The frame rebuild could take on several approaches, each with pro's and con's. I've scoured the Investigator web forum to see other I 563 trailers. There are a wide range of designs from different manufacturer's. Some have mechanical brake systems like mine, others have hydraulic brake systems. The original wheels were just 13" with a straight axle (to get keel base lower). Allot, like Teria's, have larger wheel rims with an offset axle.
Some trailers have what appears to be 4" or 6" high main long beams in Channel or box section.
Some trailers have 3"x 1.5" channels for cross beams. Others have only 2" high (box?) cross beams.
Also looking at other TS and large powerboat trailers too.
Choice of materials.
a) Use black steel box beams with final hot-dip galvanizing
b) Use C-channel beams with hot-dip OR pre-galvanized with cold gal paint on welds.
The only problem with box beams is that once the trailer frame is hot-dipped, then extra modifications can't be welded on later. The weld heat would burn off the galvanizing inside and create a future hidden rust spot. So things like side bunks/rollers must be U-bolted on, this is OK as then they are fully adjustable, can be moved or re-moved. Allot of Investigator 563 trailers have this system.
The open C channel beams would allow later weld customization. All existing and future fittings can be welded straight on. The other advantage of this would be in later trailer life it could be corrosion maintained so might last longer.
Choice of specifications
1) "Like for like" - replace with 3x2" beams. Add a 1/2" reinforcing steel rod rail about 2" above the frame.
2) Increase the vertical width to 4 or 5 inches for side frames.
A few variables to think about. A main consideration is to keep the trailer weight similar to the original. Visited the local steel supplier and picked up a steel stock specifications booklet to study, it has mass/meter for every steel section. The C - channel section has greater wall/ flange thicknesses than same sized box beams for the same outer dimensions..
Draw bar length
Increasing the draw bar length would be good. Teria's trailer's draw bar was only 1.1m long (3'7"), way too short for my tow-car setup. 1.8m long (6') or more seems far better. The length could vary depending on the location of the pivot hinge and length in front of A frame. A long draw bar would allow for back wheels of the car to remain dry and get the hull in deeper at the launching ramp. Turning circle may alter,?? If the winch post is further away from striking the ute's tray with a long draw bar it may actually help with tighter turns.
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