There are a few examples of this here already. Just figured I'd offer my interpretation of a trailer/dolly combo. Maybe this will help someone, some day.
I'll start w/ pics of the trailer as I purchased it w/ the boat. I had already removed the rear bunk that was bolted to the back of the trailer when I thought to take pics.
Here's a few pics of the initial concept testing and fitting. I didn't have the tools to cut down a 4x4 (at least not w/ clean edges) for the center of the front channel. Luckily, a nice Lowe's Hardware lumber employee came up w/ the great idea of using a pallet strap block. It measured 40" L x 2.9" W x 2.5" H, close enough for gov't work! Plus it was free! It was rough but, a little work w/ the belt sander cleaned it up.
I found some cardboard w/ a factory edge and traced the wheel arches. Then used a roofing square to make sure the template was flush w/ the 2x4. I traced a 1" fender washer to shape the front end of the bunk so it's less likely to break off.
The bolt-on, retractable rachet straps were a nice find. much better than the old two-strap system for this. Very easy to use too. Press the red button, pull strap to desired length, hook, press the red button to retract slack, then secure w/ the rachet. (Erickson 34422 Pro Series 1" x 6' Bolt-On Retractable Ratcheting Tie-Down Strap, (Pack of 2)
Here's the final product. Had to move the trailer bow support rearward to meet the bow support of the dolly. Didn't seem to adversely affect tongue weight. I used a Trailer Axle Plate kit from eBay to secure the front channel. The kit contained: (4) 2 1/16" wide X 5 1/4" long X 1/2" diameter hot dipped galvanized u-bolts (2) 5 hole heavy duty plates hot dipped galvanized
(8) 1/2" lock washers hot dipped galvanized
(8) 1/2" nuts hot dipped galvanized
Total w/ shipping was $12.
Word of advice: cut the recesses in the base of the front channel for the u-bolts, before you screw everything together (or just un-do it). It'll make your life easier...
My remaining challenges:
- Find a roller that will better guide the center beam of the dolly. The first time I tested it, the beam of the dolly rolled off onto the trailer and bent as the weight of the boat came down on it.
- Re-wire the lights
Thanks to all those who previously posted info on this project.