Thanks for the comments Terry.
"Inspirational", would not be the word I would have chosen ... "painful" would be more appropriate after all the little snags and hassles and unanticipated cost I encountered along the way.
However, I am quite satisfied with the end result, and tow with a lot more confidence now that everything is working as intended. The one lasting downside is the added trailer height, which means I have to get the back wheels of my Land Cruiser tow vehicle wet at the ramps I use- usually to a depth of about 3-4 inches of water. Its not a major problem, but does mean I also have to wade into the water when when launching and retrieving and get more wet than was necessary before the upgrade.
Below is a long an rambling account of some of the pitfalls I encountered. It might make you reconsider an upgrade in favour of a completely new trailer from a reputable marine trailer manufacturer!
Capacity Plate.
The 5000 lbs should indicate the aggregate gross vehicle mass of the fully loaded trailer including the boat and all the gear you have on board. There should also be a tare weight that shows the mass of the trailer itself.
Galvanising
Yes the trailer has to be dismantled to be galvanised. This is not a big deal if a major upgrade is going to happen anyway. The painted trailer had to be sandblasted to remove all of the old paint and any existing rust and also needed some additional holes drilled in the square and tubular-section frame components. I think it then goes through an acid bath to get residual rust off before the galvanising takes place. I originally planned to get the leaf springs and axle galvanised, but it didn't happen and I have not pursued it. Similarly the rims have not been galvanised because the size change was a last minute thing. Hopefully, "one day..."
Options: I considered following the path of others on this forum and installing a dual axle system. The advantages would have been smaller wheel diameter, lower trailer and therefore easier launching. The disadvantages would have been loss of manoeuvrability (my boat yard requires me to back the trailer between other craft with only a couple of feet clearance on either side), difficulty with getting braking right (dual axles have some braking peculiarities that can be difficult to get right) and, from recollection, a higher overall trailer mass in relation to the payload I can carry. I think cost could have worked out marginally higher as well, but I would have be able to reuse some of the parts like axles and bearing that became obsolete in the single axle version. I'm happy with the route I chose.
Some of the lessons learned during my upgrade process:
1. If you can find one, use a trailer guy who has experience with marine trailers. I did not have a lot of choice in my area. The while one I chose had plenty of experience in building trailers of the tonnage I required through building horse floats and he had also done a bit of marine work, but not as much as I would have liked. Some problems would have been avoided had he/we thought them through more thoroughly.
2. Likewise with any electrical work. Find someone who has experience with both marine work and the types of brakes you plan to use. The guys who installed the electrics in my tow vehicle were chosen by my trailer guy and had (I found out later) no significant experience with trailer power braking systems or the marine trailer environment. They were also sloppy workmen and neither the brakes nor the extra power outlet I got them to install in the rear of the tow vehicle worked properly.
3. Find out everything you can about the engineering -registration requirements for your jurisdiction AND AVAILABILITY of necessary parts. Being quite naive, I had a lot to learn and found it difficult to get hold of useful information about the requirements in my State. My upgrade crossed a number of "mass thresholds" that forced me to upgrade some items I had not anticipated before the local authorities would register/certify the trailer. I also had problems procuring some items and that messed my plans up at the last minute.
The most significant items in the upgrade were:
* the frame itself (the original 26M trailer frame was in good condition and was okay. It is all that is left of the original trailer);
* the bearings and hubs (had to be replaced with ones with a higher load-rating);
* axle - (had to be replaced to match the required load rating - the square section axle I have is solid steel (not hollow) and is rated for 3 metric tonnes)
* springs - (had to be upgraded to meet engineering requirements for the higher load rating. These also added some height to the trailer)
* rims and tires (had to be replaced. I had originally planned to use the 16 inch rims fitted to the Australian version of the trailer, but at the last minute the trailer guy found out that he could not get tires with an adequate rating unless I went to 17" light truck tires. Even then he was limited by availability in this Australian backwater, so the best I could get in that diameter were only rated for 1.4 metric tonnes each. As a result my trailer was only registered for 2.8 metric tonnes instead of the 3 tonnes I had originally planned.
* don't forget that tires age and that age has nothing to do with the tread on the tire. My trailer guy went for second hand tires that were cheap but were already 7 years old and well past their safe use-by date. I have since replaced them.)
* fenders or mud guards - (fairly obviously these had to be modified to allow for the large diameter wheels and tyres. The new fenders were not part of the original plan, although the design is a lot better than the factory originals.)
* safety chains - ( had to be upgraded to match the requirements of the higher mass)
* tow-hitch, tow-ball and coupling -(the new ones on both the car and trailer are 50 mm (around 2") but are rated for 3.5 metric tonnes.
* brakes - (the original disk brakes were inadequate for the mass requirements and had to be replaced. I knew this would be the case and originally planned to use stainless disks but couldn't get them at the time. The steel disks have proven to be okay so far and rust doesn't really seem a problem.)
* brake actuator - (the most expensive item! The original surge brakes were deemed inadequate for the trailer's target gross vehicle mass of 3 tonnes. To meet registration requirements I had to install an electric-hydraulic system (Hydrastar), a system that has and on board electric hydraulic pump powered by its own trailer-mounted battery. It has an inertia sensor mounted in the tow vehicle to control braking aggressiveness and also has a trailer-mounted breakaway switch that activates the trailer brakes fully in the event that the trailer breaks away from the tow vehicle. I had a lot of trouble getting the electrics for the braking system on my tow vehicle working properly until I took the car to someone who knew what he was doing.)
*trailer lights - (I originally tried to use the near-new and so called "submersible" incandescent lights. Bad mistake. LED's are definitely the way to go.)
*trailer wiring - (Don't trust shrink wrap insulation for trailer wiring junctions! It is not a great insulator and only waterproofs a join if it is perfectly applied. LED's are quite sensitive to any current leakage and salt water is a good enough conductor to power the LEDs. I overcame the insulation/water seepage problem with liberal application of liquid electrical tape, but I wish I had applied it before the trailer went anywhere near the salt water. With hindsight I would probably have used BOTH liquid electrical tape to ensure a good seal over all junctions, and shrink-wrap insulation on top to add strength.
* final trailer weight - unladen my trailer went from around 300 kg to 520 kg. My new net payload for the boat plus gear is therefore just under 2300 kg. I think that's enough
.
And last but not least, the tow vehicle has to be capable of (legally) towing the extra gross trailer mass. The vehicle I had originally would tow everything quite well but was only rated for 2000kg so there were major legal and insurance implications in the event of an accident.
