crack goes the trailer

[ifishcq1]

The other day I was taking the boat down to the harbour when I heard a big cracking noise
I pulled over and saw that the boat was holding the trailer together
back home for some roof screws and a couple of pieces of c channel dodgy repair then home again
drop the boat on the ground and head up to Fubs place with the scrap metal hanging off the back of the disco
this trailer was oil filled from day one drained yearly and filled again, every time there was a layer of salt water under the oil
despite "o"rings on filler hole seals
7 years of upto 2m under at the deep end exerting 4 times the water pressure of the average trailer takes it's toll
new trailer needed
points to consider
1/ new trailer $12,000+ for 11m = home build instead
2/ box section is crap so no box except the winch post
3/ reduce trailer flex putting pressure on hull
the verdict is c section in heavy size
the shopping list is 24m 125mm x 65mm x 10mm C, 24m 100mm x 50mm x 8mm C, 6m 75mm x 100mm x 8mm angle
new hubs, bearings, galv 6 leaf springs, two tandem kits
reuse guards, brakes, lights and hitch
the black steel will be sprayed with phosphoric acid, rinsed then two coats of bitumen paint on all surfaces except winch post and galv springs
should save around $8,000
http://i1248.photobucket.com/albums/hh497/cqfisher/2.jpg (http://s1248.photobucket.com/user/cqfisher/media/2.jpg.html)http://i1248.photobucket.com/albums/hh497/cqfisher/3.jpg (http://s1248.photobucket.com/user/cqfisher/media/3.jpg.html)
updates as constructed
cheers

[kaypee]

Ahh this thread :)
sheeesh mate, you'll need an Chevy to tow her!! Hope she comes together for the trip! Although u'd probly be better in the KC anyhow ;)

[ifishcq1]

Yeah Mick the draw out of the hat for deckies might go to those with the biggest truck
luckily I only have to sit on 80k/h from home to the harbour so the disco will do the job
we checked out a backhoe trailer today and I recon we could get a bobcat on too
but I could settle for the KC at a pinch ;D

[tunaticer]

Mate, I hate to be the one to give you the news, but that trailer is going to flex like a bastard.
For it's length the 125PFC is woefully inadequate to control flex.....the cross members are fine.
The actual support either side of your axle sets will be minimal and with road and towing forces you might find your keel will only be supported by the few members directly above the axle sets. Either side of that will flop up and down.
I would be looking for 180UB minimum.....probably opting for 200UB25 for the main girders.
100x50x4mm RHS is about 30% stronger than the 125PFC you have selected as a comparison.

[gr hilly]

Ill be looking for a disco at 60 ft in the air.

[gruntahunta]

Yep...I have always thought that if C channel was better for trailers than RHS, they would make them out of it.

[Noelm]

Yep...I have always thought that if C channel was better for trailers than RHS, they would make them out of it.

They use RHS because it is a lot easier to work with, looks better and is a lot easier to just buy in almost any size you like, but it is not all that flash for a boat trailer, box trailers and caravans for sure. if I was building another trailer now, especially for a cat because they are so simple, I would use I beam I reckon.

[stang69]

Mackay trailers in Melbourne make C-Channel steel trailers. I have seen a few other makes too, but not sure what brands.
Definitely makes more sense than RHS.

[Noelm]

back in the "old days" almost every trailer was C section, the old Brookers and Jawar and so on, and most of them are still alive today after near on 30 years or more use! mind you some of the badly neglected ones have gone to god, but those that were reasonably well looked after are still good. can't say that I have ever seen a 30+ year old RHS trailer.

[stang69]

I wonder how long all these chinese trailers will last. Not many Australian boat trailers built here anymore. They seem to be mostly imported, or just assembled here from imported chinese parts.

[Noelm]

I know the CHEAP Chinese trailers are "cheap" and I don't expect them to have a long life, some of the others made to a standard could be OK though, I think Dunbier are still made here?

[stevej]

for the aussie built ones are they using australian steel here ? or just chinese steel welded up here ?

the diff in price between aussie and chinese steel is significant

[snapperbasher]

Not really by the time you land it here..... cheaper yes butnot significant....

Fabricated steelwork is a whole different story..... Chineselabour is negligible against ours. Fabricated/galvanised structural steelworkcan be landed in Australia for approx $1800-$2000 /ton. Australian fabricated/galvanisedstructural steel cost exfactory starts from about $3500/ton.

Steel = $1350/ton
Labour = $1650/ton
Galvanising = $550/ton

[SunnyCoastMark]

if you weld a truss frame on top of the side channels from something like 25 NB Medium pipe. That will stiffen the trailer right up and take out almost all of the flex. Use 16mm round bar as your v section - just need an oxy to bend it in to that continuous W shape. Also allows you to tie down anywhere along the length of your trailer.

Mark

[Noelm]

Instead of a thousand "W" bends, I have seen them just have a long length of thick round bar, welded on the front, going up in the centre to a piece of (about) 75mm flat bar about 75mm long, then down to the back of the frame, seemed to work OK, kind of like one big "truss"

[Schulzy]

Continuous round bar spaced would be the go otherwise it would probably go along the road like a snake. Looks good so far!

