Thread: Trailer Tech...???

I've seen a boat trailer that had a slide on car tray. Just had a frame for the car tray and angle underneath that sat over the outside edge of the outer frame of the boat trailer.

Ben,
How big a boat are you talking about.
If it is for a small (<5m) relatively shallow V (like a tinny) then I generally make off-road boat trailers without curved or Veed cross rails. (gives guard clearance for offroad tyres and shock absorbers.)

In light of this you would build it as a flat chassis (100PFC) with a central row of rollers for the keel. Then have adjustable bunks left and right for the hull. These bunks would then be removed and say a framed up Al box with centre keel winched up the centre and bolted down.

Rego would depend on how dodgy you are. Pick which style you will most offten have the trailer setup and register accordingly. As long as you stay under the GCM for the trailer the fact the little sticker says 'boat' not 'box' shouldnt raise too much ire.

S

alternately, what about building a suitably sized box trailer with removable front and rear boards and a drop in cradle/frame?

Yes, depends on the size of boat and trailer.

Friend of mine had (many years ago, may still have it) exactly this - basically it was a box trailer with front and rear boards that dropped into slots, and for boat carrying they were replaced by ones with a top profile to suit the boat and padded. Only a dinghy though. it sat very low, as the trailer was based on the complete rear subframe of a Mini.

John

In Queensland at least there is no inspection process for trailers (or wasn't last time I registered one). If it is less than 750kg or single axle you don't even need a roadworthy, in many cases transport doesn't even look at the trailer, so you can register a rusted out hulk of a boat trailer and then fix it at your leisure. And if it is home made that isn't a worry because they can issue you with a VIN plate and new VIN number for it. Geez we are liberal here in Qld!

Not sure about other states though. We used to have a boat trailer that was modified to carry a ride on lawnmower. The central rollers all undid and slid out, the side skids for the hull stayed and were used to attach tie downs. Then we fixed a pair of wooden planks at the correct spacing for the wheels and bingo! We could use it to carry larger flat stuff too. You can get folding trailers that are designed to stand up in a small side courtyard, so not much difference between these and making a combined box/boat trailer. Our rego labels don't specify which type of trailer it is, just that it is a trailer.

Originally Posted by roverrescue

Ben,
How big a boat are you talking about.

~5m plate boat.

Trailer rego would not be a problem; it is essentially about the chassis, there are off the shelf convertible trailers available. In QLD they would want details of the largest possible configuration for the rego details. Once again in QLD; if the ATM is less than 750kg it is not even inspected. Over 750kg it is – new (never registered) is only QLD Transport no roadworthy required, 2nd hand requires a roadworthy. 5m platey is definitely over 750

I think there are some good suggestions above for a 5m craft; you would end up with a very long and wide box trailer, but what Sprint has suggested would be the go, it may create a challenge to keep the rust out, as the floor and subframe would see the salt regularly, but manageable (or build it all in ally). The boat would be higher than normal, but it could tilt for launching (be a bigger problem for dropping boat on the grass). And the axle group would still need to be adjustable. Think you would only need to drop in keel rollers (tube adjusters built into floor) and some type of cradle to accommodate side wobble rollers or slides.

roverrescue’s model would result in much heavier trailer especially in it’s box configuration, because it would need a subframe + the base chassis. Usually a trailer with any sides (box or even car carry) requires less chassis or subframe than a boat trailer because the sides of the box welded to the subframe create a lot of strength (in the way of a truss). It would also create a high floor for the box trailer, if that’s a concern that could be rectified by building in overly veed cross rails to lower the keel roller line, but then guards fowling on the chine would have to be checked… But it would be very heavy.

Be aware of water traps duing construction.

Awesome topic – love thinking outside the square for a build, lot of people won’t accept anything that’s not mass advertised or a copy of something that is – get ready for the knockers!

Thanks for all the advice/replies!

A few basics:
I was thinking a single axle (probably a complete RRC/disco rear axle casing - suitably modified - rotated 90 deg and with the centre hole plated) running 235/85-16s. Suspension will be RR/LR front radius arms turned around the other way, and probably air springs.

This way the wheels, hubs, and even air springs can be kept identical to the tow vehicle (I will be carrying 2 vehicle spares on long trips...).

The load rating of the tyres would be ~3T, and the axle would cope. However - what do people think of this idea? Would it be OK on soft sand?

What braking setup will I need?

A mate who has done LOTS of sailing and boating (professionally and recreationally) has suggested that the best setup is all slides and no rollers. What do others think?

As I already have a ute, I think the trailer will only occasionally be used as a box trailer. So I am tempted to use it primarily as a boat trailer, and maybe include permanent weldmesh floor, fill in the space under the side skids with weldmesh, so then a conversion to a box trailer would simply mean removing the boat and fitting a front and rear (mesh) tailgate?

The above option seems the best way I can think to keep the weight down...? In the unlikely event I want to carry dirt/sand/gravel in the trailer I can always fit some ply over the weldmesh...

The whole thing will be galvanised (including the axle), so the only rust problems I should have will be with the shocks...