about 2000#. I might try taking the bottom 2 leafs out and see what happens.
I gotta laugh at this. I had the most disappointment with one of the "fit everything" type trailers with holes punched in the side rails so that you could move the spring/axle assy fore or aft to suit the boat being carried. This is also the one that had no shackle on the rear; just had the bare spring bent horizontal the last 3-4 inches and it fit into a socket sort of thing to keep it in place.
Anyway during that period, I did a lot of tinkering trying to smooth out the ride and in one instance, I just installed a different set of multileaf springs with the rear shackle. The springs were still too much for the light boat so I did just what you said; I pulled out the lower leaves, like one at a time thinking I'd get to a point where the boat would ride comfortably.
Well, those lower short leaves have a purpose and when you remove them, the longer springs have no support in the middle. So, when you hit that humongous unsuspected chug hole the axle comes flying up and the spring bends (takes a permanent set) right where the center alignment bolt hole is and since spring steel is tempered, it can and will break.
So BTDT; I think removing leaves is not the right answer unless the spring was professionally designed like that.
My 2c,
Mark