[ifishcq1]

Thanks Guys for the very welcome input
before going too far with more construction I ran the car up onto the old trailer and it flexed about 300mm from the break back while the new frame only moved 9/10ths of bugger all over the whole length
when we add the spring cradle 100mm x75mm angle 3m each side, the draw bar carries another 3m under the main frame and is 1.5m long forward
that only left 2m at the back and 1.5m inbetween unbraced
we are aware of road shimmy and by adding cross braces (like a shed) that should stop that
We will do a road test before adding anything else
having put together longboat trailers before I pretty well know where they need support, but a trial will sort any issues
cheers

[wags on the water]

All over it like flies on sh!t Scotty - shame about the old trailer mate. Could have been worse - trailer and boat damaged....

[ifishcq1]

here guys just show how little room there is for shimmy or twist

http://i1248.photobucket.com/albums/hh497/cqfisher/004a.jpg (http://s1248.photobucket.com/user/cqfisher/media/004a.jpg.html)http://i1248.photobucket.com/albums/hh497/cqfisher/003a.jpg (http://s1248.photobucket.com/user/cqfisher/media/003a.jpg.html)
http://i1248.photobucket.com/albums/hh497/cqfisher/005a.jpg (http://s1248.photobucket.com/user/cqfisher/media/005a.jpg.html)
http://i1248.photobucket.com/albums/hh497/cqfisher/006a.jpg (http://s1248.photobucket.com/user/cqfisher/media/006a.jpg.html)
http://i1248.photobucket.com/albums/hh497/cqfisher/007a.jpg (http://s1248.photobucket.com/user/cqfisher/media/007a.jpg.html)

Cheers

[swallin]

Just wanting to clarify a few things in this post.
First up I am not an engineer but I do play with steel and can read specifications.

The section modulus (for simplicity Z) of a beam can be used by engineers to estimate the "flex" of a loaded structural member.

Someone mentioned that this build would flex too much going on to say that 100x50x4 RHS is about 30% stiffer than 125PFC.

From Bluescope specifications:

125PFC 11.9kg/m Zx = 63.5 Zy = 30.2
100x50x4 8.6kg/m Zx = 34.1 Zy = 17.9

So Zx is in the up and down direction of a trailer (think road flex) Zy is across the member (much less of an issue in a trailer where cross members give lateral rigidity)

So, in the up and down direction of controlling rigity 125PFC will flex half as much or is twice as stiff as a 100x50x4 at only 40% increase in mass.
125PFC is a much stronger section than 100x50x4 can ever even hope to dream of being.

Anyways I like the layout of the planned trailer but would have preferentially ran the PFC with the web outwards such that the spring plates have a better supported surface. This would have required notching each cross member but this in itself would be a stronger join than welding web to web. But no matter that thing will still be a beast of a load carrier. One thing to watch with Bituminous paint is that some species of native bees up north just love the stuff and will eat it off the chassis!

Steve

[ifishcq1]

One thing to watch with Bituminous paint is that some species of native bees up north just love the stuff and will eat it off the chassis!

Steve

Funny that they also love the glue on duct tape and swarm over it until there is no glue left
maybe I just keep a roll of duct tape handy until the bitumen goes hard

cheers

[Noelm]

Why not just get it hot dipped? I know there is all sorts of paints and preparations for new steel, but hot dipped, and then coated with "something" before it ever gets wet will last a very long time.

[ifishcq1]

Hi Noel I took your advise after APG came back to me with a fantastic price so galvanising it was
now fit off get it home and get the boat on it
http://i1248.photobucket.com/albums/hh497/cqfisher/backendtrailer1.jpg (http://s1248.photobucket.com/user/cqfisher/media/backendtrailer1.jpg.html)
http://i1248.photobucket.com/albums/hh497/cqfisher/trailerfront.jpg (http://s1248.photobucket.com/user/cqfisher/media/trailerfront.jpg.html)
http://i1248.photobucket.com/albums/hh497/cqfisher/trailerside.jpg (http://s1248.photobucket.com/user/cqfisher/media/trailerside.jpg.html)
http://i1248.photobucket.com/albums/hh497/cqfisher/trailerlength.jpg (http://s1248.photobucket.com/user/cqfisher/media/trailerlength.jpg.html)

[Noelm]

Yeah, seeing as it was all nice and new, getting it galvanized would have been reasonably priced, now paint it with "something" whether that be fish oil or some proprietary product, and the trailer will last you for decades, I recently saw an old trailer that I had back in around 1985 (a Jawar) under my old cat, and it is still good, I covered it in something called Emperite?? And then fish oil sprayed on it every 18 months or so, looks dirty, but still not rusted.

[TheRealAndy]

I have had a couple of c section trailers now, and none have ever been gal. I just drown them in the cheapest crappiest enamel paint on a regular basis!

I must admit, the gal looks the part though!

[CATchin'Em]

Wouldn't that trailer require all wheel disc brakes and breakaway etc. thought she would be over 2t loaded. Also the reason box is used is to please engineers the twist in c channel is terrible especially in trailers when we have roads like we do. I built my new trailer out of box and my old trailer was box it was over 20years and wasn't even hot dipped and never broke and I still use it as a car trailer(not in bad nick actually) Make sure you use a duralac or tef gel whereever you bolt anything together.

[ifishcq1]

Hi Catchin'em those spacers where the ubolts go has stiffened the little bit of twist it had before we put them in we took the boat from Cawarral ro my place over the dirt road and it moved bugger all and then we stuck all the plates in and there is nearly no movement
so compared to my box section trailer this is much better, this is better than I hoped for
I double sprayed all the ubolts and will keep all low section parts coated in fergusen's

[ozscott]

You could do a lot worse than painting Xtroll Rust Conqueror UV on it and then eazy gal over the top.

Cheers